If your question isn't answered in any of these FAQs, ask it on alt.guitar.amps !
*They do pull straight out. Really stubborn ones might need a little *rocking in a circular motion (not much). *DO NOT twist or turn. * *Don't worry too much about breaking the glass... they are *much* more *sturdy than a light bulb. * + I'll add that you should put your hand over the top of the tube. + Otherwise, you are likely to break it if it hits the cabinet. + !Is this from too much force applied to the pointy thing on the top...? !I've had them roll off a bench onto a tile floor and survive. You're lucky when a tube survives a fall. They don't always survive. I suggest placing your hand over the top because if it is kind of "sticky" coming out, when it does release, you are likely to slam it into something and break it.-John King, Jim Anable, John Wood
NOTE! Tubes get really hot in a very short period of time!
Allow them to cool, or use an over mitt or other protective
device to remove hot tubes. Do not lay them on a cold surface,
a wet surface, a flammable or meltable surface, etc.
-Miles
This is one of the most frequently asked questions. And you'll probably want to ask it yourself, on the group. Just be sure you ask it right.
First off, we will recommend you play as many amps as you can. Go to music stores, friends' houses, wherever. Find out what you like. If, however, this won't work (you're overwhelmed, live way in the boonies, don't have transportation, etc), you can skip this step for now.
If you still want to post and ask for recommendations, please include the following information.
Then, go play all the recommended amps that sound interesting, if at all possible. If your only possible option is ordering an amp based on the recommendations, then that's what you'll have to do. Just remember that tone is subjective, and what works for someone else (even everyone else) may not work (at least best) for you. In the end, you're the one who has to like the sound!
-compiled from various posts on the subject
Don't we all!
Rich's answer:
``NO!!!!!!!!!!!!!!!''
Short answer:
In general, you should match impedances. If you must mismatch, mismatch in the right direction, but stay as close as possible. So what's the right direction?
With tube gear it's better to have the speaker impedance lower. Connecting a 4 ohm load to an 8 ohm amp may be OK, but connecting a 16 ohm load to an 8 ohm amp is probably not. Connecting a 16 ohm load to a 4 ohm or 2 ohm amp is begging to destroy the amp. Running too high of a load on tube gear can fry anything (and occasionally everything) in the outputs, including tubes, transformers, resistors and tube sockets.
With solid state gear it's better to run a higher impedance. Connecting an 8 ohm load to a 4 ohm amp should be fine. Running too low of a load with solid state will fry your output transistors, and possibly more.
For more information, and to see when you might be able to get away with impedance mismatching in the wrong direction, see LV's explanation ("Long Answer") below and the AGA Technical FAQ.
-Miles
Long Answer:
Actually, this thread pops up every month or so. It always winds up the same way, too... the guys who know their stuff tell everyone that it's not a good idea to run a tube amp at a higher load impedance than it's looking for, and a bunch of other dudes chime in with "Oh Yeah? I ran my (whatever) into a 16-ohm cabinet for years and it was rated for 8 ohms. What about that?"
Well, this is what about it: sometimes it'll be OK. Things are different from amp to amp; playing style and signal type factor into the equation, too. A player who plays loud, with lots of treble, through an amp with high plate voltage (old Marshall, Orange, Music Man, older Ampegs, etc.) is much more likely to wind up with arced sockets (or worse) than a dude who plays jazz, with bassy tone, through a Fender amp with 430V on the plates. The type of mismatch matters, too... running an 8-ohm amp into a 16-ohm cabinet is less likely to cause problems than running a 4-ohm amp into a 16-ohm box. Running a downward mismatch will eat your tubes up a bit faster, but if your amp has a good output tranny that's probably the only thing that will happen.
Older Fenders have an extension speaker jack that's wired in parallel with the main one; if you plug an extension cab into a Twin Reverb (for instance) the load will be lower than 4 ohms, no matter what the box is rated at. If the amp was going to be damaged by running a load that was lower than the rated impedance, it stands to reason that Fender would have wired the jacks in series. They didn't, though.
A downward mismatch is usually OK, or at least it's better than the upward variety. I see a few Super Reverbs every year that have been re-speakered by their owners; they go to a lot of trouble to find out how to do a series-parallel hookup for the speakers because they "know" that the amp should be running an 8-ohm load. All of a sudden, the amp starts sounding like crap and blowing fuses. A Super Reverb wants a 2-ohm load; running it at 8 ohms pretty well guarantees you'll be making a substantial contribution to the Lord Valve Home for Lord Valve. (My favorite charity.) Of course, there will be a few "experts" who are convinced that SS amps and tube amps respond to improper loading in the same way. They're wrong, no matter how loudly they may screech.
As far as solid state amps go, it's a lot more straightforward... if you go below the rated impedance, you're going to smoke something unless the amp has really good current limiting in the output stage. Running a higher-than-rated impedance is just fine... you get less power output, of course, but the amp will run cooler and last longer. You can run a SS amp into an open circuit 'til the cows come home, and it won't do jack to it. Run a tube amp into an open, and you'll probably arc a socket (or worse) with the first note you play. It's a really common failure; I do three or four a week, year in, year out.
-Lord Valve
StratMatt's non-technical explantion:
I wanted to know the facts on this so I asked Mike Soldano when I picked up my amp. After explaining it to me in detail (as he does with all my tube amp newbie questions) I asked if this was an accurate way to put it (in simple non-tech terms).... If the amp is designed for 8 ohm load and you are running it with an 8 ohm speaker load the speakers are using 100% of the power that the primary winding of the transformer is refilling to the secondary winding of the transformer. Now if you run a higher speaker load like 16 ohms or more (or no speaker load), since the resistance is higher than the transformer expects to see the power leaving the transformer can't get out as fast because its path is restricted by the higher resistance/impedance. So now only 60% (for example- I'm just making up this number) of the power has been able to leave the secondary wiring of the transformer and there is 40% left in there. The primary winding of the transformer now refills the 100% it always refills to the secondary that still has 40% in it. Obviously the transformer was not designed to cope with 140% of it's design load. Over and over this repeats with power remaining in the secondary- and it keeps stacking hihgher and higher until it gets so overloaded and hot that the insulation melts and you get arcing and all that fun stuff.
Mike said this was a somewhat accurate way to put it in simple non-tech terms.
So that is my understanding of it. And I am definitely not a tech!
-StratMatt
If it's a tube amp, this is the worst case version of the above impedance mismatch and will destroy something in your amp's output circuitry really fast - probably your output transformer (NOT cheap to replace), and maybe more. Never, ever do this. I don't care what anyone else ever tells you, don't do this.
-Miles, prompted by Dave Moore's posts
Use the [highest impedance] tap. There will be a slight difference in the tone (a tad more low end) but that's not the reason to do it; the 16-ohm tap uses the tranny's entire output winding to transfer power to the load, unlike the 4-ohm tap which uses only a small portion of it. This minimizes thermal stress on the secondary. If you use your cabinet in stereo mode (two 8-ohm inputs) and run two wires from the amp, that's still a 4-ohm load, as the output jacks on your amp are in parallel. My rule for tube amps is: run the highest available impedance, if you have a choice.
-Lord Valve
To find the impedance of speakers in series, just add them, or (assuming they all have the same impedance) multiply the impedance times the number of speakers:
total impedance = impedance of 1 speaker * number of speakers
Example:
To find the impedance of 4 4-ohm speakers wired in
series, just multiply 4 (ohms) * 4 (speakers) = 16 (ohms).
To find the impedance of speakers
in parallel (assuming they all have
the same impedance) divide the
impedance of 1 speaker by the
number of speakers:
total impedance = impedance of 1 speaker / number of speakers
Example:
To find the impedance of 4 16-ohm speakers wired in
parallel, just divide 16 (ohms) by 4 (speakers) = 4 (ohms).
(The general formula for impedances in
parallel is more complex, but when they
are all the same, it simplifies to this
equation. NOTE: wiring speakers with
dissimilar impedances wil result in
different amounts of power going to the
speakers, which may not be what you want!)
If you have to parallel 2 impedances that are not the same, use this formula (where Z means impedance):
total Z = (Z1 * Z2) / ( Z1 + Z2)
Example:
To find the impedance of a 4 ohm cabinet wired in
parallel with an 8 ohm cabinet...
Z = (4 * 8) / (4 + 8) = 32 / 12 = 2.67
If you have to parallel more
than 2 speakers that don't have the
same impedance, the formula is this:
1
----------------
total Z = 1 1 1
-- + -- + -- ...
Z1 Z2 Z3
Example:
To find the impedance of a 4 speakers wired in parallel,
with 2 speakers being 4 ohms and two being 8 ohms...
1 1 1 1
------------- ------------- - - 4
total Z = 1 1 1 1 = 2 2 1 1 = 6 = 3 = - = 1.333
- + - + - + - - + - + - + - - - 3
4 4 8 8 8 8 8 8 8 4
You can just keep adding as many terms
on the bottom as you need. Fortunately,
most speaker impedance problems for
guitar amps involve only speakers with
the same impedance, so you can use the
simplified form above.
The above formulas work for speakers within a cabinet, combining speaker cabinets, raw speakers laying around the bedroom, whatever.
-Miles
Rich Koerner has an excellent set of packing instructions at http://timeelect.com/Shipin.htm.
This varies. Everyone has their preferences and stories, both good and bad. Your best bet is to talk with someone nearby who ships or receives a lot of items, and get their suggestions, and combine that with the suggestions of whoever you are shipping to or receiving from. Whatever you do, you should seriously consider insuring your packages.
