[HAM] Those Pesky Cathode Bypass Capacitors

[Keith H Clark]

The reason the bypass caps needed replacing was not that their capacitance
had dropped appreciably but that their ESR or internal series resistance to
the audio signal had risen enough to affect the sound.Keith

-----Original Message-----
From: hammond-bounces at zeni.net [mailto:hammond-bounces at zeni.net] On Behalf
Of Scott Hawthorn
Sent: Tuesday, July 22, 2008 12:14 PM
To: The Hammond Forum
Subject: Re: [HAM] Those Pesky Cathode Bypass Capacitors

At 09:06 AM 7/22/2008, David Anderson wrote:
>Scott,
>In your experience with rebuilding/repairing AO-28s, have you found
>that these bypass capacitors degrade faster or more often than the
>high voltage supply capacitors?
>
>The reason I ask is that in this 1970 preamp, just replacing the
>bypass caps really made the organ sound great. There is very little
>power supply ripple on the high voltage capacitors, ~10 millivolts.
>As I've said myself before, it's good to replace all these as a
>matter of routine maintenance, but perhaps the lower voltage sections
>just don't last as long.
>
>I'm thinking of doing my next preamp rebuild with all discrete
>capacitors mounted under the chassis. Sprague/Vishay, Panasonic,
>Nichicon, CDE, etc... all make electrolytics that measure better than
>current multi-cans, though the venerable Sprague Atoms have jumped in
>price of late.

I've never had any way of really knowing what the condition of these caps 
were. We pragmatic-types, when we're on the clock, just replace 'em. In the 
case of electrolytics, an exception is made to "if it ain't broke, don't 
fix it," because in this case, if it ain't broke, it soon will be after all 
these years. Sometimes the amp sounds better afterwards, sometimes, not so 
much. It's an interesting question to which I'm betting you won't find a 
definitive answer here. I do appreciate your thirst for knowledge. I dunno 
much; I just fix 'em!




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