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Wright Mono 8 Schematic & MQ Iron

Posted by jdrouin (A) on September 15, 2017 at 09:28:04

I'm posting this here because MQ used to supply iron for Wright Sound products and my question pertains, in part, to the amount of DC current that can reasonably be used in the FS-030. I've been breadboarding 300B circuits and am curious to try the Mono 8. Some of you knew George, so perhaps you can shed light on the early Mono 8 circuit (5Y3, 6SN7, 300B, MQ FS-030), or perhaps Mike knows what some of the specs and op points were?

Does anybody know the amp's operating points, have a schematic (George never wrote them down, but maybe some of you have drawn one?), have pics of the inside of yours that you could post/PM/email, or perhaps have info in old emails?

Reverse-engineering the circuit from the only internet sale pics I could find -- well, *a* circuit, since it may have been modified -- has left some puzzles that I'm trying to sort out.

* The 300B uses a 750 ohm cathode resistor, which is low for that tube. Using that resistor, the most reasonable operating point I can come up with in LTSpice is 300Vak @ 77.6mA (see attached image). That might approach the 7W output power that George claimed, but is 77.6mA too high for the FS-030, which on Mike's old site was rated at 70mA?

Other questions pertain to cathode resistor and cap values in the 6SN7 that are difficult to read in the pics, but I'll keep it simple with just the op points for now.

Thanks so much for any insight you might be able to provide.

Jeff

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