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#1
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Heathkit AA-121 feedback cap question
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 |
#2
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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 |
#3
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Hi RATs!
Unlike global negative feedback, upgrading the caps may improve your pleasure without hidden costs But, be sure you have the speakers you really like, if not deserve, before you spend time and money on other portions of the system. Happy Ears! Al Alan J. Marcy Phoenix, AZ PWC/mystic/Earhead |
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