Polyester film capacitors

Ray Gianelli

Ray Gianelli

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I'm going through a Marantz 2325 for a friend, following @Leestereo 's excellent upgrade thread. One of the things he does is to increase the stock capacitor in the output amplifier's high pass filter to a 1.5µF polypropylene film cap (the original is a 1µF polyester film).

When i do a restoration I don't bother checking the capacitors I pull out unless they look suspect, or I'll just spot check them to see if there's a trend. So when I pulled these polyester caps I just checked them for grins. i didn't expect them to be bad. But while one tested OK, the other didn't:
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I thought film caps didn't go south with age, but this one sure did. IIRC @blhagstrom pulls these out of Accuphase gear on sight and replaces them. I'm certainly going to be wary of them going forward.
 
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Those flat gray caps are known to be bad caps. I've run into the same thing with a couple model 140 power amps. Even if they are still within spec, they effect the sound, and not in a good way. Just replace them with a polypropylene film cap. In one of the 140's I replaced them with poly caps since one was out of spec. They were still within spec in the other 140. After restoring both with the same components, I did an A/B test between them. The amp with the polyester caps sounded kind of sterile compared to the other. I just replace those flat grays now when I run across them.
 
It's a rare event, but I have come across a few bad vintage polyester film capacitors. The last one was a 0.1uF green "chicklet" capacitor in the output zobel of an integrated amp.
 
Ray Gianelli said:
I didn't know that. Must have been absent the day you guys discussed it. :jump:
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It's been discussed in the Marantz forum before. Fat browns=good,
Flat grays=bad. :D some tend to replace the little green "chicklets" also with Wima stack films, etc. But I haven't had one of those test bad yet.
 
I once saw such grey cap reported bad, I think it was on AK. There are two of those in Luxman l309v preamps. Mine were good, but it is remarkable seeing such again while you do not often see this specific caps. Apparently, most of them seem 1 uF 250V...
 
Lavane said:
It's been discussed in the Marantz forum before. Fat browns=good,
Flat grays=bad. :D some tend to replace the little green "chicklets" also with Wima stack films, etc. But I haven't had one of those test bad yet.
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Thanks Lavane. I don't spend enough time in the Marantz forum. Probably should read more there.
 
I'm a fan of Marantz separates of the 70's. I had collected and restore a few stacks. I've moved most of it along in the last few years after moving to tubes, but I did like working on most of it. I loved the symmetrical layout.
 
Lavane said:
the little green "chicklets" also with Wima stack films, etc. But I haven't had one of those test bad yet.
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i recapped my b&k amp not long ago and over half of those caps were brown from heat damage yet everyone tested ok. they got replaced anyway.
 
I believe one of these flat grays caused some damage in a Luxman tube amp but not sure. Know it was bad, though.
 
I've not had a film cap go bad other than to be completely open but I haven't run into this specific type either. Some of the "dog turd" caps used in Fisher gear would sometimes have the foil break loose from the lead and just go open or intermittent. I'm told that the tubular CeraCaps from the 60s had the same issue. Then there are those across the line Rifa caps that blow up from time to time.


oh, I'm lying, I did have a yellow cap short after I bumped it with a soldering iron, but that was kind of my fault.
 
After reading posts about these caps and finding a bad one myself, I just started pulling them when I found them. Most film caps hold up very well though.
 
Regarding "stacked caps": Just a bit of trivial pursuit (which I also posted in another thread from 2017):
  • " Sometime around 1960 one of the Cub Scout manuals had a basic "crystal radio set" build project using common household materials.
  • You made the capacitor by cutting small square pieces (I'm guessing around 1.5 - 2 inches) of aluminum foil and wax paper, then stacking them alternately. Leads must've been attached mechanically since we couldn't solder to aluminum. (Somebody obviously figured out the proper capacitance, which would depend on the surface area of the alumimun "plates" and the compression of the stack among other things; no doubt there's some complex formula to calculate this.)
  • As I recall, soldering was not required at all; instead, it used mechanical connections like wrapping wires around a binding post (here, a nail). Much easier and safer for a Cub Scout!
  • Tuning coil was wound around a toilet paper cardboard spool; it used a strip of sheet metal cut from a tin can for the slider.
  • Cystal holder was made from short stub of copper tubing mounted to board (as in original "breadboard" going back about a hundred years in homebrew electronics). Crystal was a piece of galena, and the cat wisker was a safety pin.
Unfortunately I don't have a copy of the manual to refer to, nor did my environment allow me to build this crystal radio set; otherwise I'd know a little bit more of what I was talking about! But yes, it was a "stacked capacitor" :). "
* * *
So, for you extremist audiophile electronics builders/hobbyists/enthusiasts out there wanting to impress your friends (and "Be the first on your block!") with esoteric one-of-a-kind hightest-end gear...why, you can handcraft your very own "stacks"! (Hmmm, now where'd I put that aluminum foil and wax paper?)
And finally, as Colombo would say, "Just one more thing"...Which is better, Reynolds Wrap or just plain ol' cheap generic stuff from the Dollar Store in terms of ESR, illegal transient ion migration, coefficient of dialectric vs. plate thermal expansion, etc. etc.? Inquiring minds want to know.
 
Dunno, I tried making one but I had the luxury of having a germanium diode, so having this esoteric piece it does not count.
It is how most extremists started and if it ends up tinkering audio stuff it is pretty harmless.:rflmao:
 
not sure the foil thickness would really affect it so much, but the thickness and quality of the wax paper would. If you wanted to go nuts you could experiment with different types of paper, plain, waxed, oil dipped, etc to tune the sound of your AM detector.

if you really want to go "foxhole" style, a rusty razor blade also works as a detector
 
gslikker said:
Dunno, I tried making one but I had the luxury of having a germanium diode, so having this esoteric piece it does not count.
It is how most extremists started and if it ends up tinkering audio stuff it is pretty harmless.:rflmao:
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The crystal radio I built as a kid used a germanium diode also. It worked pretty well.
 
On surfboards, they use "sex wax" to avoid the board surface to be slippery. It is rather sticky and probably well suited to make capacitors. (accidentally disclosing the secret sauce audiophile caps use)
 
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