I want them because I need to repair a couple of these, not that it really matters.
And what is "good enough?" I could take the time to map out the whole amplifier, figure out the differences between what they sent and what the amp actually is because they are not the same, and I could do the math and calculate the voltages. However, with schematics like one typically finds in in a service manual, it would be much easier. That is why I asked if anybody had a set.
I never understood why people feel the need to respond when they have nothing worthwhile to offer
And what is "good enough?" I could take the time to map out the whole amplifier, figure out the differences between what they sent and what the amp actually is because they are not the same, and I could do the math and calculate the voltages. However, with schematics like one typically finds in in a service manual, it would be much easier. That is why I asked if anybody had a set.
I never understood why people feel the need to respond when they have nothing worthwhile to offer
Yes this schematic looks far from correct, according to what I have seen on a 211M quite some time ago. Cannot recall all but a few notes I can point out:
- There're local feedback here & there: between the 300B driver and the 12AU7 PI, also between the 845 and 300B, apart from global NFB
- Interstage transformer is used, instead of plate choke & coupling caps shown on schematic
- V1B on schematic looks sketchy
- with the pinout shown, looks like V1 & V2 is 6SN7 whereas in my case they are 12AU7
- V2 PI use a longtail pair, with the tail goes to negative supply where it shares with bias network
- there was no bias adjustment in my case, instead there was a fixed zener network, iirc it was minus 150V
- apart from the signal chain with lots of details, the PSU is pretty straight forward and simple:
- a FW rectifier plus CRC filter for 845 supply
- another FW rectifier plus CLCRC filter for 300B and input stages
- a fixed zener minus voltage supply for bias
- a shared filament supply for both 845s
- a shared filament supply for both 300B
- a shared heater supply for the 12AU7s and magic eye tube
The ones I have are different than what you describe. The more I've looked into this it appears they changed things as they went along and didn't bother to document much of anything. This one uses a 6SL7 and an EL34, has adjustable bias on the 845s (circuit is smoked on one of them) plus many differences from the sketches they sent and what you describe.
In any case I appreciate you taking the time to respond.
In any case I appreciate you taking the time to respond.
I remember, perhaps 10 years ago, we had a meeting of the New jersey Audio Society at Audio Connection here in Verona NJ. Dennis Had was there as a guest and a pair of these 845 power amps were being used. I think the owner John Rutan carried Cary Audio back then. Anyway, I asked Dennis about the design of the amp's 300B driver stage and he told me that the 300B's were capacitor coupled, not transformer coupled as it appeared. He specifically said that he used a push pull output transformer to feed the 300's. I then asked if the secondary was terminated and he replied no it was just left unconnected or floating. I was surprised and he replied that of course if it was terminated he could get more power but would "loose the magic". I took this to mean fidelity and sound quality. Obviously Dennis has some odd design ideas.
