Re: Armstrong 621 and 625 rebuild and transplant
I would concur regarding the output and smoothing caps. I have been trying to solve a buzz/hum in one channel on my 625 and discovered that several of the electrolytics on the amp board were beginning to weep so I replaced them all. This has helped but not completely solved the problem.
When I reassembled it, it had a hum that varied with the volume setting. This turned out to be the position of the leads from the pre amp board to the main amp board. They need to be run in the "well" in front of the main board otherwise they pick up hum from the mains components. I think that screened leads would have been a better choice here.
As all the electrolytics are the same make then you could consider replacing them all for long term reliability but otherwise I would leave well alone as it sounds great to me as it is.
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Paul
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