DISCLAIMER: LORD VALVE (W. WHITTAKER DBA NBS ELECTRONICS) WILL TAKE NO RESPONSIBILITY FOR ANY INJURIES OR DAMAGE SUFFERED BY ANYONE AS A RESULT OF THE MISINTERPRETATION OR MISAPPLICATION OF THE INFORMATION CONTAINED IN THIS ARTICLE. PROPER HIGH- VOLTAGE SAFETY PROCEDURES AND PRECAUTIONS MUST BE PRACTICED AT ALL TIMES WHEN SERVICING VACUUM TUBE AMPLIFIERS!! IF YOU ARE NOT COMPLETELY FAMILIAR WITH THESE PRECAUTIONS, SEEK GUIDANCE FROM SOMEONE WHO IS!
Here\'s the right way to do it: First, take the chassis out of the wood cabinet. Sometimes this is really easy, and sometime\'s it\'s pretty hard. I had to work on a reissue Vibrolux Reverb that fell off a stage last week; on the reissue Fenders, they use a piece of aluminum foil that\'s glued to the underside of the amp\'s top board instead of the stapled-on piece of window screen (or a piece of sheet aluminum, in the later SF amps) for shielding the open side. BIG mistake...the adhesive on this aluminum foil is the type that never really dries out...sort of like honey. Under pressure from the upward force of the chassis, and subjected to heat from the tubes and trannies, this adhesive bleeds out from under the foil and literally glues the chassis into the cabinet. Not only that, the four lath strips that go up the sides of the box (for screwing the backs and the front baffle to) are so tall that only about 1/8" of clearance is provided between them and the chassis, making it impossible to break the adhesive\'s hold by pulling the chassis downward. Not even removing the speaker baffle helped. I finally had to take a rubber hammer and pound a thin-bladed putty knife between the chassis and the top board, all along the front and rear, which caused the aluminum foil to bunch up inside the amp...still stuck to the top board, of course. It was still rough going pulling the chassis out due to the clearance problem. I had to rip off all the foil, clean all the adhesive off the underside of the top board and the chassis edges, cut a piece of screen to the right size, and staple it in place with a staplegun. All this, mind you, because some damn bean counter decided he could save fifty cents by not using a piece of screen. I also had to take a chisel and chop about 3/16" off the top of each lath strip, to make re-installation of the chassis easier and to avoid disassembly problems in the future. BTW, if you need to do surgery on the wood inside your amp, you can re-black the wounded portions with some leather dye. The stuff I use came from Tandy; a quart of it has lasted me over a decade so far. An "acid brush" (obtainable in the welding supplies department from your favorite mega-hardware labrynth) is ideal for applying it with; it sinks right in, and you can\'t tell it from the stock black. (Whatever it was.)
Anyway...once you have the chassis out, you have to eyeball the pots and see if they are accessible. If they are, like in old Fenders and Marshalls, it\'s a piece of cake. You\'ll need two type of Caig Labs chemicals...D5S-6, and MCL100LS-2. Put about a half-second shot of the D5 (red formula) into the pot, and rotate it vigorously 10-20 times. Let it sit for a couple of minutes, and finish it off with two shots from the MCL (blue formula) can, again rotating the pot vigorously 10-20 times. The MCL100LS-2 can emits a 1/4-second timed burst when you push down the sprayhead, unlike the D5 can, which will spray as long as you hold the valve down. The red formula takes care of corrosion and other nasties on the metal contact surfaces, and dissolves other crud so that it can run out of the pot. The blue formula is good for the carbon track, and also replaces any lubricating grease the red stuff dissolved, making the pot feel nice and smooth again. HEADS-UP: Do NOT put the red stuff into your console faders. It\'s damn near impossible to make \'em feel right again after you put any cleaning solution which includes a solvent vehicle (like D5S-6) into them. There is a 100% formula (no solvent) for the red variety, called D100-2. Use that instead of the D5, and follow the above procedure. Also excellent on EQ sliders and rotary switches.
Here\'s the weenie: If you find that you\'re looking at the solder side of a PC board where the pots ought to be, you\'ll have to pull the PCB out to clean the pots. This type of construction is very common (reissue Fenders, Crates, etc.) these days, so if you have a newer amp it\'ll be a pain in the ass. You\'ll need to pull all the knobs off the pots, take all the bushing nuts off, maybe unplug some ribbon cables and remove some screws which go through the PCBs into chassis-mounted standoffs. If you have LEDs on the front panel, you\'ll need to be especially careful not to bend the leads for them out of place while you have the PCB out. You may also need to make yourself a "gozinta." A "gozinta" is a device which makes sure the doctor juice "gozinta" the pot, instead of all over the place. (Maybe in your eye, nose, or mouth, if you\'re not careful. Trust me, D-5 tastes like utter crap. ;-) Since the slot where the contacts enter the pot body will probably be sandwiched between the pot and the board where it\'s damn hard to spray into, you\'ll have to take the red plastic tube that sticks out of the spraycan and bend it. (I have a whole truckoad of these, bent to various angles, for reaching into specific amps and mixers.) This is easily done by heating the tube carfully with a lighter (or propane torch throttled way back) where you want to bend it. Once it\'s hot, you can push it against your workbench to bend it to the angle you need. If you screw up and collapse the tube or melt it too much, just snip the bad part off and start over. Use the same procedure I outlined above, and then re-install the PCB.
Be aware that there are circuit conditions which can cause a pot to become noisy; you won\'t be able to tell the difference unless you know your tech stuff. DC on the pot is the most common one. If you have a pot that\'s still scratchy after you\'ve treated it in the way I recommend, it\'s either a bad pot or you can suspect a circuit malfunction. 90% of the time, a scratchy pot just needs to be cleaned. 5% of the time the pot is defective, and 5% of the time something\'s gone south in the circuitry. That\'s a 9/1 crapshoot, with the odds in your favor. Go ahead and clean \'em. '; 1;