Capacitors



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Zealots:


capacitors are our friends. In this issue I will explain what they are, what they do, and
finally how you can change your filter caps and make your amp have something most of us rarely
experience: Real BASS!
What do they look like? That's the question that I wish someone answered for me when I fist
became curious about this stuff. The most easily identifiable are the ones that look like little brown
plain M&Ms, but there are also lots of other kinds as well: some look like little cylinders with
obscure codes on them, the old Fender tone caps look like blue Good- N-Plenty's, others don't look
like candy at all.
One thing that they all have in common is that they all have two leads, and they are marked with
two codes: There is usually s voltage number on the cap, which designates the highest voltage the
cap can handle. You will also see another code that designates is the amount of capacitance they
are capable of, in fractions of farads, usually designated by units of 'mfd' or 'uF.' Even smaller
fractions of farads, or picofarads, are designated by the unit 'pf'. Farads are units of capacitance,
but don't worry about what this means now. Just remember that if you see any of these three
abbreviations on a part, it's got to be a cap.



1) Find them and do not touch them. Clue: they are way bigger than any of the circuit board

components, usually around the size of tubes. They are usually on the outside of the amp chassis
with the transformers, not on the inside with the circuit board. In Fenders, they are usually under
a pan in front of the tubes. In Marshalls, they are usually all combined into a big brownish-yellow
cardboard tube. This tube really contains a few of them all rolled up into one convenient package.

2) Do Not Touch Them! They Must First be Discharged! I can not stress this enough. I still
have a small blistering burn on my finger from the filter caps in a tiny Fender Champ. A bigger
amp can store enough voltage to stop your heart, unplugged. Here's how to discharge them:
Unplug the amp, turn it on, and if it has a standby switch, turn that on as well. Connect one end
of a jumper wire with alligator clips to pin 1 on any preamp tube, then connect the other end to
the chassis (ground), essentially shorting pin 1 to ground. Keep this connection hooked up while
you work inside the amp and allow a few minutes for any stored charge to bleed off before you
start work.

3) Unsolder the caps and remember how they are connected, find replacements, and
solder them in the same way. Use a pencil to remember where they go and what the polarities
are! It can be really tricky to try to interpret this from a schematic because the wires are all under
the fiberboard on a lot of amps. If you are replacing multi-caps, they might have six or more
leads, so be careful. Replacements are hard to find from electronic warehouses because there is
just not that much equipment out there anymore that requires large amounts of filtering. You will
have better luck with Mouser, Antique Electronics or any of those warehouse-type places if your
looking for smaller values, and of course the price will be right. But for bigger values and voltages
you need to find a vintage guitar supplier, like Recycled Sound. The best place to look is in
Vintage Guitar Magazine. Ignore all the stupid articles about this and that $12,000 Telecaster and
go straight to the ads. There are at least five or ten companies like Hoffman and Kendrick that sell
them. Expect to pay anywhere from $20- $50 to get what you need for bigger amps. Also, if you
have a good store in your area that repairs old amps, you can usually get filter caps there.