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Hello and thanks for looking. This amp just might be designed like no other I've seen. I've been reading the schematics, studying up on old posts, read "lessons"...I've also read/posted to the MM forum which seems like a great resource. I'd like to contribute a schem/voltage chart to the forum for future reference/people going down the rabbit hole I've been stuck in for a while. Here's the first pass:
The complaints on this amp were blown speaker sound and volume loss. I feel like I've shored a lot of that up. Going rounds I was thinking filters, tubes, OT's...but the related issues I found were intermittent impedance selector, scratchy deep switch with frequency vibration, maybe actual speaker rub though I haven't seen them yet.
I've tested, A/B'd or updated way too many components, in a good learning curve way. The dc voltages now look pretty correct (replaced 22v zener). I'm still going to do the filters, some electrolytics.
The problem is the volume doesn't get going until the Master is on say 8-10. I think this is a part of the original complaint but I'm not quite sure. It'll still clock around 130w RMS, 175w cranked. Seems pretty good for old filters and existing tubes. But it's much lower volume from say 1-7 on the Master. All the taper is at the tail end. Is it broke? Is it design? I feel like I'm in some gray area.
This is where some expertise on these models can be of assistance. How does the schem/voltage chart look? Anything jump out as funny business?
The input is 680mv, volume on 6.5, master on 7.5, AC in red, DC in green. Anything circled has been tested, A/B'd or replaced.
More gray area, I've juggled the tubes, done one at a time in different positions, old tubes, new tubes, I don't ever feel I can get the emitter/3.9ohm voltage to quite balance (25mv, the other side is always higher, say 10-15mv). I've rebuilt most of the driver board trying to get this balanced. It does sit in the 25-45mv guideline. I'm saying I can put the same single tube in socket 1 or socket 4, it reads different. And I've also addressed all the circled components. Am I overlooking something?
Any feedback or similar experience on this one much appreciated.
The complaints on this amp were blown speaker sound and volume loss. I feel like I've shored a lot of that up. Going rounds I was thinking filters, tubes, OT's...but the related issues I found were intermittent impedance selector, scratchy deep switch with frequency vibration, maybe actual speaker rub though I haven't seen them yet.
I've tested, A/B'd or updated way too many components, in a good learning curve way. The dc voltages now look pretty correct (replaced 22v zener). I'm still going to do the filters, some electrolytics.
The problem is the volume doesn't get going until the Master is on say 8-10. I think this is a part of the original complaint but I'm not quite sure. It'll still clock around 130w RMS, 175w cranked. Seems pretty good for old filters and existing tubes. But it's much lower volume from say 1-7 on the Master. All the taper is at the tail end. Is it broke? Is it design? I feel like I'm in some gray area.
This is where some expertise on these models can be of assistance. How does the schem/voltage chart look? Anything jump out as funny business?
The input is 680mv, volume on 6.5, master on 7.5, AC in red, DC in green. Anything circled has been tested, A/B'd or replaced.
More gray area, I've juggled the tubes, done one at a time in different positions, old tubes, new tubes, I don't ever feel I can get the emitter/3.9ohm voltage to quite balance (25mv, the other side is always higher, say 10-15mv). I've rebuilt most of the driver board trying to get this balanced. It does sit in the 25-45mv guideline. I'm saying I can put the same single tube in socket 1 or socket 4, it reads different. And I've also addressed all the circled components. Am I overlooking something?
Any feedback or similar experience on this one much appreciated.
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