Coupling Cap quality in 500-C? Max Voltage rating of replacements?

Discussion in 'Fisher' started by rufleruf, Nov 7, 2018.

  1. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    I am working on my most recent 500-C and I got to thinking about coupling caps. I am pretty sure I am going to go the 220K resistor / .068uf capacitor combo route on this one. I usually use those yellow Illinois caps or Orange Drops for coupling, but got to thinking about fancy caps.

    I am curious to hear from those who have opted for fancy capacitors for coupling caps and the results they got. I am leaning towards using some Russian PIO caps off eBay, but am happy to hear other options. Please post links to places to buy them if mention a boutique cap. I found an older thread that was talking about Mundorf Supremes, but I couldn't find any for sale in the sizes referenced. I don't mind spending $20 per cap for the sake of trying this out.

    Also, if I go fancy for the output tube coupling caps, wouldn't I also want to use similar quality caps through the whole signal path?

    Finally, I have some super high end mil spec Micamold insulated PIO .1uf x 600V 1% caps that all test dead on .1uf. If I was to use these, what would be the ideal resistor value?
     

     

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  2. notdigital

    notdigital AK Subscriber Subscriber

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    The .068uf Russian PIO's are not only an economical substitute for the originals, they work wonderfully well in the Fisher circuit. I wouldn't spend $ beyond that. Since you already have Micamold PIO's on hand, I'd save a step and use them @ 200k.
     
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  3. 1rebmem

    1rebmem AK Subscriber Subscriber

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    Matt,
    I ordered some Russian K40Y-9 PIO .068uF 400v cap's about a month ago and are due in within a couple of days.
    The size of them could be an issue as far as fitting them in place. They also have a metal case that I will put clear heat shrink on.
    When I get them I will post more info and maybe some pic's.
    Jef
     
  4. 1rebmem

    1rebmem AK Subscriber Subscriber

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    Seems to me, yes. Only as good as the weakest link kinda thing.
     
  5. gadget73

    gadget73 junk junkie Subscriber

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    I like basic film caps. They fit, and they work. The original ERO caps are not physically massive, so there likely isn't a ton of extra room to fit fancy caps in there. Most of the fancy ones are just huge for whatever reason.

    I'm also not a believer in capacitors having any real magic in the feedback loop, which is another reason I don't put fancy stuff in the power amp stage. Outside the feedback loop I've heard it, but never inside. The other night I installed the absolute cheapest film caps Mouser had in an amp, and it doesn't sound any different than when I had the big PIO caps that were about 10x the physical size in the circuit. The cheapos were Panasonic caps. I needed something of a given value and wasn't keen on spending a lot of money since they could be temporary.
     
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  6. dsndblm

    dsndblm AK Subscriber Subscriber

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    Another vote here for the Russian K-40Y PIO caps. They fit inside the 500C without issue, sound really nice.
     

     

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  7. bhamham

    bhamham AK Subscriber Subscriber

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    Another vote for basic caps. I like to use the original ero-fol caps if they test good and have plenty of spare ones to replace the bad. I've tried the Soviet PIOs, orange drops and others but to my ears they sound the same.
     
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  8. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Same here. If I have to replace, I'll use either C.D. DME Series Radials or Illinois Cap MKP axials. Sound difference is nil compared to the ERO-FOLS, and they are physically small. Larger caps also have a tendency to gather RF, so the smaller physically, the better.
     
  9. tcdriver

    tcdriver AK Subscriber Subscriber

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    Standard polyester caps in my Fisher 500-C. Matt, whatever you end up with I would like to know if you hear the difference and if so, what is the difference.

    FN-5B (800x366).jpg
     
  10. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    I love it when I come back to a thread I started and it's full of good info!

    Sounds like a lot of votes for "don't bother" but no experience with Mundorf gold foil platinum supreme snake oil and parchment with a twist of lemon caps.

    I ordered some caps from Russia yesterday - the seller on eBay cut me a bulk deal, so I have a nice round 100 PIO caps coming: 20x .022/400 40x .047/250 20x .068/400 20x .068/600. I'll do a full signal path rebuild of one of the receivers on the pile and report back in 3 months.
     
  11. gadget73

    gadget73 junk junkie Subscriber

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    Test them for leakage first. I haven't had a bad one yet but those caps are old. I have run those caps in places, but I'm impatient and I can get stuff from Mouser in 3 days vs 3 weeks from Russia.
     

     

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  12. 1rebmem

    1rebmem AK Subscriber Subscriber

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    So on this coupling cap question, what do you guys think about the ceramic caps used in the phono section and other places?
    Some people would NEVER allow a ceramic in the signal path.
    I'd like to hear opinions/experiences.
    Thanks.
     
