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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
The little circuit board is a 2-stage CCS circuit, replacing the 6SN7 2-stage circuit of older amps. It has better performance (although the older CCS performance was excellent); because the MOSFETs have so much more gain, they really can perform better in a CCS circuit. The circuit has the added benefit of really preventing any chance of filament/cathode arc-over in the voltage amplifier circuit although that really wasn't a serious problem with 6SN7s in general.
This freed up a tube socket, which is in this case paralleled with the original 'V1' tube sections, to allow the bottom portion of the differential cascode to better drive the top portion. This yields lower distortion and slightly more headroom out of the voltage amplifier.
The other device, the bridge with the caps on it, is for blocking any DC component that may occur on the AC power line due to electric heaters and the like.
Thanks so much for the information, Ralph.
Straight from the Ralph's mouth, about the M-60 Mk.3.3:
1. The old 'input tube', V1, is now two input tubes in parallel, labeled V1a and V1b. V1a is in the right-rear position (see picture) while V1b is at the left-rear. These two input tubes are physically separated by the...
2. Old and new V2 which I can never remember what to call this function--it's the Voltage-gain 'top' tube in the Mk.3.1 schematic I have. This is the rear-center tube and is the one that would be replaced with the gain-reduction plugs that A-S sells.
3. The good-old V4 cathode follower is in the front of the amp.
All of these in my amps are currently Tung-Sol roundplate 6SN7GTs. Those in the CF positions are my least-good tubes, low in transconductance and relatively high in microfonics--that in these CF positions are free of microfonic noise when tapped lightly with a pencil.
FWIW, even with only dozens of hours on new amps, new tubes, new Teflon-film coupling caps, etc., these amps have helped my system sound even better, particularly in transparency and spatial resolution. I'm very happy.
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."
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