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Antrecords's picture

Music Man HD150 2275 multiple issues + voltage chart

Hello, new to this forum but I really like what I see and have read so far. Seems like a real positive community based on sharing knowledge and experience on these slightly rare amps. Thanks in advance for any insight, etc.

I've been battling this 2275 for a bit here, it's had multiple problems and some rabbit hole type things. The complaint was lower than normal volume, intermittent/blown speaker sound. After a while I was able to narrow down the deep switch being crackly with certain vibration.

I could never get Q5 & Q6's emitters to even out, one was always around 25mv, the other 10/20mv more (in all combinations of tubes, with different transistors, updated caps).

The output transformer reads uneven with 680mv signal into the secondary, measured blue and brown primary leads to CT (6mv, 15mv). I have a feeling it has a few windings shorted across on one side.

I've created a voltage chart which I hope will be helpful to others. I'll correct it and repost once the amp is back up and running. This is with 2 6L6's right now, 690mv input, pre volume 6.5, master volume 7.5. All circled components tested or replaced. The amp sort of works, it's loud with the master cranked, but has lower than normal volume around 6/7.

Does anything stand out? Anything some fresh eyes can catch? Output Transformer?

full resolution: https://i.imgur.com/fcjXfop.jpg?1