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previous: Phil I recently bought a 64 vibro champ,... -- 6/17/2000 2:35 AM

Re: Re-Cap

6/20/2000 10:40 PM
MBSetzer	Re: Re-Cap I would assume no caps need to be changed, except maybe the can, and I would test it to make sure since a replacement will be newer but not as good a cap. When the average wet electrolytic capacitor of yesterday is allowed to rest without high voltage being applied for many years in a row, it can degrade to the point where re-forming the electrolyte after applying high voltage again will not be able to approach the performance of a brand new modern cap. The electrolyte eventually will dry out with age anyway but that may require more decades if the cap is superior and the amp is played regularly. It does depend on the quality of the caps though . . . This is most likely and most serious with the filter caps in the can of Champs rather than any of the other Champ caps. That said, I bought my mint '65 VC in 1981, and have played it almost every year since, sometimes only a few hours yearly, and probably the only extended storage was about 3years without turning it on. It was so clean I suspect it had more idle years between 1965 & 1981 than it has had since. It still needs no service whatsoever, these were the original Vibrochamps and built better than even the same amps of later dates. Yours most likely has a Sprague small can cap with the orange & white label, these are highly superior. Mine from 1965 continues to outperform the Mallory cans that were original Fender parts on the later Champs in the '70's. I have not seen many Mallory cans older than about 1975 that are usable, and it seems to me this type of experience has been seen by so many techs that there is now almost a universal tendency to replace old filters since it is easier than fully testing them. People didn't bring small amps like Champs & Princetons to a pro tech unless there was really something major wrong, so the pros may have a more accurate picture of what goes bad than stays good. But don't replace all the caps in an amp, especially not a blackface Fender! Inside the chassis, there may be some rare white Mallory electrolytic plastic molded caps on the preamp bypasses. These are highly superior solid tantalum dry electrolytics that do not leak or degrade through time, mostly if anything they just drift to lower capacitance values which usually improve the tone compared to when the amp was first issued. I would never remove one of these unless it was proven bad or simply HAD to be replaced with a different value, then I would still never discard one. There is probably more likelihood that guitar tubes will once again be made in USA than there is caps like this with as much tantalum. For the bypass of the 6V6, there is a physically larger cap that is usually not electrolytic, it is a paper & film type. Other than the can of the '70's Champs, this would be the other one to consider for LIKELY replacement. It is a 25mf/25VDC like the electrolytic tantalums, but it is non-polarized and will handle the power tube better than the white ones of the same value. That is because it should have really been about a 50VDC cap if it is to handle the tube at full volume, but most Champs were not played maxed very much so this one is usually still good too. The blackface does not stress it as much as a silverface champ anyway. You wouldn't think it is very special, but it is surprising how difficult & expensive it is to find a better non-polarized/non-electrolytic film & foil or paper & foil replacement. Today's more common metallized film caps really are not as good as the originals unless the original is toast. This is the one cap that would be at risk from ordinary use, although mainly due to loud playing. If my only choice were to use an ordinary (or even the best available military or audiophile) aluminum electrolytic as the 6V6 bypass, I would instead just leave this one off altogether, the amp works just fine without it with reduced gain. The treble cap, usually a ceramic disk of 250pf can be replaced with a silver mica 250pf for a little clearer sound, but the original is not likely to have failed. The remaining caps for signal handling are most likely blue epoxy dipped high voltage film & foil. These are sometimes considered irreplaceable by Fender blackface enthusiasts who may not even know about the white tantalums (thinking those have aged as they replace with cheap aluminums). Other than complete failure there is little that can go wrong with them other than a drift in value with time. These are the ones that are commonly replaced with modern Orange Drop types with stock or modified values in case the old ones were leaking or drifted higher in capacitance. Any of these that drifted lower would likely improve your opinion of the amp with most guitars. The Orange Drop is considered very close in sound to the original. So there is no current accurate substitute for original caps other than the blue ones (and those rarely need it since they don't degrade with age), quite a catch-22, so that is why I test & preserve as much of the originals as long as they are functional. In the vibro section there are usually 3 ceramic disks, which like the second 12AX7, are only used in the oscillator for the vibrato. Your signal does not ever pass through these caps or the second tube. If the vibrato works good they are probably fine, but if needed they can be replaced with Orange Drops which will barely fit but as far as I know now, the orange epoxy will outlast the old coating of the ceramics which becomes more permeable to moisture every year. Hope this helps, it might be just me but I would seriously hesitate before I would make any changes to a working blackface Fender, and then only the minimum required for restoral. Mike

6/20/2000 10:40 PM

MBSetzer

Re: Re-Cap

I would assume no caps need to be changed, except maybe the can, and I would test it to make sure since a replacement will be newer but not as good a cap.