About the same thing as adjusting a carburetor. How much current is
running through the output devices at idle. Whether it's tubes or
transistors some current is running through the amp with no signal -
having that dialed in correctly makes a huge difference in how the amp
responds to music.
-Ronsonic
Biasing is a way of balancing longevity vs. tone. turn the knob one way, the tone gets better and the tube life gets shorter. Turn it too far and the tube life gets really short. Turn it too far the other way and the tubes last a long time but the amp sounds crappy.
Other components can be compromised if the bias is way out of range.
$$$$ <-----------> TONE
^
Bias
-Dr. Nuketopia
How important is it for your amp to sound good? How important is it for your tubes to last a long time? How important is it to not destroy the output stage of your amp? Improper bias can affect any and all of these. If your amp sounds good and you've never biased it and you play it a lot, it may well be OK. But whenever you get a new amp (new to you), it's safest to have the bias checked.
-from many posts
No, only the output, or power tubes. Such tubes function rather differently than other tubes in an amp. The preamp and similar tubes do not need bias adjustments unless there is something wrong with the amp. However, if you swap the type of preamp tube, such as replacing a 12AX7 with a 12AU7, it's not a bad idea to check the bias. Not because of danger to the tube in this case, but to make sure the tube is operating at its best. OTOH, if you drop in a new tube like this and it sounds OK (it almost always will), you're safe.
You should bias them until they sound the best they can within their operating parameters. Generally this means the static dissipation should be at or below the maximum plate dissipation rating for Class A amps (and you'd better be sure they are Class A if you bias them this way!) or below 75% of that maximum for Class AB amps.
For more details, see the technical FAQ.
Not true. Always check the bias of any output tube when it's replaced.
Not necessarily. Many name brand amps come biased really cold from the factory. At least one factory uses a mass production method that only makes sense if you're biasing the amp really cold. So these amps will not sound anywhere near as good as they should until they've been re-biased.
Additionally, most mass-produced tube amps today come with tubes that vary in quality from "just OK" to "utterly abysmal". A brand new amp may well need a whole new set of tubes to sound good. This, of course, necessitates biasing the new output tubes.
When buying a new amp, it's a good idea to ask around or search the archives to see what others' experiences have been in this area.
If your amp has multiple output tubes, whether push-pull or single-ended, you should replace all of them at once. If you are gigging with an amp, however, you could have extra tubes matched to your tubes that are being used, so that if one broke or the filament burned out you could replace just one tube.
It's best not just to depend on a numbering scheme or color codes to match tubes. If possible, buy truly matched sets from a reputable tube dealer. In the long run you'll be happier.
Watts are watts. But a tube amp with a certain wattage rating will likely be capable of producing louder, pleasing music than a solid state amp of equivalent wattage.
For a more detailed explanation, check the technical FAQ.
``When I was a kid, I saved up my money and bought a Silvertone 2x12 100W solid state amp to replace the little portable tube PA my Dad gave me to play through. The other guys in my band were using a silverface Bassman and Bandmaster. My Silvertone could get pretty loud, but when push came to shove, the lower-powered Fenders came through, but my Silvertone sounded thin and weak, even when cranked up. When I asked my Dad (one of the top electronics techs I've ever known) his simplified explanation was that tubes and transistors amplified different sets of harmonics. I later learned that he was pretty much right on the money. The "experts" can argue all they want, but I maintain that the primary difference in the sound quality between tubes and transistors is the simple fact that tubes maintain and deliver even-order harmonics far better than transistors. Even-order harmonics support the fundamental note, and therefore are richer and more musical. Odd-order harmonics do not support the fundamental, and are (for the most part) musically harsh.
``Putting a solid state (transistor, digital, or what-have-you) amp up against tube amps is really an unfair match, as I learned with my Silvertone. Even with more than twice the RMS power, I couldn't compete with the rich tonality of the tube amps. The transistors just couldn't preserve and amplify the even-order harmonics. That's my story, and I'm stickin' to it!''
-Monte Barnett
A tube is a vacuum tube. A valve is the British term for a vacuum tube. Solid state means transistor, or chips such as op amps that are built from transistors. (Diodes may also be either tube or solid state). We sometimes refer to solid state as "silicon" or "sand", but solid state devices may be germanium based as well.
"Valvestate" is a Marshall marketing term to describe an amp design which has a solid state power section but the "characteristics" of a tube amp. Some of these actually include a tube or two in the preamp, but frankly, they don't come ANYWHERE close to the sound of an amp with a tube output stage.
Hybrid amps are available in two flavors: Tube output stage with solid state preamp (Peavey Deuce / Mace / early "Classics", MusicMan, etc) or ones with tube preamps and solid state output stages (some Marshalls, some Ampegs, Hartke, etc, etc) It's much cheaper (and more common) to build an amp with a tube pre than a tube power amp, however, IMO, you get a more "tubular" sound when you overdrive a tube output stage than if you saturate a preamp tube and amplify it in a Solid State power stage.
Some SS output stages are a bit more tubular in behavior than others. If the amp species "power MOSfets" in the output, it's a little (but not much) more tubey than if plain ol' bipolar transistors are used. Has to do with how the device responds when you get close to saturation (as well as differences in input impedance).
-Mike Schway
NOTE - Amps using solid state diodes as rectifiers are not generally considered hybrid amps, as they do not use the solid state devices in the signal path. Sunn amps using transistors in the tremolo oscillator circuit are usually not thought of as hybrids, for the same reason. Mesa/Boogies with 5 band EQ, on the other hand, are hybrid amps (if just barely) because the EQ circuit, using solid state components, is in the signal path.
-Miles
Sure. You may or may not like the sound, but there's no physical reason you can't do it. You may need different input and output connectors, or a Hi-Z/Lo-Z transformer to convert between your guitar cable and a mic input, and the speaker outputs may be a bit strange, but that's about it.
But some folks prefer to take the PA apart and build a custom guitar amp. Instructions are available at http://www.rru.com/~meo/Guitar/Amps/PA2Guitar/old2new.html .
Not such a great idea, unless you use something besides your stereo speakers, and/or compress the signal. Plus, you may not like the sound of it, unless you use a guitar preamp.
Stereo speakers are not made to handle the dynamics of raw music. Distortion may appear as square waves, which are close enough to DC to fry your speakers. There are several other issues which may also destroy your speakers.
A stereo is intended to faithfully reproduce the recorded material. A guitar amp is supposed to add tone. Recorded material is typically compressed quite a bit. Live guitar has far more dynamic content than most recorded material.
(The only way you are likely to really be happy with such a setup is using a guitar preamp for tone, and a compressor to save your speakers. At that point, you might as well buy a guitar amp!)
So while you can do it, it's generally considered a really bad idea to try to use your stereo as a guitar amp. That's not to say you can't, or that it might not work for you, or that it didn't work just fine for your third cousin in Montpelier. But we wouldn't do it. We don't recommend it. If you do, and something fries, we told you so.
-compiled from various posts on the subject
Technically, "amp" is short for amplifier - the electronics that amplify the guitar (or other) signal to the point it can drive speakers at useful levels (where "useful is in the ear and mind of the hearer 8^).
Cab is short for cabinet, which is a box containing the amp, speakers, or both. The cabinet is usually made of wood or a wood product, and may be finished with a natural finish, a fabric covering, or in rare cases, paint. (A new, tough, painted on "fabric" is also possible.)
You can have a speaker cabinet or a combo cabinet with amp and speakers. You can even have an amp head cabinet. You decide what is really meant from context. Usage probably breaks down like this:
90 - 95% : speaker cabinet 5 - 9% : combo cabinet .1 - 1% : amp head cabinetBut when musicians use the term "amp", it may mean an amp head (just the amplifier in a box), or a combo (amp plus speakers in a box). It can't legitimately mean just mean a speaker cabinet (box with speakers in it). I'd guess that most guitar and bass players, when they refer to an amp, mean a combo - a cabinet with an amp and speakers in it.
These are speaker configurations for speaker cabs or combos (see above). The number before the "x" is the number of speakers involved, and the number after the "x" is the size of the speakers (diameter). The "x" is pronounced as if it was the word "by"; 4x12 is pronounced "four by twelve". Some common, and some not so common, configurations are:
1x6: Danelectro Cadet, Silvertone Amp-in-case
1x8: Fender Champ, Electar 10
1x10: Kalamazoo Model 1, Model 2, Reverb 12
1x12: Fender Deluxe Reverb, Peavey Classic 30, Fender tweed Deluxe,
Gibson GA-12, Crate CR-1 (original crate)
1x15: Fender blackface Vibroverb
1x18: Ampeg B-18 Portaflex
2x10: Gibson GA-79RV Stereo
2x12: Fender Twin, Vox AC-30, Lab L5, Peavey Heritage,
Silvertone 1484, anything with 212 in the model, etc.
2x15: Fender silverface Bassman, Kustom 200
3x10: Fender narrow panel Bandmaster
3x12: Kustom 200
4x10: Fender Super Reverb, 1959 Tweed Bassman
4x12: Fender Quad Reverb, cabs by marshall, Boogie, Crate,
Peavey, Carvin, HiWatt, Orange, you name it
6x12: Sunn Sentura
8x8: Wards Airline GDR-8518A
8x10: Ampeg SVT, Marshall cab
A stack consists of two 4x12 speaker cabs, one on top of the other. This was popularized by Marshall during the 60s. One 4x12 cab by itself is a half stack. Some manufacturers produce 2x12 cabs; these are sometimes called quarter stacks if and only if the speakers are mounted side by side in the cab.
There are two reasons a bottle (!) may glow blue.
