Thanks to Suncalc for this link:
http://www.tubebooks.org/tubedata/RC30.pdfIt's an awesome book.
Based on the information in the book I was able to determine a couple of important things about the GM70. I'm on fire today!
First, the output power in SE mode will be about 30 watts at roughly 4 or 5 % distortion. Two tubes in paralell would yield at best 50 watts, again with about 5% distortion. This also involves a very large, very expensive transformer.
For class A PP, the output is more than twice that of a SE stage. It's more like 3 times the power. The really nice thing is the transformer is a lot smaller and less expensive.
I also found out that the load resistance for PP can be less than for SE (as seen by each tube) because of lower distortion due to the cancellation of even harmonics in the PP output. The lower load impedance allows more power to be extracted from each tube from higher current. It appears the Edcor transformer I ordered will be ideal for the GM70.
I calculate the output power to be about
85 watts per channel with low distortion for a GM70 PP class A pair. With the output trannys at less than $100 and GM70s going for about $60 a pair shipped to your door this is starting to seem too cheap and easy. The
800VA toroidal power tranny that will give me a B+ of 1130 volts was only $90 on ebay. The total cost of iron for this project not including shipping is less than $300 for an 85 watt/channel amp. Not bad at all. Even better, the total cost of tubes will be about $130. For caps I'm using 3 series 450 volt rated caps on the PS, so there's not a huge expense there. The interstage PIO caps were only a few bucks each.
There's a TON of very practical knowledge in that book. Thanks again to Suncalc.
This amp is going to rock.