  13. Jon Kasper

    Jon Kasper New Member

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    My understanding is that K40Y work very well for output tube coupling caps. But overall, it’s advantageous to use a variety through the signal path, a mix of K40s and polypropylene, so as to avoid the sonic signature taking on too much of one variety and to add elements from one type of cap that the other may be lacking in. To create synergy.

    I’m working on recapping my 400 now and replacing the .09 cent Chinese caps the original restorer used , and am using:
    - mix of Vit Q and K40 in phono
    - K40Y for output tube caps
    - Auricaps for input coupling caps
    - remainder of coupling caps being a mix of 716p Orange drop film/foil w copper leads & K40s
     
    Last edited: Nov 10, 2018
  14. 1rebmem

    1rebmem AK Subscriber Subscriber

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    Thanks Jon!
     
  15. 1rebmem

    1rebmem AK Subscriber Subscriber

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    tcdriver......Nice looking work inside your 500C!
    Jef
     
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  16. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    I am looking at some interesting coupling caps that are .068uf 1.6kV (pretty sure DC). Is there an issue going this much over the working voltage?
     
    Last edited: Jan 4, 2019

     

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  17. sgmlaw

    sgmlaw Well-Known Member

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    If you want to best approximate the original Ero-Fols used in the Cs, the closest I've encountered are Cornell Dublier miniature metallized polyesters. These are dirt cheap, rock solid dependable, and available in values up to 1kv last I checked. And they get about 98% of the way there. They are so close, it is what I will use in the earlier models and in the separates, too. A really nice vintage coupling cap. And they don't visually jump out of the chassis and scream 'hot rod job' either. A lot of others prefer the IC yellows, and they are ok, too.

    While I'll toss orange drops and polyprops in a B series on occasion to tighten up a flabby one, it always sounds too 'Hi-Fi' in a C series. I would stick with polyesters, PIO, or something along those lines in the later receivers.

    If you want to slightly 'improve' on the original polyesters, I like the Soviet K40y9 series, which will drag a C a little closer to a B, with a more airy, slightly less etched presentation. I always heat shrink these before dropping them in with some 3m clear, because the outer metal cases are so darn big, I'm concerned that some later hack is going to short on one.

    And if you want a C series on steroids, then the best I've heard in one of these is the AmpOhm Polyester in Oil series, which are now unobtanium. Everything in the original equipment, just really better. Vividly so in some instances. They can lift up a B,too. If you can find them, they are always worth a listen.

    I wouldn't go any more exotic than that in these. The important thing is that you get the original Ero-fols out of there pronto, as I have seen too many that start leaking a couple of volts after a few decades . . . and that is all it takes in one of these.
     
    Last edited: Jan 4, 2019
  18. sgmlaw

    sgmlaw Well-Known Member

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    651
    You will never need to drop anything with that high a WV in these. 600v is optimal on the HV side, and perhaps 1kv if you are paranoid.

    Purists sometimes like to not have too much voltage headroom in an electrolytic, as they will argue that it starts to compromise the efficiency of the capacitor. But I can't imagine any such consideration in any film type, other than that the cap is going to be relatively enormous.
     
  19. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    The caps I'm looking at are the ERO MKT/MKC/MKV series that were made in Europe until the early 2000's. They seem to have a lot of fans for audio use and are not too much $ when they pop up.

    Not that it really matters, but they have a pleasing vintage look to them reminiscent of the original ERO caps in the Fishers.
     
    Last edited: Jan 4, 2019
  20. sgmlaw

    sgmlaw Well-Known Member

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    In that series, in a Fisher C series receiver, my first choice would be the MKT.

    Don't fall for the polyester bashers and the exotics disciples. You'll wind up Dr. Stereoing the original sonics right out of one of these, if that is what you want to retain. The designers voiced their equipment very carefully around the materials then available. I always recall the story about David Hafler auditioning various coupling caps for one of his new amplifier designs. Even though there was every exotic copper and silver-leaded capacitor type available and tried, a simple steel-leaded 10 cent economy film capacitor always prevailed in every single listening test. So that is what he built the amp with.

    I encountered it myself first-hand about 20 years ago. I rebuilt our vintage NuTone master station after 35 years, and out of habit and because of what I had on hand, dropped a joe average polypropylene in it. Sounded absolutely horrible. The whole family complained non-stop about it. Finally dropped a rogue polyester close to the original back in, and every one was happy again. Go figure.
     

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