Have a careful look. If there are patches of blue glowing on the glass, probably with fairly sharp edges, it's due to electrons missing the anode and hitting the glass instead, making it flouresce. (Most of the tube envelope may even glow. -ed) Quite pretty, and you can play for hours, moving the patch with a magnet... (Don't electrocute yourself!) This kind of glow is common with beam tetrodes and is completely harmless. (This type of glow is by far the most common. -ed)
However, if there is a fuzzy blue glow in the space in the bottle (inside the plate, or streamers coming out -ed) it's due to traces of gases in what should be a vaccuum. The valve has gone soft. Bad news for the valve as ions will bombard the cathode, shortening its life. Also, the trace of gas can break down leading to an internal arc. A soft valve set will sound slightly different, especially in amps without feedback, as the presence of ionised gas affects the transconductance and secondary emission. (This is fairly rare. -ed)
-HTH
For additional information, see the Blue Glow in Tubes FAQ at
http://www.rru.com/~meo/Guitar/Tubes/blue_glow.html
or a couple of documents transcribed from old tube manuals at
http://barney.webace.com.au/~electron/tubes/blueglo.htm .
This is not only normal, it's a requirement of tube operation. This glow normally comes from the tube's heater, or filament, which heats the cathode so that the tube conducts properly. If you don't see this, and your amp doesn't seem to be working properly, check the amp in the dark (some tubes, esp. Sovtek 12AX7LPS tubes) have a filament glow which is very difficult to see. If you still aren't sure, let the amp warm up for a few minutes. Then, place a fingertip near each tube in turn. If the tube is not hot, the filament is burned out and you need to replace it.
NOTE - be careful; even a brief touch to a hot tube can burn you badly enough to cause blisters.
First, read the orange glow question above. Is the color you're seeing orange, coming from the top and bottom of the tube's "guts"? If so, you're OK.
BUT... if the plate, or any part of it, especially in a power tube, is actually glowing red (even a faint red) shut the amp off at once and find out what the problem is. Otherwise, you will certainly destroy the tubes. You could also destroy other parts of your amp, resulting in a huge expense to repair it. Take the amp to a good tube amp tech, or start asking question in AGA, if you think you want to learn how to work on things yourself.
For 6L6 tubes, try http://divine.EECS.Berkeley.EDU/~loarie/blues.html . For 12AX7/ECC83/7025 tubes, try http://12AX7.freeyellow.com/tubeID.html .
Vibrato is a modulated (up and down) change in pitch, such as you get when you wiggle your finger on a fretted string, or when you wiggle the whole neck or play with the whammy bar. Tremolo is a modulated change in volume, as if you were turning your amp's volume up and down quickly. Tremolo is common in surf music; vibrato is common in rock and blues.
NOTE - be careful when using these terms. Some people use them backwards to this, and some people use them interchangeably. In fact, Fender is responsible for a lot of the confusion, calling the whammy bar a tremolo bar, and calling the tremolo on their amps vibrato. To be fair, even dictionary definitions can be vague, although the primary definitions in most dictionaries will at least lean towards the definitions here.
This confusion is why many people refer specifically to "pitch vibrato". But then how do you refer to tremolo? "Volume tremolo" sounds stupid!
Oh, and please note the spelling. It's tremOlo, not tremElo.
-Miles
Your amp almost certainly has tremolo. Tremolo is much easier to achieve. While various claims have been made over the years, we're not aware of any guitar amps with true vibrato. This includes Magnatones and Fenders with "Vibr" as the first part of their name.
Gerald Weber states in his Desktop Reference of Hip Vintage Guitar Amps that some Fenders have true vibrato. This is incorrect. If you believe you have a Fender schematic showing otherwise, please send us a copy; we'd love to see it!
The people maintaining the Magnatone web site claim that Magnatones had true vibrato. We've been told by a reliable amp tech with Magnatone experience that some Magnatones really do have this.
A Leslie or similar rotating speaker produces a pitch shift that's somewhat like a vibrato. But rotating speakers are not very common in guitar amps. 8^)
Caveat: It's entirely possible that some digital modeling amp (or even a very sophisticated solid state, analog amp) has this capability. But we can't find evidence of any tube amp or solid state analog amp with vibrato. If you have any such evidence, please send it our way!
-Miles
For the most part, it's cheaper to buy. Especially if you buy used. Especially if you've never done this.
The cost of building a small amp you can get for $100 used is double that or more - not counting labor.
I don't know that the cost would be double at the 100 watt level, but I would be very surprised if you could build as cheaply as buying, unless you are very good and/or lucky at scrounging, and know what you are doing, or have someone willing to put in a lot of time educating you. Because just one wrong part could fry a bunch of others and set you back a bunch.
If you buy used, you may need to work on the amp. This will bring the price up. But unless the amp is in horrible shape, it will still be cheaper than building from scratch, or even most kits.
On the other hand, building an amp is a great way to learn about them. And when you've built one, you will know that amp inside out. So the benefits may outweigh the cost; only you can decide.
-Miles
If your amp is equipped with a STANDBY switch, there is only one correct way to use it. DON'T flick both the POWER and STANDBY switches on (or off) at the same time, or leave the STANDBY switch permanently in the "operate" position while using just the POWER switch. When you turn your amp's POWER switch on, make sure that the STANDBY switch is in the "standby" position. A STANDBY switch interrupts the high voltage supply to the tubes; when the amp is on "standby," only the tubes' filaments have voltage applied to them. When you turn the amp on, leave it on "standby" for at least five minutes...ten would be even better. This allows the tubes to warm up gradually; the tubes can take the high-voltage surge when the STANDBY switch is moved to the "operate" position much better when they are warmed up first. After the STANDBY switch is placed into the "operate" (or "playing") position, it will still take the power tubes several more minutes to reach full operating heat. It won't hurt anything to play the amp while the tubes are still not all the way hot, but the amp won't sound as good as it can until the tubes reach full operating temperature.
If you're playing a gig, DON'T PUT THE AMP ON STANDBY DURING THE BREAKS! Once it's hot, LEAVE it hot! Putting the amp on "standby" every time you leave the stand just thermally cycles the tubes (hot/warm/hot/warm etc.) all night long; this causes expansion and contraction of the internal parts, and this is one of the ways that tubes wear out. If you're worried about your guitar feeding back while you're on a break, just turn the guitar's volume control all the way down before you lean it against the amp or place it in its stand. When the gig is over, put the amp on "standby" and let it cool down for five or ten minutes before you turn it all the way off.
-Lord Valve's famous diskette files
Leave the controls zeroed (turned all the way down) while the amp warms up. Tubes can make some strange noises as they heat; popping, fizzing, crackling, creaking, etc. These sounds may be alarming, but they are quite normal. Let the amp warm up for five or ten minutes before you play anything through it.
-Lord Valve's famous diskette files
The amp may have been designed not to need one. Many smaller amps with tube rectifiers have tube complements that work fine in these situations. If your tube amp has a solid state rectifier, though, you may wish to have a standby switch added, especially if the amp seems to eat tubes.
(from various postings)
It doesn't need one. Turn it on. Play guitar. Turn it off when done. That's it.
-Miles
As long as it's not a HUGE speaker-eating pop, it's ok and although not perfect, within the range of "normal".
This is just an educated guess, but I think what's happening is that when the power is turned off, you have a temporary imbalance in the positive and negative power supplies as the filter caps discharge unequally. In the few milliseconds where there still is some charge, the amp is imbalanced and lil' instabilities can develop resulting in audible oscillations. Eventually the caps discharge to the point where the equipment no longer can amplify the oscillations. In your case, anywhere from 1/10 of a second to a full second or so. The result is an audible chirp or squeal.
--Mike Schway
There's a bird trapped in your amp. I don't like birds cause they poop on my car, that's just cruel. Try luring him out by spreading some sunflower seeds in the back of your amp.
-Pete (PMG)
This is usually due to arc'ing across the switch. You may need a switch with a higher current rating, or with a standby switch, higher voltage rating. This is not unusual and generally won't hurt anything (other than the switch, which will probably wear out faster.)
Yes. If you're worried about the amp's value to the insane collectors who even worry about whether the dust is original, keep the old cord and the "death cap" if any. But do the work or have it done. This can save your (or someone else's) life.
If you're good with a soldering iron and are aware of the safety issues (poking around in an amp can hurt or kill you!), it's one of the easier mods to perform. But it must be done right, or you could be closer to death than you were before. You can read up on the safety issues and the conversion itself at http://www.rru.com/~meo/Guitar/Amps/Kalamazoo/Mods/safe.html .
You never need to form new caps. The only caps that need forming are older electrolytics in amps that haven't been played for some time, and NOS electrolytic caps that have been on the shelf a long time. These caps should be brought up slowly on a variac. If you have just bought an old amp you suspect hasn't been played in a while, take it to a tech and have this done. If you expect to need to do this more than a couple of times in the next few years, do some research and get a variac, and learn how to do this. It's not hard, but there are things to consider (such as filament voltage).
Power attenuators are devices used to reduce the amount of power going from the amplifier to the speaker. As opposed to a volume control on an amp, attenuators are almost always external, outboard devices. Some examples are the THD Hotplates, Scholz Power Soak, Marshall Power Brake, Altair units, and Rocktron Juice Extractors, among others. People use power attenuators because they like the way an amp sounds when turned up loud, but don't need all that volume, and don't wish to buy another lower-power amp as a solution.
-Mark Taylor
There are, however, a few modern, boutique amps (the Aiken Invader conmes to mind) with built-in attenuators.
Despite many discussions, there has never been and probably never will be a consensus on AGA about whether they are a "good idea" or "bad idea".
