Re - caping an Ampeg vt22 or v4.

These amps have 550 volts dc and that can

This is NOT a beginners amp project!
OK lets take a look at the original circuit. There are 4 multi-can caps used, 3 triple metal cans and 1 double cardboard can. 2 of the cans are identical, and contain a 70uf and two 40uf units. In each of these, the 70uf and one 40uf are paralled together to make a 110uf. These are then connected in series to create a 55uf at very high voltage. The remaining 40uf section in one is not used, the other is connected in series with the cardboard can for the screen supply...

The cardboard can has two 20uf units, and they are paralleled to make a 40uf. This, in series with the previously mentioned 40uf, make a 20uf at high voltage.

The last triple can is used as 3 independants. Each one is 40uf.
Now this is one of the most complex power supplies you'll ever find in a guitar amp! Re-doing it presents quite a challenge for some people!

I decided to replace the impossible to find "triple" cans with easily found single replacements. All of the cans I used are singles except for one which is a dual 50uf. These are still easy to find, but you can use two separates here as well if you want...

The first cap, which was made up of parts from the triples, is now made from two units, each 100uf at 450 volts, connected in series. You could even use 400 volt caps for this. Remember that one of the series caps cannot be connected to ground, nor allowed to touch ground. The original amp's caps were in isolated mounts. You must isolate the new caps somehow as well. I suggest you wrap them in black tape and mount them with plastic tie wraps.

The new screen supply is made from two 40uf 450 volt caps, wired in series. Again, isolate at least the upper cap.

The last triple cap can be replaced with 2 or even 3 caps, depending on if you get a double. You can use 40uf or 50uf caps for these, at 450 volts. Remember to use the same ground wires that were on the old cans, don't change anything except you can make a wire shorter if that fits.

Check out the photos on my Ampeg pages for hints on doing this job, oe Email me if you have questions!
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You know, I've heard about some companies selling 'kits' of capacitors, but some of the parts can't be used, because they are all multi-cans of such values you would have to series connect the 2 caps in one can - quite an impossibility!

So check what you order very carefully, and make sure the parts can be used.

Another thing, if you want to order caps from a supply house, make sure they are rated for high ripple current, POWER SUPPLY duty, not just general purpose caps, else they will either blow up, or fail a bit pre-maturely...
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