Here's a bad cap

[nashvillebill]

Thank you.
That is about my opinion as well.
Too often, people see old amps and immediately think "recap?".
I think it's crazy how some people claim to hear a difference between tone caps in an instrument but don't think changing ten or fifteen caps in an amp is going to have any noticeable effect on the tone.

We can measure ripple in the power supply, and see if B+ is still holding up, that can give an idea. If it's not being gigged with, but still being played every few days, perhaps recapping wouldn't be a priority. But if the amp is going to sit for a few weeks or months in between uses, those old caps won't like that one bit.

Bottom line, though is that those caps were originally intended to have a lifespan of ten years or so, not 55. I would advocate recapping anything older than 1960 as a matter of principle. And don't forget those old Bumblebee coupling caps, or their equivalents. Of course, I deal with antique radios too, and it's pretty much automatic to change out caps on those. Those old wax-impregnated paper caps...ugh.

 

[JimmyM]

A few years ago, I had the original caps on my 73 Super Reverb replaced, and they looked just like that. My tech told me I was lucky it operated as long as it did.

 

[Dan Bass]

How old is too old?

When your dead, that's it.

 

[Bassmec]

How hot the amp gets in way of an electrolytic capacitor can have a great effect on the life of the capacitor.
They come in two ratings 85 Deg centigrade and 105 Deg centigrade these days.
PS There are relatively sensible sized metalizesd film caps than can be used in tube power supplies. I have them in my RCA OP-6 Pre amp.
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[Mark Reccord]

How hot the amp gets in way of an electrolytic capacitor can have a great effect on the life of the capacitor.
They come in two ratings 85 Deg centigrade and 105 Deg centigrade these days.
PS There are relatively sensible sized metalizesd film caps than can be used in tube power supplies. I have them in my RCA OP-6 Pre amp.
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For the low low price of $97 for 200uF.
I'll stick with electrolytics for filter caps at that price.

 

[Bassmec]

For the low low price of $97 for 200uF.
I'll stick with electrolytics for filter caps at that price.

I agree for my Bass Amps I like the Mlytic 200uf 200uf dual cans.

+ if you are going to give an old faithful amp a birthday!, a bit of extra quality won't hurt.

 

[MYLOWFREQ]

How old is too old?

I'd say 12 to 30 years in general. I fixed an MXR distorion II that had a bad cap, and it was made before '85. No surprise there however, I also fixed an EH memory toy that also had a bad electrolytic cap and it was a few years old, so who knows..

 

[agedhorse]

I toured with power amps that were 20 years old with zero cap failures and the amps still met spec.

I still use some rack mount mixers that are 25 years old (like 12 of them) and no cep problems here either.

It really depends.

 

[Downunderwonder]

Oh well, I guess that's good reason to leave it alone. The preamp valve puts a bit of heat into the EQ section and the fan pushes warm air out of the front from the power amp. It never gets ''hot''.

 

[middy]

It would be nice if caps were installed in easily swappable holders like fuses.
Job security for techs, I guess.

 

[B-string]

It would be nice if caps were installed in easily swappable holders like fuses.
Job security for techs, I guess.

No that would be functionally a disaster! The problems that would cause are staggering.

 

[middy]

No that would be functionally a disaster! The problems that would cause are staggering.

You're the expert, I'm not going to argue, just ask for further elaboration.

 

[Mr. Foxen]

It would be nice if caps were installed in easily swappable holders like fuses.
Job security for techs, I guess.

Consider how often amp issues are resolved by reseating the valves. Now imagine that reseating valves exposes the person doing it to 400v stored inside the valve via the pins that poke out of it.

 

[B-string]

You're the expert, I'm not going to argue, just ask for further elaboration.

Top of the list? Easily contacted dangerous voltages, voltage/current losses from mechanical only clamping, arcing and associated audio and RF noise from it, heat damage from the voltage/current losses. Entirely possible for a perfectly good cap to no longer function in circuit due to the mechanical only connection points. Ever try to replace fuse clip ends on a PC Board? Much more difficult than a wire leaded cap.

 

[middy]

I hadn't even considered the fact that they can shock the crap out of you... See? This is why I just play the things and let y'all fix them.

 

[Mr. Foxen]

Amps made to outlast the caps have the board caps soldered to turrets, and the cans in clamps to to make changing them a minor job though

 

[Relsom]

I'm going through this right now too. Got 250w Dukane paging amp from the 80's or 90's that pops the main fuse immediately. Found one of the two 6300uf 100v electrolytics is shorted. Absolutely no visible indication of a fault. Years ago I could probably find these caps for $15 or $20. Presently they're are in the $90 range. Too much to put in to an old amp that likely needs other components replaced as well before I would be comfortable putting it back in service. The thing ran non-stop for 20 years (school system) before crapping out.

 

[B-string]

I'm going through this right now too. Got 250w Dukane paging amp from the 80's or 90's that pops the main fuse immediately. Found one of the two 6300uf 100v electrolytics is shorted. Absolutely no visible indication of a fault. Years ago I could probably find these caps for $15 or $20. Presently they're are in the $90 range. Too much to put in to an old amp that likely needs other components replaced as well before I would be comfortable putting it back in service. The thing ran non-stop for 20 years (school system) before crapping out.

Just add another 500mfd (no big deal less than 9% over and caps are +/- 20%) and you have a $23 cap. Invalid Link Removed The 6300mfd was $101. More common use values really bring prices down.

 

[Relsom]

Thanks for the tip B-String. I may do deeper into this amp now and do just that. I've had good luck with Mouser before. Got a dozen tactile switches sent for less than what Roland charged for 1.

 

[B-string]

Mouser, Digikey and Newark are in my stable of favorite supply vendors. Have fun with the project!