-Mark Taylor
Rich Koerner calls them "tranny toasters", and suggests they are as ``functional as having put training wheels on a top fuel dragster to slow it down till you get the feel of the thing on city streets to go food shopping and not wake sleeping dogs whose bark will be louder than that dragster's newly tuned exhaust pipe's wimpy sounding tone.''
We've yet to find a proponent with as elegant a description. If we find one, we'll include it.
-Miles
AGA summary: No consensus; Although it's probably safe to say that they're not good for your amp there are too many variables - ``Which device? Which amp? How healthy is the amp to begin with? How hard are you driving the amp/cutting back the volume?'' - to answer this with an meaningful "yes" or "no". For every amp tech saying - essentially - "You're crazy to use one of those things", there is another tech saying "Not necessarily so" There are always a number of "I've used them for years without a problem" posts for each blown transformer anecdote.
-Mark Taylor
No consensus. THD Hotplates seemed to get the most consistently positive comments, with the Power Soaks coming in second.
It seems as though the players reporting the best results with p.a.'s were those who only moderately attenuated the amps. Generally, the more you cut the volume back the more tone you lose. So trying to take a dimed head down to line/headphone level isn't likely to be your best-sounding setting. If you find that you really do need very low/line levels and all you have is that 100 watt head, then you might want to look at another solution like a smaller amp or a POD or whatever.
-Mark Taylor
Yes. They all do, to a greater or lesser extent. The net effect is not necessarily good or bad, it all depends on the amp / attenuator / speakers and how you're using them.
-Mark Taylor
On some amps you can pull 2 of the 4 output tubes and cut the power roughly in half. Some devices like Yellowjackets allow you to substitute power tubes which can result in a different tone and lower output power. Using a Variac (technically a kind of power attenuator), you can lower the voltage going into the amp and in so doing lower the output volume at a given setting. (NOTE - this can be extremely dangerous to your amplifier. -ed) Don't overlook what you can do with a couple of heavy blankets over your speaker cab, that can cut your volume way back, and by playing with how much speaker is exposed vs covered, you can compensate for the damping effects of the blankets. Works great with mics. Cheap, safe and reliable, too. (NOTE - Don't block ventilation to your tube amp, or it may fry. Consider putting the amp in another room or building or buying an isolation cabinet. -ed)
-Mark Taylor
Or just buy a smaller amp for those low volume situations!
-Miles
Yes, but make sure you pull one from each side of the output transformer. Otherwise you will just have a mess. Since this changes the output impedance, you'll need to adjust either your output impedance selector or your speaker load. Here's the deal on that:
When you have 4 tubes in a push/pull amp, that's two tubes in parallel per alternation of the sine wave. When you have 2 tubes whose plates are in parallel, the plate impedance (which is what the output transformer "sees") is halved compared to a single tube per alternation. (Just like speakers, when you have 2 8 ohm speakers in parallel, the total load is 4 ohms.)If you don't have an impedance selector on your amp, you should adjust your load such that if you're running 4 ohms, f'rinstance, with 4 tubes, you should be running into 8 ohms with 2 tubes. The actual load under 50W conditions is twice that specified by the normal 100W output tranny.
If you don't change your speaker impedance, you need to adjust the head's impedance such that the speaker load is 2X what the 100W load would be. In the case of an 8 ohm cabinet, you need to select a 4 ohm output impedance on the amp. (8 ohms is twice what the amp thinks it should be running.)
-Mike Schway
Though the rated power and the relative loudness of an amplifier are directly proportional to each other, one is not an exact indicator of the other for many reasons. The two we will cover here are which power rating is actually used, and how efficiently that power is delivered through a speaker.
Manufacturers have through the years resorted to different ways of expressing the power ratings of their amplifiers. From a marketing stand point, big numbers sell products.
For example, a Fender Twin Reverb could be classified in any of these ways:
100 R.M.S. and/or Continuous watts 150 E.I.A. watts 220 Peak Music watts 250 Pulsed Program watts 500 Peak watts 1000 Peak to Peak wattsNotice, these are all ways to put a "different" number in front of the word "watts", and yet they indicate the same thing with respect to the relative loudness of the Twin Reverb amplifier. So now you can see that not all "watts" are the same, unless "specifically" stated by the manufacturer. (In fact, they should also designate a frequency range and maxiumum distortion value and type. For most discussions on AGA, people are assuming the typcial guitar frequency range and negligible values of distortion. Some people allow lots of distortion, though, so it's still slightly nebulous. -ed)
To me, amplifier output performance stated in terms of R.M.S. watts is the only meaningful number to accurately represent the power level of a sine wave. That sine wave is the basic of all musical vibration. That basic can be found in the sound of the flute, the fundamental vibrating note of the guitar string, the note produced by the Hammond B3, the Rhodes piano, the acoustic grand piano, etc.... and is common to most all natural musical melodic instruments.
So now we have a standard for what comes out of the amplifier only. There is still the working relationship that the speaker plays in the reproduction of the sound from the amplifier. The efficiency/sensitivity of the speaker's ability to convert electrical energy in to sonic/sound energy in the air for the ear to hear is now the heart of the matter.
This sonic energy in the air is measured in terms of Sound Pressure Levels using an SPL meter. This is a calibrated meter that hears what you are hearing at the same time, and tells you exactly how loud the sound is in decibels (standard units for measuring sound levels).
The rated efficiency of a speaker is commonly determined by placing a 1,000 Hz sine wave at one watt on the speaker and measuring the speaker's loudness 1 meter away with an SPL meter.
Now, let's connect the dots, and put this all together. We have two Twin Reverbs that perform identically. One Twin Reverb has a set of speakers with a sensitivity rating of 101 db, and the other Twin Reverb has speakers with a sensitivity rating of 90 db.
The Twin Reverb with the 101 db rated will be much louder than the other Twin Reverb for the same amount of power output delivered to the speakers.
Now it can be seen that the efficiency/sensitivity of the speaker plays a major part in exactly how loud an amplifier is going to actually be.
-Rich K.
I found this info somewhere on the web and found it very useful.
Relative to the standard amp power of 50 watts:
X% louder = 2^log10(P2/P1) * 100%
40 watts is 94% as loud as 50 watts. 30 watts is 86% as loud as 50 watts. 25 watts is 81% as loud as 50 watts. 22 watts is 78% as loud as 50 watts. 20 watts is 76% as loud as 50 watts. 18 watts is 74% as loud as 50 watts. 15 watts is 70% as loud as 50 watts. 12 watts is 65% as loud as 50 watts. 10 watts is 62% as loud as 50 watts. 9 watts is 60% as loud as 50 watts. 8 watts is 56% as loud as 50 watts. 7 watts is 55% as loud as 50 watts. 6 watts is 53% as loud as 50 watts. 5 watts is 50% as loud as 50 watts. 4 watts is 47% as loud as 50 watts. 3 watts is 43% as loud as 50 watts. 2 watts is 38% as loud as 50 watts. 1 watt is 31% as loud as 50 watts.
-Magic Twanger
"Ruby" on the glass does not mean Chinese. Ruby sells tubes from JJ/Tesla, China, Russia (both Svetlana and Sovtek), Yugoslavia, etc. Unless you know how to eyeball the guts inside the glass, you don't know what Ruby's tubes are. Ruby is a good, honest outfit, and one of the few that cares about quality control. The numbers on their power tube boxes actually mean something, too, unlike a couple of other outfits I could mention. Furthermore, as far as I know, the Chinese don't make EL-84s. At any rate, I've never seen one.
-Lord Valve
Please see the Sources FAQ at the AGA web site at http://aga.rru.com/ .
Please see the Sources FAQ at the AGA web site at http://aga.rru.com/ .
The definitive site is at http://www.timeelect.com/400-PS-IDX.htm . There's also a mailing list there.
The original 6L6 had a metal tube. Later 6L6s had a suffix beginning with a "G" to indicated the tube was made of glass. There were several of these:
6L6 - metal cased tube, a black mild steel cylinder 6L6G - same tube in a sexy glass ST14 shape "coke bottle" 6L6GA - smaller bottled version of 6L6G 6L6GB - small straight sided glass 6L6G 6L6GC - more powerful version of 6L6GB
There was also a 6L6WGB, which is allegedly a militarized (more rugged) version of the 6L6GB. And there's the 5881, which is also a militarized version of the 6L6GB, but with a slightly higher power rating (23 watts static dissipation vs 19 watts for the 6L6GB). And there are 6L6WXT versions floating around as well. Several noted AGA techs have successfully used 6L6WGBs in amps that push 6L6GCs fairly hard.
Where it gets weird is with newer tubes. Groove Tubes has its own set of suffixes (B for GB, C for GC, and some comepletely new ones). They also sell a "higher powered" coke bottle version, the 6L6CB. Then there's the 6L6EH, which is Electro-Harmonix's version of the 6L6GC...
More details are available in the technical FAQ.
Not quite! You can substitute freely between the 6L6, 6L6G, 6L6GA, and 6L6GB. You can use a 6L6GC in place of any of these. You should not use any of the lower rated tubes in an amp designed to use the 6L6GC tubes. Doing so will most likely fry the new tubes. At the very least, you can expect drastically shortened tube life. 6L6GCs are designed to handle better than 50% more power than the other 6L6 tubes. For newer tubes (see above) check with whoever you buy them from.
Make sure whatever tube you are going to use can handle the voltage in your amp. Some newer tubes will not last as long in amps that ran voltages beyond the tube ratings, whereas many NOS tubes would survive well beyond their rated maxiumums.
You can find more information on 5881s and 6L6s at http://www.jt30.com/jt30page/micKtubes/What-is-5881.html. <
[Thanks to dr wow for that link!]
