1964 Fender Vibroverb

[futureblues]

Recently acquired a fender '64 vibroverb that looks mostly original to my untrained eye. I think a new baffle was put in after the d130f was reconed. The guts look mostly original too besides the bias caps and i'm not sure about the term LDR - didn't expect to see it on top the board.

The filter caps also look original and have some small but noticeable leakage on the ends.

It plays fairly nicely, but i think it needs a little love because i've heard a noticeable volume drop when playing. Any suggestions on where to start troubleshooting ?

Any other suggestions on how to get this guy back close to original would be great as well (bias, ldr/trem, any anything else i might have missed)

Thanks for any suggestions!

[Tom Phillips]

Looks all originl to me too except for filter cap replacement in the bias supply. Keep those clue tubular caps in the amp. They hardy ever go bad. If you can get better photos please post them.

[Chuck H]

A sweet and desireable amp, as any SRV fan will tell you. Odds are good that if the bias caps were replaced then the filter caps were replaced. If you lift the "dog house" you can take a pic of the filter caps and see if they're original or replaced.

Volume going up and down is most likely a tube problem. But regular service, including checking old resistors for drift, checking tubes, checking voltages, filter caps, bias conditions and cleaning pots and jacks is always in order when you get an old amp. This service will usually reveal if there are any other issues.

[futureblues]

Finally had some time to break the amp open again and take a few more pictures. The filter caps appear original and look to be in need of replacement.

3 of the caps underneith are marked 20mf 525wvdc/550vsp (Astron)
The other 2 are 70 mfd, 350 VDC (Mallory)

After looking a few online retailers for sprague atoms (thetubestore, mojotone) it doesn't look like they carry 525/550V caps. Is 500V sufficient ? Any other online retailers i should look at ?

I'd also be interested if anyone else has a 64 vibroverb how the internals compare.

[jmaf]

Wow, clear top 6L6's. Must sound like the heavens.

Those are 550 peak voltage for short pulses, they're 525 V rated. These are probably the current day incarnations: Sprague Atom 20µF / 600V

You can replace these two: http://music-electronics-forum.com/a...1-img_0835.jpg

With one of these: Sprague Atom 100µF / 100V

Just my 2 cents.

[Chuck H]

The 500V Atom caps will be fine. But change the first "parallel" filters to a pair of 100uf/350V caps in series (- of the first cap to + on the second cap at the junction) with 220k/1W resistors across the leads of each cap. Replace ALL the electrolytic caps in the amp. Even the ones that have already been replaced. And... As mentioned above, check resistors for drift, clean/re-tension all non fixed metal contact points like jacks and tube sockets and clean the pots.

[futureblues]

Thanks chuck / jmaf!

After some reasearch I'm going to pick up some deoxit to clean the pots, jacks, and tube sockets while I wait on parts.

Hopefully that'll give me enough time to understand complex impedance Is it standard practice to put resisters n parallel with the filter caps on old fender amps ?

Jmaf, I hope the 6l6s are still good given the occasional volume drop I experienced. I'd hate to have to replace them. Shouldn't the 2 bias caps that are in series be replaced with a single 50 uf cap ?

Thanks again

[Chuck H]

Is it standard practice to put resisters n parallel with the filter caps on old fender amps ?

Yes. It was done on a few amps that had series caps instead of parallel caps. The series arrangement increases voltage rating for the circuit but requires caps of roughly double the uf's.

And it hardly matters if it was stock or not. Because you can't get the stock parts to build the stock circuit. So your only option is to rebuild it as best you can with modern parts.

Shouldn't the 2 bias caps that are in series be replaced with a single 50 uf cap ?

Yup. Lose 'em. Replace ALL the electro's in the amp. If the bias supply is modded in any way, unmod it. The schematic and layout are redily available for your amp so this shouldn't be too hard to do.

Did I mention..? REPLACE ALL THE ELECTROLYTIC CAPACITORS IN THE AMP!

[jmaf]

Thanks chuck / jmaf!

After some reasearch I'm going to pick up some deoxit to clean the pots, jacks, and tube sockets while I wait on parts.

Hopefully that'll give me enough time to understand complex impedance Is it standard practice to put resisters n parallel with the filter caps on old fender amps ?

Jmaf, I hope the 6l6s are still good given the occasional volume drop I experienced. I'd hate to have to replace them. Shouldn't the 2 bias caps that are in series be replaced with a single 50 uf cap ?

Thanks again

^^^ What Chuck said

[futureblues]

Thanks again guys! I'll let you know how it goes.

[Tan Vox]

I have had `64 vibroverb more than 20 years now and and I have not altered it changing caps or fixing it. All I have done is keep fresh tubes there. Every time you alter your amp you ruin your amps vintage value. Fix only if you really must. I have more than 20 vintage amps, most in original condition. (I have rent my amps for band like BB king, Dylan, Peter Green, John Mayal.) You must remember you have a really beautiful vintage amp and it is the best without altering anyway. Try only new tubes - NOS 6L6 if you can find. Fix all 7025 and 12AT7 too. If your amp works fine after that, only enjoy!

[Chuck H]

You go girl.