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In Reply to: RE: Received my new M-60s today. posted by pathologymd on April 13, 2016 at 15:37:20
pathologymd:
"Definitely a thing of beauty." Yes, it's certainly neater and more attractive, top and bottom, than my earlier ones were."Hmmm. What is the purpose of the bridge with the 2200uF caps behind the fuses?" I have no idea right now; don't have a current schematic. Caps are only 16VDC.
"I don't recall seeing that little circuit board either!" Me too. I think it's some kind of regulator; the devices have 3 pins. One wire is labeled 'cathode'; another is labeled 'coil', but I don't see one of those.
Output-stage caps are Nichicon 2200/200s, 35mm OD; can't see the model designation. Total OS capacitance is (6 X 2200 =) 13200uF. The schematic for a Mk.II.3 shows (6 X 1500 =) 9000uF. My old Mk.3.1 with large-PS option had (12 X 1800 =) 21600uF. I'm fantasizing about substantially improving the quality of those caps. I have 24 BlackGate VK-series 470/160s for (12 X 470 =) 5640uF per amp; probably I'll use something larger in the 1st-two cap. stages of a CRCRC filter. I also have 16 BG VK 150/350s to replace those axial-lead caps in the front-end HV supply.
We'll see.
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Tin-eared audiofool, large-scale-Classical music lover, and damned-amateur fotografer.
William Bruce Cameron: "...not everything that can be counted counts, and not everything that counts can be counted."
Edits: 04/13/16Follow Ups:
Unless I'm mistaken, Ralph is liking the idea of a solid state constant current source. There are a great many plus'. Though I can't remember what they are?.
The biggest advantage, and this is huge, it frees up a 6SN7. Your M60 now has two input tubes, like the MA-1, I think?.
If I'm not mistaken, this drops distortion to really low levels.
It still has four front-end 6SN7s, and AFAIK, they're configured the same way as they were in the Mk.IIs.
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Tin-eared audiofool, large-scale-Classical music lover, and damned-amateur fotografer.
William Bruce Cameron: "...not everything that can be counted counts, and not everything that counts can be counted."
I've been trying to think?
If the CCS is now solid state, what would Ralph use that spare tube for?
I looked closely at your 'inards' picture.
If you look closely, the signal wire from the XLR connection goes to a tag strip.
From there the signal goes through two input resistors. These are attached to V2.
There are two wires which connect those two input points to V4, also input points.
If someone else could look at the picture, that would be much appreciated.
If someone else could look
The MA2s that I repaired years ago had paralleled tubes for the bottom part of the cascode diff. So it looks like the two side tubes are the lower part of the cascode, the middle tube is the upper part of the cascode, and the front tube is the cathode follower/driver tube.
Craig
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