Nope. You probably won't try this more than once. The cable between your guitar and amp (or effects) has to be shielded to prevent picking up noise (electromagnetic radiation from lights, motors, radio, etc). If you use unshielded cable (such as 99.9999% of all speaker cable) this noise will get amplified and drown out your guitar signal in a horrible flood of sonic mayhem.
Not a good idea. It might work for a while, but it's risky. Especially if you are pushing high power through a cable with a small center conductor, you risk either an open circuit when the conductor dies, or more likely melted insulation as the inner conductor gets hot, resulting in a short circuit. Neither is very good for your amp. Also, the additional capacitance in the cable will adversely affect the impedance your amp sees. It will degrade your tone at the least, and may make your tubes and other components wear out faster as they have to work harder.
I would suggest searching www.deja.com and see what the various comments have been. Go to http://www.dejanews.com/home_ps.shtml and enter "alt.guitar.amps" as the forum, with "Dan Torres" as the keywords. You'll find a number of people's experiences and opinions there.
Joint Army Navy -- tubes selected for their ability to withstand the shock & jarring of '50s/'60s military equipment with a lower than average failure rate.
-David R. Bucholz
You can find lots of information on this topic at http://www.kropla.com/electric2.htm . Thanks to Bill Kahle for pointing out this link!
That depends on what you want to do. If you are happy with the sound of your amp, and it has Groove Tubes, you can drop in a "matching" GT set and have a good chance things will sound fairly close and not blow up. On the other hand, there are alternatives (see next question) you may wish to consider. Groove Tubes works hard to select and match tubes, but the fact is that tubes that test the same may sound different, and replacing output tubes without rebiasing always carries a certain amount of risk. GT can reduce that risk, but never eliminate it entirely.
Certain older tubes are among the best tubes ever made. Most tubes produced between the early 1970s and late 1990s varied a lot in quality, to say the least (some were known as firecrackers, because they tended to go off with a bang, very quickly!) However, some of the tubes being made today are quite good. So the best tubes tend to be either NOS or pretty recent.
It's not as simple as dropping in any, random NOS Tube. Some of the NOS available is junk. Some of it's rejects, forgeries, even worn out tubes that have been cleaned up on the outside. Some of the NOS available is still the best you can find at any price. If you don't know what you're doing, find someone who does who can help out. Buy only from reputable dealers and educate yourself as you go.
Whether you should use NOS tubes, only you can decide. Keep reading to help make that decision.
In a perfect world, you could walk into any music store and say, ``I want to sound like [whatever]'', and a light would come on in the air above the head of the person behind the counter, and they would rummage around and produce exactly the tubes you needed. Free. Because they would be independently wealthy, doing this as a labor of love.
But the reality is, that to get the right tubes, you either need to try lots of tubes yourself, or have a tech you can work with to get the sound you want. This is even true with NOS. And you generally have to pay for them.
Ideally, you want tubes that have been tested. Even NOS tubes should be tested, since what's left includes a lot of rejects that should have been thrown away, and despite some factories' excellent quality control, there were still some duds. Most people also want reasonably matched output tubes, if only because it makes biasing easier. I can't stress enough that until you know what you are doing, you should only buy from a reputable dealer. You can find some of these by searching the alt.guitar.amps archives at http://groups.google.com/advanced_group_search .
Testing-wise, for guitar amp purposes, it's not sufficient to find an old tube tester and see if the tubes register "good". You want tubes that will hold up under your voltage and current conditions (i.e., those found in your amplifier), tubes that are not excessively microphonic, tubes that will last, tubes that sound good. This requires a variety of testing, and most top tube vendors go through a lot of tubes finding the best ones. They will also be able to help (to an extent) with the tone of the tubes.
Some folks will tell you that a certain brand of a certain tube will always sound or perform a certain way. This just isn't true (that dratted imperfect world!) Certain tubes of certain brands will hopefully be similar, but while some fall into a narrow range of tones and specs, others are all over the map. Again, it helps to have a reputable tube vendor who really knows their stuff. Also, you can search (see google above) the alt.guitar.amps archives, and look for online tube taste tests such as those at http://www.rru.com/~meo/Guitar/Tubes/ .
And, yeah, you gotta pay for them.
Absolutely maybe. Feel better?
In general, you probably want matched output tubes. (Hi fi folks like matched preamp tubes, but most guitar amp folks don't care about that.) Matched tubes mean they will all draw the same current under the same conditions, at the very least. This yields the most uniform waveforms, makes biasing easier, and is generally easiest on your output transformer and tubes.
On the other hand, unmatched tubes can produce distortion sounds that some people like. If this is the case, great - just realize that to keep that sound, you'll need to match any new sets of tubes to your current set, instead of to each other, per se.
-Distilled from several, huge, flame wars.
Now there's a thermonuclear topic! There are a variety of opinions. Here's one take on it.
``Tubes can be matched in two operating conditions. "Static" matching is where the tube has its bias set, and there is no signal applied to it, and the tubes are matched to setup equally in this no signal condition only.``Then, there is dynamic or mu matched tubes, where the tubes are matched for equal performance when signal is applied. Again, the voltages for such testing and matching should be a good representation of what the tube will find in your amplifier.
``Many today feel that dynamic, or mu, matching is not necessary. Yet, a set of tubes can be "matched" at their bias setting, and be "not matched" when signal is applied to them. A good set of static matched tubes may result in one tube clipping well before the other tube does when your sound goes through the tubes. This is what dynamic, or mu, matching should prevent. Do not assume the term "matched" means both of these operating conditions.''
-Rich Koerner
If it's a tube amp, you should be safe. It varies with solid state amps, but in general, find out what the manufacturer recommends as a maximum signal input and stay below that.
The cap is there to provide signal coupling between earth and chassis ground. You want the chassis to be referenced to earth ground and not to float in order to shield stray RF. This coupling is achieved not by hard wiring, but via a .02-.05uF/400-600V capacitor.
The neutral (white) 120VAC wire is grounded at the service panel (fuse box to old-timers). In the (bad) old days of nonpolarized 2 conductor plugs, you had a 50% chance that a particular AC leg would be the one which was grounded. That's not particularly good odds. Hence the selector switch which would connect one or the other leg to the chassis-coupling cap. If this cap becomes electrically leaky, you have a 50% chance that the chassis will be energized @ 120VAC. Thats why you get shocked when you touch chassis on some old equipment. If the cap is in good shape, then there would be no problem if the switch is in the wrong position, other than some additional hum. Old caps (especially the wax/paper ones) do become leaky in time and act more like low value resistors than caps. OUCH!
With a 3 wire plug, you now have a real connection from chassis to ground via the green wire. No way to mix it up, unless the venue's service is miswired. Thus, there's no reason to keep the old grounding cap.
-Mike Schway
Tech Head response: Nuke the radio station?
Seriously, try some ferrite beads especially near the jack socket on the amp. If it's on a PCB, then it's more difficult.
You said that one of your effects units when kicked in made more difference, try some beads on the interconnecting leads themselves. You will need to unsolder the live and ground wires within the jack plug, slip a bead on each and solder back. This includes the lead from the instrument to the first FX box.
If that fails, you need to start soldering capacitors across things to get rid of it. I had a Laney 100W transistor head which was great at this time of year between 6 and 8 PM. Sadly, it couldn't decide between Voice Of America and the BBC World Service which are both devoid of interesting latin beats to play along with.
It's all fixable - all you need is a little patience and some time to experiment to find out the real source of the problem.
-Duncan Munro
This is covered in Lord Valve's Tech Tip on "Fixing Noisy Pots" on the AGA web site.
The best cleaner is made by Caig Labs. Pro Gold 100 is the best control cleaner, followed by Pro Gold 5. Spraying excessive cleaner into controls can strip out the lubrication and will sometimes cause the control to sieze. Calilube is the best spray lube for pots not slide faders.Preserve-it is another good lube for pots. When cleaning slide faders first use a control cleaner, then a lubricant. The best lube for slide faders is silicone grease. Silicone grease can be bought at the scuba store in a jar and is non toxic food grade silicone. load some into an industrial syringe and squirt it into the mechanical surfaces of the slide fader. Spraying cleaner into a slide fader (dont use relay cleaner) can lock it up! There are alot of cleaners for pots but they are not as good as the Caig Labs products they wont last as long. A small can of PG 100 is $29.00.you get what you pay for!
-Michael Friedlander
Never use WD-40 or anything similar. It's a combination solvent (dissolves things) and oil (not a good conductor). Neither is quite what you want inside your pots.
-Miles
Radio shack cleaner is mineral oil. Ever pay $7 for an ounce of mineral oil? Now you have! What's the voltage rating of mineral oil?
-Michael Friedlander
(IOW, don't use mineral oil! -ed)
(all together now) Do you recognize the tune?
If it's an older tube amp, or just one that hasn't been played in quite a while, it may need the power supply capacitors replaced. Beyond that, here's a good, solid post on debugging amp hum; it was in response to smoeone in a country using 50HZ power; you may need to think 60 instead of 50 and 120 instead of 100, depending on where you are.
Plug the amp in, turn it on, set all the controls on your amp and your guitar to normal playing position. Hum, right? OK, reach over to the amp and yank the guitar cable out of the input jack. Does the hum go away? If it does, it's your guitar, or your guitar's proximity to the amplifier, which throws a 50 Hz field out to a distance of several feet; if your pickups are located within this field, they will couple the 50 Hz signal into the amplifier's input. Does the volume or character of the hum change when you move the guitar relative to the amplifier? If so, the cure is distance. Move away from the amp. Many bedroom jammers sit next to or even on top of their amps; this will often cause the problem you're having, especially if your guitar has single-coil pickups.
