Hi,
I guess close enough. I thought the 12VAC trannie would be a good clue. Push-pull 6AS7 (not P-P parallel though) class A with 6SL7 SRPP driver and digital input and volume control. No phono preamp at this time, but one could be added easily. The ground lug is because I have ground lugs on everything that connects to other gear. Mono blocks are the exception. Since this thing connects to sources like my tape head and phono preamps it will need to have one. Some folks say it is optional...you could fool me as in my system they always result in lower hum and noise. It is set up to be driven either by the internal volume/selection controls or an external set like my existing system preamp.
How does it compare....hard to tell since it isn't finished yet. Expectation is that it will do around 10 watts RMS and respond from below 20HZ to way past 20K. Distortion and S/N are probably in the Oddwatt range of 0.5% at 1/2 power and just at 2% at full power what ever that might end up being at a S/N at 1 watt of about 90db. The extra octal socket on each side is a carry over from early designs and uses 6NO60 delay relay "tubes". I can use them to switch the B+ going to the filter string directly without helper relays. That is because the B+ is only about 165 at the first filter and about 200ma per channel. Well within the ratings for the "tubes". BTW...they are now rather scarce and few reasonable vendors have them at reasonable prices. I have 6 now and will probably use them in future projects ...the average cost was about $10 each (they were common and only $5 when I first used them). Some folks are selling them for (gads) $140 each. When I run out (they are in my 4 existing mono blocks as well) I'll go to the LM555 timer used in the KT120 amps. It actually works better...but is not nearly so cool.
It is just what I really needed....I have far to many amps now, but it is a interesting diversion into P-P triodes.
BTW...I am not noted for doing things half way...but a 40 pound headphone amp is a stretch even for me
Good listening
Bruce
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FAQ
The 6AS7 can not be used in this type of circuit. The actual stage must have gain. With an amplification factor of only two it doesn't in this circuit. An overall gain of at least unity is needed and preferably more. As shown it has a gain of 0.3 approximately. What happens is for every three volts of drive there is only a change of 1 volt on the cathodes. Thus the second tube does not get proper drive. Cranking it up causes the driven tube to go non-linear while the second one is still not really pulling much of a load. Something new to add to the knowledge base.