When the average wet electrolytic capacitor of yesterday is allowed to rest without high voltage being applied for many years in a row, it can degrade to the point where *re-forming* the electrolyte after applying high voltage again will not be able to approach the performance of a brand new modern cap. The electrolyte eventually will dry out with age anyway but that may require more decades if the cap is superior and the amp is played regularly. It does depend on the quality of the caps though . . .

This is most likely and most serious with the filter caps in the can of Champs rather than any of the other Champ caps.

That said, I bought my mint '65 VC in 1981, and have played it almost every year since, sometimes only a few hours yearly, and probably the only extended storage was about 3years without turning it on. It was so clean I suspect it had more idle years between 1965 & 1981 than it has had since. It still needs no service whatsoever, these were the original Vibrochamps and built better than even the same amps of later dates. Yours most likely has a Sprague small can cap with the orange & white label, these are highly superior. Mine from 1965 continues to outperform the Mallory cans that were original Fender parts on the later Champs in the '70's. I have not seen many Mallory cans older than about 1975 that are usable, and it seems to me this type of experience has been seen by so many techs that there is now almost a universal tendency to replace old filters since it is easier than fully testing them. People didn't bring small amps like Champs & Princetons to a pro tech unless there was really something major wrong, so the pros may have a more accurate picture of what goes bad than stays good.

But don't replace all the caps in an amp, especially not a blackface Fender!

Inside the chassis, there may be some rare white Mallory electrolytic plastic molded caps on the preamp bypasses. These are highly superior solid tantalum dry electrolytics that do not leak or degrade through time, mostly if anything they just drift to lower capacitance values which usually improve the tone compared to when the amp was first issued. I would never remove one of these unless it was proven bad or simply HAD to be replaced with a different value, then I would still never discard one. There is probably more likelihood that guitar tubes will once again be made in USA than there is caps like this with as much tantalum.

For the bypass of the 6V6, there is a physically larger cap that is usually not electrolytic, it is a paper & film type. Other than the can of the '70's Champs, this would be the other one to consider for LIKELY replacement. It is a 25mf/25VDC like the electrolytic tantalums, but it is non-polarized and will handle the power tube better than the white ones of the same value. That is because it should have really been about a 50VDC cap if it is to handle the tube at full volume, but most Champs were not played maxed very much so this one is usually still good too. The blackface does not stress it as much as a silverface champ anyway. You wouldn't think it is very special, but it is surprising how difficult & expensive it is to find a better non-polarized/non-electrolytic film & foil or paper & foil replacement. Today's more common metallized film caps really are not as good as the originals unless the original is toast. This is the one cap that would be at risk from ordinary use, although mainly due to loud playing. If my only choice were to use an ordinary (or even the best available military or audiophile) aluminum electrolytic as the 6V6 bypass, I would instead just leave this one off altogether, the amp works just fine without it with reduced gain.

The treble cap, usually a ceramic disk of 250pf can be replaced with a silver mica 250pf for a little clearer sound, but the original is not likely to have failed.

The remaining caps for signal handling are most likely blue epoxy dipped high voltage film & foil. These are sometimes considered irreplaceable by Fender blackface enthusiasts who may not even know about the white tantalums (thinking those have aged as they replace with cheap aluminums). Other than complete failure there is little that can go wrong with them other than a drift in value with time. These are the ones that are commonly replaced with modern Orange Drop types with stock or modified values in case the old ones were leaking or drifted higher in capacitance. Any of these that drifted lower would likely improve your opinion of the amp with most guitars. The Orange Drop is considered very close in sound to the original. So there is no current accurate substitute for original caps other than the blue ones (and those rarely need it since they don't degrade with age), quite a catch-22, so that is why I test & preserve as much of the originals as long as they are functional.

In the vibro section there are usually 3 ceramic disks, which like the second 12AX7, are only used in the oscillator for the vibrato. Your signal does not ever pass through these caps or the second tube. If the vibrato works good they are probably fine, but if needed they can be replaced with Orange Drops which will barely fit but as far as I know now, the orange epoxy will outlast the old coating of the ceramics which becomes more permeable to moisture every year.

Hope this helps, it might be just me but I would seriously hesitate before I would make any changes to a working blackface Fender, and then only the minimum required for restoral.

Mike

Replies:

Rick Erickson q{Inside the chassis, there may be ... -- 6/20/2000 11:15 PM