If the hum doesn't go away when you unplug the guitar, you'll have to look inside the amp for the problem. Does the reverb control affect the volume of the hum? Try repositioning the spring tank; the recovery transducer may be picking up hum from the power transformer. Wrapping the tank in aluminum foil sometimes helps, too. Experiment with poking leads into different positions inside the chassis; you may find that a certain lead arrangement makes an improvement. Is the hum just as loud with the volume control all the way down as it is with the controls in playing position? This points to a power supply problem, although this particular kind of hum should be at 100 Hz, not 50. The extra smoothing capacitor you've fitted can't solve the problem if it's caused by all of the factory-fitted capacitors being defective. Check them. Also, make note of whether certain controls on the amplifier (equalisation, reverb, volume, etc.) affect the volume or tonal character of the hum; this may provide a clue pointing to the portion of the circuit where it is originating. As a last resort, remove the mounting bolts from the power transformer and try re-positioning it; the field it throws may be coupling into the audio circuitry, and a change of orientation may help.
-Lord Valve
Before you get inside the amp, also try moving the amp around, re-orienting it, using a different outlet, going to another room. The problem may be grounding or shielding, and an environment with a lot of power noise in it will aggravate the problem.
-Miles
The hum balance control is used for cancelling out hum that is generated INSIDE the amp, not for hum picked up from the OUTSIDE
(i.e. via a guitar's pickup or wiring).
The basic idea:
- Chris Mohrbacher
Lord Valve wrote the following about Fenders, so just ignore the part about setting the bias balance control if you don't have one of those.
The "OUTPUT TUBES - MATCHING" control is a bias-balance adjustment. This is easily set by anyone who owns a screwdriver. First, you will need to adjust the other control on the back panel, the "HUM BALANCE" control. Adjustment of these two controls is very similar; they do completely different things inside the amp, however. To adjust the HUM BALANCE control, plug your guitar into the amp, turn all the controls on the amp and the guitar to the settings you normally use when playing, and then turn the GUITAR'S volume control all the way down, leaving it plugged into the amp's input. Insert a flat-blade screwdriver into the adjustment slot in the HUM BALANCE control and "tune" it back and forth...you'll find a place where the hum you can hear in the speakers is the softest; that's where to leave the control set. Note that it's a good idea to do this in a *very* quiet room, say at three in the morning. If you can't stay up that late, disconnect your speaker cabinet and plug a set of headphones into the speaker output jack; since the headphones are stereo and the amp is mono, you'll only hear sound in one earcup. BE VERY CAREFUL not to play any notes on your axe while you are wearing the headphones, or you will blow your brains out through your nose. (LOUD!!) Once you have the HUM BALANCE control set for the lowest possible hum, you can move on to the OUTPUT TUBES-MATCHING control. For this one, turn ALL controls on the front of the amp to ZERO, and adjust the OUTPUT TUBES-MATCHING control for minimum hum, just like you did with the HUM BALANCE control. You may want to take another shot at adjusting the HUM BALANCE control, because the hum you just nulled with the OUTPUT TUBES-MATCHING control may have been masking some of the hum when you adjusted the HUM BALANCE control. You may need to go back and forth between both controls a few times before you arrive at the quietest setting. Note that you must pay attention to the instructions (above) regarding settings of the front panel controls and guitar controls EACH TIME you adjust the rear controls...all zero for the OUTPUT TUBES-MATCHING control, and all in normal playing position for the HUM BALANCE control. If you find that you cannot null all (or most) of the hum from the output, you may need a new set of power tubes. Consult a technician for this; you may also have a fried HUM BALANCE control, and that's a sign that one or more of your power tube sockets have arced. The HUM BALANCE control is a 100-ohm pot which is connected across the 6.3 VAC filament supply, with the wiper grounded. It helps null 60 Hz hum out of the preamp circuitry. The OUTPUT TUBES-MATCHING control helps balance the DC current levels in the output transformer primary, and aids in removing 120 Hz power supply ripple from the output stage.
-Lord Valve
Actually, the reason for having the guitar cable plugged in is because in some amps, there is a switching contact in the jack which engages another tube stage, or turns something on (or whatever) that wouldn't be operating without a plug in the jack. If the guitar's turned all the way down, the tip is shorted to the sleeve anyway, so the cable is effectively not there as far as the amp's input stage is concerned. Just the physical presence of the plug in the jack is what I'm aiming for.
-Lord Valve
You might try it with and without the guitar plugged in. Also, if you use the headphones as LV suggested, (a) heed the instructions not to touch the guitar while playing if you value your ears and (b) for tube amps these should be low-Z headphones (4 or 8 ohms).
-Miles
You're measuring the DCR (DC Resistance -ed) of the primary and getting around 300 ohms plate to plate. Sounds good. You'll never measure the P-P load (around 8k for a pair of EL84s) as it is the reflected impedance with the secondary loaded. If you don't see physical signs of the OPT being fried (burnt, melted, stinky...) try this:
Impress a low AC voltage across one winding and measure the AC voltage across the other. This is out of circuit, no load attached, etc. The impedance ratio is the square of the voltage ratio. So, if the OPT is designed for 8k primary and 8 ohm secondary, that's 1000:1 impedance ratio. sqrt(1000) = 31.6 -- this is the expected voltage ratio. So 6.3 VAC across the full primary should give about .2 VAC across the secondary. Going the other way, 6.3 VAC across the secondary yields about 199 VAC across the primary. You don't expect to draw much current at all doing this, so fuse the AC fairly light and if the fuse pops, the OPT is shorted. If the fuse doesn't pop, the OPT could still be shorted internally. Some turns could be shorted, and the voltage ratio should show this.
If it doesn't show physical signs of being cooked, and the voltages check out OK, it's probably a good tranny.
Gary Gerhart
Normally in a tube amp, you are dealing with a positive voltage (B+) with reference to ground. But with a bias supply, you are dealing with a negative (C-) reference to ground. Ground is just a handy reference when it comes to voltages - remember that you can have AC ground, signal ground, and PS ground - and they're all usually the same ground!
-Miles
These letters once refered to battery classes for circuits. (You'll notice that tube texts generally show batteries as power sources for the various DC voltages - they meant it!) A batteries were for the heaters (filaments). B batteries were for plates and other (relatively) high voltage supplies such as screen grids. C batteries were for control grid bias supplies.
The B voltage is positive (B+). The C voltage is generally negative (C-). The A voltage polarity generally doesn't matter, but if it's DC should most likely be positive. Today, B+ is about the only one of these terms in common usage.
I say classes instead of sizes - you could buy a B battery in a variety of voltage and current ratings. The first piece of gear I ever disassembled was a portable, all-tube AM radio (about 8"x6"x2", and it weighed several pounds). It had a steel chassis with 1.5V filament tubes, and three batteries. The B cell was about the size of a model airplane starter battery, but bigger than most you see, and IIRC, was 67.5 volts for the B+.
-Miles
If you have an amp with multiple channels (whether you can switch between them or not), this refers to running a (preferably short) cable from an extra input jack on the channel your instrument is plugged into to the input jack of an unused channel. This will often enhance the sound, so long as the channels are in phase with each other. Some amps (such as many fender reverb amps) have an extra stage or three in one channel (reverb, more gain). In this case, the sound will most likely be thinner, but you can always try; it won't hurt anything.
Well, it *is* being split at the jumper point but that's hardly the beginning. I haven't thought much about this, this is just off the top of my head.
So, there's at least part of the answer.
-Miles
Leaving it on all the time is just wasting power and yes, the life of the output tubes.
One thing to avoid is leaving the amp on standby for very long periods of time. This tends to poison the cathodes of today's tubes rather quickly.
Shut her down when you ain't playing. Your light bill will thank you.
No reason to rotate tubes, with one exception: If you are using an amp with 4 output tubes and it has a "half power" switch, OR you are pulling two of the four tubes for a half-power trick, then you might want to rotate the 4 output tubes only. Swap the inner and outer pairs once every couple of months or so.
If you don't want to bother with that, then don't worry about it.
-Larry (Dr. Nuketopia)
The standard is the Shure SM57. This has probably been used more to mic guitar amps than all other mics combines. You could try a Shure SM58 as well, but it has an extra peak in the vocal range some folks don't like (others do).
(various posts)
...the Sennheiser 421...
-Robert Cooney
Although there are certainly differences between mikes, as long as you have one that doesn't produce diaphragm distortion when exposed to high SPL it'll do a reasonably good job; the passband of a typical amp/speaker combination is seldom greater than 60-8000Hz, and most mikes are fairly flat within that range. That said, I like the 421 too.
-Lord Valve
I'd wipe it down with a little dish detergent mixed with warm water. Don't drown it, a little will do. Then while it's still wet, loosen up any stubborn dirt with a soft scrub brush, like they make for cleaning your knuckles. An old toothbrush is good for getting into tight corners. Wipe it down with a clean rinsed in clear water, then dry it off with a dry cloth. Repeat if necessary.
-Kent Pearson
Kent goes on to suggest a coat of ArmorAll[tm], "Don't use the high gloss stuff, use the low-lustre one. Avoid harsh chemicals, especially on the control panel." Others have warned that ArmorAll can destroy Tolex. Read the label and decide for yourself.
Ole Dantoft once told me how to do this and saved me having to read it in the manual:
You can check your firmware version by holding down the "MANUAL" knob while turning on the power, and it'll display "P O D X Y" one letter at a time, with "X" being major version and "Y" being minor
e.g.
X=1 and Y=4 for version 1.4.
