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A dumb question about the ritual of recapping a vintage receiver/amplifier


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OK, I understand recapping speakers and have done a number of them now successfully. But I also read about the necessary/obligatory recapping of older receivers/amplifiers.

Question: do you mean replacing every cap in the unit? Good grief. I look at a receiver and there are dozens of them, large to tiny. Or do you just mean the large ones in the power supply or tuner or pre-amp or...... which ones are generally meant?

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Hey red

I'm no expert in this area but here's my understanding: Yes. Replace them all. Yes, it's a royal PITA.

My thinking is, electrolytics go bad eventually (20 years? 30? 40?). I recapped my Mac4100 based on this thread: http://www.audiokarma.org/forums/showthread.php?t=176380&highlight=4100+recap (in fact I pretty much hijacked the thread) and also my Advent 300 based on Pete's thread here: http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=2778

Also, in my booklet on restoring the KLH Model Eight, I describe replacing electrolytics: http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=6387

As I understand it:

  • Only replace electrolytics
  • Use good quality (but not crazy expensive) caps. Nichicon and Panasonic are good. Nichicon makes different caps for different applications (I'll see if I can find a link)
  • For smaller values (maybe 2uF and under) you can usually substitute film caps
  • If you can't find the exact value, +/- 10% is fine
  • I try to use the next step up in voltage rating, but never go lower.

If you don't want to do all that you can always test a few of the caps and see if they are still good. But if you are talking about an amp from the 50s or 60s I think I'd ditch ALL the old 'lytics.

YMMV ;)

Kent

Here's the nichicon table: http://www.nichicon.co.jp/english/products/alm_mini/default.htm

If you look on page 2, you'll see for example that the KT series is hi-temp standard grade for audio equipment. KZ is premium grade for audio equipment, etc. They list 11 types for audio equipment. Mouser sells some of them and there are other sellers such as Handmade or Parts Conexxion that cater to the audio hobbyist.

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I'll weigh in here with some experience I've had and info picked up along the way. Some people feel you only replace failed or out of spec parts. Others point out that after 40 years caps dry out and drift in value, and that to recreate the original sound it's best to replace all electrolytics. Tantalum caps were also used sometimes and the general feeling now is that they should be replaced as well. Ceramic caps are left alone.

With receivers and integrated amps I've recapped I've sometimes heard quite remarkable improvements in sound quality...and sometimes not. Fortunately never worse! Restoration may sometimes cover more than replacing caps and includes replacing transistors that are known to get noisy or are prone to failure. There are experts in the various manufacturer's equipment who can help you out with this info, there is an amazing wealth of info on the 'net.

I think the place to start with is the power supply and then move from there to the preamp boards. Some people like to recap the tuner section, others advise against.

I do this as a hobby, and my aim is to restore and not just repair. I'm not an engineer, so I stick with the same capacitance values, and either the same voltage or slightly higher voltage. As Kent pointed out, Nichicon and Panasonic make good replacement caps, these are the most commonly used. And so yes I replace all of those caps...but if you do them one at a time it ain't so bad :-).

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Tantalum caps were also used sometimes and the general feeling now is that they should be replaced as well. Ceramic caps are left alone.

Good points. Also leave film caps alone.

I recently recapped a DB-1 preamp and it had some tants so those were replaced with film caps. Same goes for the Mac I mentioned above. As I understand it, tants are excellent while they work but if they fail can cause major damage.

Inspired by this thread I just placed a Mouser order. They carry the new Nichicon KA series caps, which are high temp, "for high grade equipment." CSP member and esteemed EE prof John O'Hanlon had advised me to use 105 degree C caps whenever possible so the KA seemed like a good choice.

When I did the Mac I used some Nichicon Muse bi-polar caps in places that originally had polarized caps. Only did that because that's what the original poster, Whaleman, recommended but I've heard conflicting advice on whether polarized caps should be replaced with NPEs. Of course the film caps are non-polar, so I suppose it's OK.

Eagerly awaiting the package from Mouser. I'll be recapping a DB-9 headphone amp (just 6 new caps) and an AR-SRC remote control (lots of caps in there but not nearly as many as a receiver).

Good luck!

Kent

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