how to recap a solid state amp

[hachi kid]

hey guys. my guitarist has a Sunn Beta Lead he's letting me use in our band, but it seems to need a recapping. I have a couple of questions: how can you tell if an amp needs to be recapped? and where can I find out how to recap an amp?

[skychief]

Age, mainly. The best caps typically last 10 - 12 years and then they start to degrade and their characteristics ... change.

Also, if you see BULGING end caps, thats an easy clue they're going bad.

[Mr. Foxen]

Not really any difference to recapping amps between solid state and valve, just the cap values change. Its the construction method that changes it. Probably not ideal thing to be fiddling with if you need a guide, but aside from physical fit, it tends to be connecting two lugs, and being very sure they are the right way round, as explosions result from getting it wrong.

[seamonkey]

Originally Posted by hachi kid

hey guys. my guitarist has a Sunn Beta Lead he's letting me use in our band, but it seems to need a recapping. I have a couple of questions: how can you tell if an amp needs to be recapped? and where can I find out how to recap an amp?

"seems to need a recapping"
Why?

[B-string]

If you hear a constant 120Hz hum coming from the amp, get it re-capped ASAP.

[RickenBoogie]

Have it done by an experienced amp tech. It's a case of, "if you have to ask...", and without the necessary hands on experience, it's risky.

[nashvillebill]

And even if you don't hear a hum, old electrolytic caps no longer function well. Power supplies can get "saggy" resulting in soft bass response. If used as coupling caps, frequency response can be affected. This degradation can occur so slowly that it's not immediately obvious to the user.

That Beta Lead is proably pushing 30 years old if not older. Those caps are living on borrowed time.

For those who are not familiar with electrolytic caps: they depend on a wet electrolytic paste inside the cap. When the cap is manufactured, the insides are put inside a metal shell and the end sealed. But no seal is perfect, and over time the moisture inside the cap dries out. Once the cap goes dry, its internal resistance goes up and the caps performance goes down. The cap can heat up to the point where it starts to bulge or even vent catastrophically. When power supply caps dry out, a 120 Hz hum can be heard when the power supply's ripple exceeds the output transistors ripple rejection. But even before that, the power supply rails will suffer from reduced voltage.

[hachi kid]

I said it seems to need recapping because that's just what my guitarist said. I've only played on it once, but I was getting some terrible noise from it. not sure what was causing it since I never got a chance to properly look at it. how much do recap jobs usually cost?

[johnk_10]

i just use my ESR meter to determine if an amp needs recapping.

[MuthaFunk]

Originally Posted by hachi kid

I said it seems to need recapping because that's just what my guitarist said. I've only played on it once, but I was getting some terrible noise from it. not sure what was causing it since I never got a chance to properly look at it. how much do recap jobs usually cost?

Every job is different depending on the circuits. They usually all have at least 2 or sometimes 4 larger caps on the power supply that will cost the most money. From there it's all just a matter of how many and what sizes that will cost the money.

Originally Posted by johnk_10

i just use my ESR meter to determine if an amp needs recapping.

I didn't know about these. Thanks for the info.