-John King
It made a weird noise because you did weird stuff to it. Do you ordinarily whack your tubes while you are playing the guitar? I shudder to think how many perfectly good Mullards, Telefunkens, Bugle Boys, etc., have been canned by people who decided they were bad based on a bogus test like that. All tubes - all, without exception - will make noise if you smack 'em. It's normal. If a tube is too microphonic to use in a high-gain position (i.e., makes whistling, howling, or other feedback-type noises, or picks up undesireable cabinet vibrations) then it may well give years of trouble-free performance in a phase inverter, tremolo oscillator, or other lower-gain application.
-Lord Valve
You need a DPDT switch. Wire it as shown in the
diagram at http://aga.rru.com/FAQs/Images/par-ser-spkr.gif .
Make sure you get one capable of handling the current
you're likely to see in your speaker cab. I'd go with
at least a 5A switch. The overall rating is what matters,
not the switching rating. You should never be flipping
this switch while the speakers are being played through!
(inspired by a post from Chris Morbacher.)
The rectifier turns AC (alternating current) from the wall into DC (direct current, like a battery provides). Amp electronics need DC to work. Without rectifiers, you'd need batteries, and even a Champ would suddenly be a lot bigger and weigh a bunch more (and cost a lot more to operate). A Fender Twin or Marshall would be useful only to the very rich or the military.
-Miles
Assuming you mean the one at http://www.aopen.com/products/mb/ax4b-533tube.htm, yes. We've discussed it about 84 times, but thanks for checking.
Like everything else opinions vary. I don't know about the lurkers, of course, but most of the expressed opinions were that it would (a) probably not work that well and (b) most likely have heat problems. A google search will provide you with plenty of opinion fodder. I think most of us would vote, "or what".
-Miles
I've seen many people post asking about clean boost pedals only to be told "just use the guitar volume knob, dude" and many others ask about overdrive boxes and get told "just get an amp you can crank up, then control the overdrive from the guitar." Both valid points, however nobody ever mentions the extent to which they're somewhat mutually exclusive.
Because of the natural compression that goes hand in hand with overdrive it's hard to control the output volume of your guitar sound from anything that's upstream of the source of overdrive. Varying the volume from upstream varies the input level of the overdriven gain stage, which tends to affect the amount of overdrive much more than it affects the output volume. That's what makes it possible in the first place to affect overdrive by adjusting the guitar volume knob.
Let's look at a case where the signal chain is simply guitar -> amp.
If the amp is very clean (not overdriven, lots of headroom, like a Fender Twin Reverb on 4)) then adjusting the guitar output will result in corresponding changes in the amp volume. If you need to boost yourself for solos you set the amp as loud as you'll ever need it and control the volume with the guitar volume knob and how hard you play it. This works well as long as overdrive isn't necessarily a big part of your sound.
If the amp is overdriven (like a Fender Champ on 10) much of the range of the guitar volume knob will have as much or more affect on how overdriven the amp is than how loud it is. If you get a fairly overdriven sound, and need to adjust the actual volume of the guitar in the band mix (e.g., to boost solos) then you'll probably need to do it downstream of the amp, e.g., put a mic on it and have a soundman adjust it in the PA. This is fine as long as you can depend on having a soundman who will adjust you as necessary all night.
If you have an amp powered in between the Champ and the Twin Reverb (e.g., Vibrolux on 6) then you'll get some overdrive out of it, and the guitar volume knob will affect amount of overdrive and output volume together at the same time. This kind of situation works well as long as the amp is as clean as you want it when you have it turned up as loud as you need, and as overdriven as you want it when you turn it down as quiet as you need.
If you can come up with a system like any of the above, great, you'll have the shortest, simplest, and arguably best-sounding path between guitar and amp and you'll have less gear to carry than a lot of folks.
In all three of the above situations you have no independent control over volume and overdrive from the guitar. They're linked together. With the Champ you get a lot of control over overdrive and less control over volume. With the Twin you get control over volume but not over overdrive. With the Vibrolux you get a combination. But in all cases they're linked together. What if you want to be able to control overdrive independently of volume? To do this most people get an overdrive pedal. With the pedal you can set the amp for as loud as you want it, turn the pedal on and dial in the amount of overdrive you want, then set the pedal output so that the amp is about the same volume with the pedal on or off. Now you can have overdriven and clean sounds out of the same amp at the same volume.
What about volume control in the above situation? If you've got the pedal off you can still adjust volume from the guitar just the way you did before. If you've got the pedal turned on, the pedal acts like the amp did in the guitar -> amp scenarios above - depending on how much overdrive you have dialed in, the guitar volume knob will affect both volume and overdrive in varying degrees. This can work for you if you can set the pedal so that it's as clean as you want it and as loud as you need it to be when the guitar is all the way up, and still as overdriven as you want when you turn it down to the quietest level you need to be.
What if we want to be able to control the volume independently of the overdrive level? The way to do this is to adjust the volume from somewhere downstream of the source of the overdrive. You could adjust the output level knob on the overdrive box, or the volume knob on the amp. Neither of these is too convenient when you're using your hands to play guitar (unless you have one of those Neil Young devices that adjusts the amp's volume knob from a footpedal). With a channel switching amp you could switch to a louder channel with the same level of overdrive. (For that matter, if that channel switching amp allows you to set overdrive levels for both channels [i.e., there are separate preamp and master volume levels for both channels] then you don't even need the stompbox overdrive, as long as you like the overdrive sound of the amp.) If you don't have a "channel-switching" amp but you have multiple channels in the amp (like most larger vintage Fender amps) you could make it a channel-switching amp with an A/B box. Plug the guitar into the overdrive pedal, the output of the overdrive into the A/B box, plug box output A into one amp channel, plug box output B into the other amp channel set to sound pretty much the same as A only louder - et voila! You have two levels of volume, independent of the overdrive level you've dialed up on your stompbox.
Another way to solve this problem is to put a volume boost downstream of the overdrive box but before the amp. This might be in the form of a volume pedal with continuous control of volume, or a box with an on/off switch to act as a clean boost. Examples of the latter would include EQ pedals set to boost some or all frequencies, "clean boost" pedals (e.g., the MXR "Micro Amp" and Electro Harmonix "LPB-2"), or other pedals that let you turn down the effect and increase the output with an output control (e.g., a Tube Screamer with the gain turned down and the output turned up). The Fulltone Fat Boost is another pedal people recommend for this. It's sometimes called a clean boost pedal but because it's got a gain control and some built in overdrive I'm disinclined to lump it with the Micro Amp and LPB-2.
My personal situation is that I've played in various bands where I wanted an overdriven sound most of the time, and needed to be able to boost my signal for solos, and often needed boosted solos to be *much* louder than my non-solo volume due to playing in large and/or very dynamic bands. [Aside: I think that when you play in large bands you have to boost much more for solos than you do in smaller bands because there's so much more going on; in a power trio you need less of a boost because there's not much masking the sound of the single guitar. I play in bands that range from 6-12 pieces.] I don't like to rely on the soundman to do all the boosting because 1) sometimes there is no soundman, 2) sometimes he's busy tweaking things besides solo levels, 3) often he doesn't know who's soloing until the solo is half over and 4) sometimes soundguys like to just set levels and disappear. With as large a boost as I need I find that adjusting volume completely from the guitar results in not enough boost or a very anemic sound when turned down for rhythm work. Because I plug two instruments into my amp I can't do the A/B box switching trick.
So I've evolved this system for myself:
Twin Reverb, modded for half power switch, set in half power mode. The amp is also modded so both channels go through the tremolo.
Danelectro baritone guitar into "Normal" channel turned up to ten. Since I play the baritone totally clean I have no problem controlling volume with hands and knobs.
I usually use a Barber Electronics Tone Pump II (TP) for overdrive. The TP has one on/off switch and a second switch for pre-set amount of gain boost (not enough that I can use it as a lead boost).
With single coil guitars (usually Tele) TP gain is usually set at about 9 o'clock, tone and volume around 12 o'clock. With humbucking guitars (usually SG or LP) I set the TP the same except that the gain is down to 7-8 o'clock. The TP stays on most of the time. If I want cleaner I might turn it off or back off the guitar volume.
TP goes into Micro Amp set at 12 o'clock. This usually seems to be about the right amount of boost for me. Sometimes if I've got the tremolo on I'll boost the guitar a little with the TP pre-set boost or by cranking the Micro amp to 2 o'clock-ish because the tremolo reduces the overall volume level.
Micro Amp goes to a delay pedal and to the Twin set on 5 or so.
Twin Master Volume is set between 5 and 10 depending on the room and how loud the other 5-11 members of the ensemble are playing.
-Scott McKnight
Normally in a tube amp, you are dealing with a positive voltage (B+) with reference to ground. But with a bias supply, you are dealing with a negative (C-) reference to ground. Ground is just a handy reference when it comes to voltages - remember that you can have AC ground, signal ground, and PS ground - and they're all usually the same ground!
-Miles
A, B and C once refered to battery classes for circuits. (You'll notice that tube texts generally show batteries as power sources for the various circuit coltages - they meant it!) You had A batteries for the heaters, B batteries for the plate voltages, and C batteries for bia supplies. I say classes instead of sizes - you could buy a B battery in a variety of voltage and current ratings. The first piece of gear I ever disassembled was a portable, all-tube AM radio (about 8"x6"x2", and it weighed several pounds). It had a steel chassis with 1.5V filament tubes, and three batteries. The B cell was about the size of a model airplane starter battery, but bigger than most you see, and IIRC, was 67.5 volts for the B+.
