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John Stewart
 
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Kevin Killebrew wrote:

Hi,

I'm restoring my Heathkit AA-121, and notice that the cathode cap/resistor
network coming off the first 6AN8 contains a 50uf 15v electrolytic coupled
with a 680 ohm resistor, and then connects to the feedback loop going to the
OT secondary via another resistor/cap network. I hate the idea of any of
the signal path going through an electrolytic but am not sure if it's worth
replacing with a large (and expensive) film or poly type. I've seen some
Solen's and Dayton 50uf poly's commonly used in speaker crossovers that
might work/fit since there is a lot of room in the amp chassis. My question
is: Is it worth doing? The 50uf poly's are around $13 each. The money's
not a big issue, but I don't want to do it if it really doesn't matter. I
really do like this amp.

Kevin Killebrew
Austin, Texas


You have been listening to much to the 'boutique' audio end of the buz. It would
take a kilobuck's worth of equipment to measure the improvement resulting from
that change, if in fact there is one. For example, any of the tubes in the amp
have more non-linearity than that cap will introduce into the audio path.
Fortunately the applied NFB fixes many of the problems. If it were a serious
problem at the time of design it would have been fixed then.

Some people really think they can hear a difference. Biggest problem by far in
any of these systems is the loudspeaker(s) in it's box & the listening room.

But do it if it gives you comfort.

My 2 cents, anyway. John Stewart