http://db.audioasylum.com/cgi/m.mpl?forum=tubediy&n=59322&highlight=Building+Valve+Amplifiers&r=&session=

Well, it can be - but all the parts of the project must be worked out in detail, and good order. It can be simplified - without CCS, PP grid choke and fixed bias, but... If we use fixed bias we must have a negative bias supply and bias pots. Power supply is not present on the original schematic. If we have the PT with additional 50-60V "bias" winding, we can use it with Graetz bridge for the bias voltage, plus additional filter for the CCS. We need HV winding of about 350V-0-350V or little more, rectifier tube and choke input filter. Probably another LC filter for the front end. Ideally, four 2,5V/2,5A windings, too, 5V for the rectifier and another 6,3V for the driver...

Now that is not to say everybody needs to be able to design Doug's amp themselves to be qualified to build it but IMHO you should at least have a grasp of what each part is doing and why it is in the circuit. Or to put it another way, how can you be sure what you built is safe if you don't know what half the parts are and what they are doing in the circuit? Doug is a nice guy and all but you owe it to yourself to be able to double check his work and see that it is safe (I am sure Doug would agree and not take offense at this comment).

So no, tube audio isn't a "novice" thing. Guess that means you are not as much of a novice as you think you are huh?

The Seth is "simpler" on paper. I got to hear one at my house last night but I can't comment until the other mono block is done and I get to hear it in stereo.

Russ

Have your friend email me, I have a neat and useful improvement to the circuit. One of my mates up here has built a pair and reported favourably on the tweak. It is also free.

For manualblock, the Seth is a simple PP 2A3 circuit. Peerless S-240-Q output, phase splitting choke, and a high gain triode driving one end of it. CCS or resistive parafeed drive to the choke which is attached to the 2A3's grids. One of Magnaquest's distributors dreamed it up. It became viable with the modification to Mike's EXO-173 he and I worked out. I published a frequency response table on the prototype( on AA's Tube DIY ). Since I like doing the phase splitting with a tube( tubes actually ), I was never happy with driving an interleaved CT choke with a balanced drive. Some experimentation I did indicated it was likely due to the added winding capacitance the interleave caused.

For a 2A3 driving a less-than-flat speaker impedance, 6k6 is a better a-a load. If you want to stay in the Peerless 20-20 series, the OPTx in question goes by S-230-Q. This is the OPTx I am going to get wound for my wife's 2A3 project, Galahad. The Peerless spec on idle current is 70 mA/leg which is well within the 2A3's 60-65 mA idle current.
cheers,
Douglas

I am going to lay it out, and drill most of the holes, but my wife is going to do the rest. There isn't too much that I or somebody else on the forum can't answer as far as detailed questions go. troubleshooting isn't going to be an issue for some complex NFB compensation issue because there isn't any in Galahad. It's all open loop. Which is why I specified 6k6 instead of 5k a-a load. Slightly better damping from the bigger a-a load.
cheers,
Douglas