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In Reply to: RE: There are always solutions. posted by Ralph on December 22, 2020 at 13:01:47
Thanks for this advice. Actually a few years back I needed to have one of the amps re-tubed,
and Roger Modjeski checked out both amps fairly thoroughly. He said the caps are fine, and recommended against replacing them. I am certainly not able to do this myself, and I don't know any local technician any more I could trust with them.
Follow Ups:
Filter caps are the thing that limits the life of almost any electronic circuit that uses a power supply.
I can't speak for Roger's reasoning at the time so I'll put it this way:
Electrolytic capacitors have a sort of 'half life'. Depending on the application, usually after about 20-25 years, half of the filter caps installed are defective in some way. This idea falls apart after that, because by the time you hit 40 years its more than 75% of them have failed. Now if heat is involved, the caps fail sooner; this is why filter caps last a little longer in solid state equipment. The quality of the part makes a difference too, as well as the age of the part prior to installation.
I mention this last bit because Harvey Rosenburg told me that he was sourcing a lot of his filter capacitors from a surplus source for the NYAL amps. That source was (Bill) Godbout Electronics. These parts, if in your amps, were photoflash capacitors and not well suited for use in a tube amplifier (not good at ripple current), although they were very good at having a lot of capacitance for their size. Harvey also told me that he stripped the casing off of the part, since they were made in Japan (by Rubycon) and the Japanese didn't like to see Japanese parts in their amps at the time. By stripping the plastic case off, the parts looked American unless you looked closely. This part BTW is a 600uf 360WV capacitor, slightly over 1" in diameter and about 4" long. This is an unusual form factor and might be part of the reason Roger didn't want to mess with them.
Harvey also told me that the source dried up (I didn't tell him that I knew the person that bought out the remaining stock) so he had to find something else. The point here is that filter cap was used when it was installed. Its also possible that your amp does not have this part if it was made a bit later.
Roger was a great guy and very competent. But in his last years (and I don't know how long because he kept this under wraps) he was in pain dealing with cancer and this affected his mood and judgement.
So you might want to revisit this issue. Put another way- 'nice amp you got there- it'd be a real shame if something happened to it'... :)
I can also tell you that we used brand-new parts in our amps and any of our product made in the early 1990s is needing new filter caps at this point.
What's scary to me is that many of the Japanese companies that for a while made the best available high voltage electrolytics (Panasonic and Nichicon) have ceased or are in the process of cutting back their production. Since, I think, electrolytics go bad even faster if they are stored and never used, I don't know what to do about this eventual problem. Or maybe I'll go before my capacitors go.
If you have an amplifier or preamplifier that needs the axial lead form factor, you are almost out of luck already. Panasonic makes none, and Nichicon makes only a few. There are those German capacitors sold by Antique Audio, still.
Hmmm..... do you know if the NYAL OTL3 falls in this category. You folks are scaring me. I may indeed go before my amps do---I'm almost 75---but I still would want to save these gems for posterity.
I haven't been able to locate Bruce Moore.
Bruce is a regular character that hangs out at the Analog Room in San Jose.
Brian, the owner of the Analog Room, could likely put you in touch with him. Best bet is to just go down to the Analog Room on a Saturday afternoon, buy a few records, and ask around.
Thanks very much for the information about the Analog Room. Unfortunately, this is already too late:
http://www.theanalogroom.net
(They have closed, but a relative will reopen a store in Huntington Beach.)
I might try to follow up nonetheless.
I don't think the output coupling capacitors required by the Futterman type design need to be high-voltage types, so you are probably OK in that regard. But upstream from the output the NYAL amplifiers are just like any other tube amplifier, in that they operate at hundreds of volts. It's those voltage ratings, say, above 100V, that are becoming less and less available.
The output capacitors in a Futterman type amplifier (SEPP) need to have the same voltage rating as the power supply caps. In case one of the upper bank tubes shorts out, bias fails or something else goes wrong full supply voltage will get applied to the output capacitors.
Caps should be rated minimum 400V working voltage for safety.
It's been more than 25 years since I owned a Futterman type amplifier, so my memory of the circuit has faded. Good point.
Thanks for this additional input. If I knew a local technician, I would ask them to look again. Does anyone know of a reliable and competent place in the Bay Area?
I don't know what sort of capacitors my amps have. The main power supply capacitors are covered by a special metal case with DANGER HIGH VOLTAGE plastered over them. There are also some fairly large black capacitors with red ends eternal to this case but next to it. Finally there are some wonder caps, which were added later, but I think these are to replace and/or bypass the coupling capacitors.
I suppose I should take the covers off and clean everything at some point. It is dusty inside.
But the covers are a real nuisance to deal with, held on by a plethora of small machine screws.
I still have the original boxes, so I guess I could ship them somewhere if necessary----a terrifying prospect nonetheless.
Bruce Moore designed amps and is the 'M' of MFA years back. He's still doing amplifier work, including repair.
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