Gibson Ga-15rvt - what is this capacitor?

[Danoblaster]

Hey all-I need some help. Got this Gibson and I want to change out filter caps and replace cord. I noticed this cap that appears to be a modification. Should I remove it, what was it intended to do? I have basic soldering skils...now how to discharge caps and have a dim bulb tester, and a DMM, but a novice. See any thing else that I should replace or is an issue on this amp? Thanks for any input or suggestions!

[The Dude]

That newer looking cap looks to be in parallel with one of those multi-section caps. I'd bet the original cap is/was bad and someone tacked in a new/parallel cap as a repair.

[Danoblaster]

Thank you ok, I will take out that cap and replace the (2) 20uf 450v filter with 2 sprague atom 20uf 500v and the (2) 20uf 350v with the same values..should I replace some of the smaller caps too?

[Enzo]

Agree^^^

Resist the temptation to look at anything you don't know as something to be removed or otherwise is "wrong".

[Enzo]

The two brown ones held on by straps really should be removed and replaced with something. Is ther any reason to think the blue one is defective? it is already a replacement for half of one brown cap.

The bright orange "Orange drop" caps are already recent era caps and are unlikely to be bad. The other darker brown ones may or may not be leaky - determine that with a volt meter.

I'd probably replace the small black 2mfd (2uf) electrolytics. I see three.

[Danoblaster]

I agree with that philosophy but I have looked at other Ga-15rvt amps and that cap is not there so i think the Dude is correct

[Enzo]

You can see in the picture it is wired to one of the red wires from a brown 2-section cap. Once you replace a bunch of caps, you can look at other amps and those won't be in it either. Unless it i sbad, removing the blue cap is just undoing part of what you set out to do.

[Danoblaster]

Yes I could reuse that cap when removing the the brown filters...will replace smaller 2uf and test brown caps. Thank you for the suggestions and input!

[drewl]

Those orange coupling caps are stock for these amps.

[Leo_Gnardo]

Thank you ok, I will take out that cap and replace the (2) 20uf 450v filter with 2 sprague atom 20uf 500v and the (2) 20uf 350v with the same values..should I replace some of the smaller caps too?

Unless there's some particular reason you want to spend all the extra money, skip the Atoms and use any competent electrolytic caps. One example, F&T work fine at a fraction of the price. Although I'd recommend avoiding F&T two-in-one caps. They may seem convenient but I find the leads are fragile and tend to break off, a bummer we can do without.

Time was, say 1960-2000, Sprague Atoms were top of the pops. I got over them about 15 years ago when it was revealed Atoms were mostly stuffed with fluff plus a much smaller modern-version cap inside. "Why they do that?" you may well ask. To reap extra $$$ from those who still fervently believe Atoms are all that and a bag of chips, which they most assuredly are not.



^^^ stuffing removed so you can see the business end clearly. FWIW stuffing looks like dacron/polyester fiberfill commonly found in pillows.

Sometimes Spray-goo cheats on the specs. Or, who knows, caps can be counterfeited too. Anything to make a buck.



Thanks to our friendly neighbors at The Amp Garage for bringing this to light.

[SoulFetish]

These Nashville caps should go too. The age horribly, and I've seen so many go bad, I don't even bother testing them anymore. I replace them as a matter of service.

[Mick Bailey]

I'm usually suspicious of paralleled PSU caps. There's a trend for 'stiffening' the power supply with many amps by increasing one or more filter caps by either replacement, or by installing a cap in parallel with an existing one - sometimes to the detriment of the original design. It's worth investigating if it's a mod or repair. Either way, the Stick-O-Dynamite caps are candidates for replacement by now and I would replace all the old electrolytics if you're servicing the amp. Often there's enough space to install can-type caps with solder terminals inside the chassis (such as JJ etc). I make up brackets out of aluminium sheet with a piece of shrink wrap as a cushion to firmly hold the can, and shrink wrap the terminals to give added insulation.

[Danoblaster]

Great information! Wow really surprised on sprague caps...what a bunch of bs. Thanks for insight and will get to work on all the electrolytics. Great forum!

[The Dude]

I'll add: There's no reason you couldn't use radial caps in this instance. It would be just as easy or easier to mount them and you can probably find them good quality at a lower price.

[Leo_Gnardo]

I'm usually suspicious of paralleled PSU caps.

Yes, when I see tacked-in "helper" caps I reckon somebody's been fiddle faddling with the fix. Enough of that, it's high time to rip 'em all out and do it right.

SoulFetish, good call on swapping out those "Nashville" caps too. They're also on my "immedate replacement" list. Along with Hunt's caps often found in old UK gear, you can pretty well count on them being kaput.

Leaky interstage DC blocking caps another headache on these gems.

Don't look now, but the old resistors in these amps are usually drifted well out of tolerance too.

Did anyone mention, grounded AC cable? Yes, do that too, & dispense with the death cap if those haven't yet been done.

Always a pile of work, but well worth it once all's done right. The old Gibson (and Epiphone & similar) amps I used to dismiss as sounding "thin and horrible" can actually sound surprisingly good when properly rebuilt.