That radio, BTW, was a marvel of packaging. Considering the size of the components, it had a far greater component density than just about any non-digital stompbox you're ever seen. Things were downright cozy in there. I can still feel and smell the caps, the resistors. I took it apart with a woodburning tool at 13. There was magic in that package, and I just had to learn that magic!
-Miles
It's on the ground lug with the yellow/red and the green. Couldn't be bias tap, there would have been smoke by now. My guess is electrostatic shield.
-Mike Schway
There's lots of info available at http://www.capacitors.com/pickcap/pickcap.htm. (courtesy Dave, AKA dwavetone)
Go to this site http://members.tripod.com/~roymal/accutron.htm . This will explain the archaic and arcane language of the reverberati. For all secrets are revealed in the model number, but only for ye who have wit to comprehend.
-Ronsonic
Go to http://groups.google.com/ . Select "Advanced search". Enter "Cyber-Twin" (or whatever) in the keyword box, and "alt.guitar.amps" in the newsgroup box. Search. If you can wade through all the flames and rhetoric, you'll find the group's opinions in lurid color.
-Miles
Check out http://www.retrovox.com.au/amv137.html. (courtesy Doug Roccaforte)
Harmonics are a by-product of distortion. Even when an amp sounds clean, there is generally some distortion present, and the nature of that distortion may produce predominately even, predominately odd, or similar amounts of both even and odd harmonic distortion.
The terms "even" and "odd" are very basic. Harmonic distortion is produced in multiples of the fundamental frequency. If the multiple is even, (2, 4, 6, etc.,) the harmonic distortion is even order. Likewise, if the multiple is odd, (3, 5, 7, etc.,) the harmonic distortion is odd order.
For example:
Lets say you play an open "A". The fundamental frequency is 110Hz. This is the open A string on a guitar. If your amp is producing predominately even order distortion, then the harmonics will be even multiples of 110Hz. The 2nd harmonic will be 110*2 or 220Hz, the 4th will 110*4 or 440Hz, and so on. Isn't that nice? 220Hz is also an "A", one octave above the fundamental, and 440Hz is "A", two octaves above the fundamental. The 6th will be 660Hz, which is a slightly sharp "E", (the 12th fret of the 1st string is 659.255Hz.)
As it turns out, except when distortion is severe, the amount of harmonic content, or the amplitude, diminishes as the order of the harmonic increases. Because of this, the out of tune 6th harmonic is not of any great consequence.
So, even order harmonic distortion is considered more "musical," as the 2nd and 4th harmonics are just octaves of the fundamental.
Odd order, on the other hand, is clearly not musical. The 3rd is 330Hz, which is a slightly sharp "E", the 5th is 550Hz, a quite flat C#, and so on. But this is what rock and roll is all about! Disonant energy!! An amp producing predominately 3rd harmonic distortion is nearly like playing in parallel fifths! A serious no no in real music, but done all the time in rock.
And nearly all of the great rock and roll guitar amps produce predominately odd order harmonic distortion. The trick is to design an amp that produces the odds and evens in a magical proportion...
-Gary Gerhart
Caveat: I would say that odd order harmonics are not necessarily "unmusical" if the overtones are mixed with the fundamental in moderate amounts. Certainly not to nitpick Gary's reply, which was very informative -- many guitarists prefer the sound of predominantly even order harmonics, and Gary writes from that perspective.
But stepping outside the guitar world for a moment, a clarinet, particularly in its lower register, produces an overtone series that contains prodominantly odd-order harmonics. Odd-order harmonics, mixed in proportion to the fundamental tone, tend to produce a sound approximating a square wave -- that typical reedy sound (compare a clarinet sample with a pure square wave on a synth, if you have one). Of course, no real world instrument produces a true square wave, but a clarinet is a good example of a predominantly odd-order, "square-wavish" sound. Certainly not "unmusical," although it's also certainly not a sound that many guitarists are going for!
Mixed OUT of proportion, as Gary states, odd-order harmonics can become harsh and unpleasant (to my ears) very quickly....
Gary's final point is also well taken -- the magic (especially for guitarists) happens with the right mix of even and odd order harmonics. To take another example, a violin, cello, or other bowed, stringed instrument has a very complex mix of even and odd order harmonics, and if Gary or any other amp manufacturer can ever nail that tone, sign me up!!
-TB
Yes, but the standard product will make it shiny and slippery. According to David Axt, there's also a Satin version. Claude recommends Meguiars Rubber&Vinyl conditioner. #40 (silicone free). Rich K recommends Vinylex DH-60 UV Screen. One brave soul braved the flames to recommend WD-40 (I wouldn't. -Miles) John Shinal has used Kiwi shoe polish. Most people just use soap and water. As Doug Roccaforte pointed out, some of the products mentioned will attract dust.
In my experiences, I've seen Mullard EL34s handle themselves just as good as a 6CA7. The 6CA7 is an american tube. We never made EL34s(Europe did), but our tube is very close in bias and a few other parameters. Personally, I prefer EL34s over 6CA7s.
They do operate differently.
Because our 6CA7 has "beam forming plates", its a more effecient design, also having a better, or stronger bass response.
The distortion is different from a EL34, I like the EL34's midrange distortion better. All beam power tubes have a certain round glassiness, pentodes seem to have better compression and midrange. At least to my ears. For players who want less compression and more headroom, the 6CA7 is certainly an upgrade over EL34s.
Real EL34s have a straight bottle, real 6CA7s are more "bulb" shaped, somewhere between a 6550 and 6L6GC in looks.
-Doug Roccaforte
For the non-tech, what it usually means is someone in marketing wrote the ad-copy you're reading. It's a technical term describing a mode of amplifier operation. The term sounds "more betterer" than "class b" or "class c".
Since marketing people are always looking for words that sound "more betterer" they stole the words.
Usually this happens when a marketing guy, who are usually banned from engineering meetings, shows up with donuts at the door of the meeting room. Engineers, although smart people, are usually hungry for donuts and let the marketing guy into their meeting against their better judgement.
Out of an hour of chomping donuts and talking tech, this is what the marketing hears:
"blah-blah-blah-blah-blah-blah. Blah-blah-blah-blah. Blah blah, blah and blah, 50 watts. Blah blah blah, blah blah, blah, blah blah blah. Class A blah blah blah blah blah blah blah blah. Double sided, plated through hole, blah blah blah blah blah blah blah blah. Blah, blah blah blah blah blah blah welded chassis corners. Blah blah blah blah blah blah blah blah blah blah blah blah blah blah."
So when the product comes out, the adverts all say, "50 watts of Class A power, high-strength welded chassis, solder joints made on both sides and through the board!"
The engineers look at each other, shake their heads and say, "Well at least he brought donuts."
So what class A means to you, the player, is there's a donut shop near the amp factory.
-Dr. Nuketopia
(For a technical explanation of Class A, AB, etc, refer to the class descriptions in the Technical FAQ.)
(First, make sure you have a properly wired three-wire power cord with a three prong connector. Check out http://www.rru.com/~mro/Guitar/Amps/Kalamazoo/Mods/safe.html for details, or see a tech. -ed)
Get a cheap neon tester. Keep it in your giggin' kit. Touch one probe tip to your finger and the other probe to the suspect chassis (or mic, etc). If it glows even a little bit, you have a problem. At the outlet, one probe to the small slot (120V) and the other to the round or "D" shaped (ground) slot or cover screw should light the neon. If the wide slot (neutral) to ground makes it glow, use a different receptacle!!
$2.00 can save your life (or make it less painful at least!!). The last time I was at Radio Shack I noticed they had plug-in receptacle testers for $6, I think.
(The above assumes you live in the USA)
It very well *could* have been a miswired outlet at the venue that was the cause of your shock, audioarc. Or it could have been your screen name... :o)
-Dave
Licensed Electrician
Robert of QTS says:
Tough one. I'll throw out some 'factoids':
Jim Anable added:
When I buy NOS, I don't care about packaging. What I want is a good tube that tests new or better. Many sellers say "tests new," that's what I'm looking for. Now, I happen to own a half way decent tester, and I'll tell you that they don't always test out.
Having said that, brand new tubes often do not test at recognized nominal new values, either! I have "tested used" and "NOS" tubes that test stronger than new Chinese and Russian offerings.
Ron Sonic added:
Buy from a reputable source.
One thing to look for, on many octal types, near the base, you can see the leads running through a tall ridge of glass. Prolonged heating changes the color of those leads progressively from (usually) red to black. Usually takes a couple hundred hours, usually. This is a completely inexact science. It can tell you new from used, usually.
Ron also noted that ``...most tubes are lettered with a chalky white ink that falls off the moment it gets damp or handled much. Even back in the day the unscrupulous would collect pulls wash them and rebox them and sell them as new. Logo's that wash off make that much less profitable.''
Doug Roccaforte had the simplest answer: Turn up the volume.
This sometimes works with dust, but seldom with grime (maybe with HiWatts), so let's go a bit further. RonSonic said: Paint brushes are underappreciated as a cleaning tool. Spraying a bit of 409 or windex or some such on the brush will help. You don't want to get the cone wet but a dampened brush isn't going to hurt it either. A slightly damper brush and a paper towel will do fine on the aluminum dust cap.
PMG noted: Those aluminum dust caps are really easy to dent, so use a lot of caution. They'll still work ok if you dent them but they'll be uglier (and went on to recommend a dry ratg -ed).
Doug Schultz got more hard core: ... I used an air compressor and a blower nozzle to clean out the folds in the surround. Be careful though, you can blow right through the paper. Other than that if you are careful with a damp paint brush you can get the dirt off without hurting the paper. It is very easy to damage these speakers with cleaning but a paint brush (even dry) and an air compressor worked very well to clean off the bar grime for me.