[TV MAN]

Ok, so I tried an experiment tonight. I put a switch on to kill the feedback or keep it in the circuit. Result? FAIL! That's a no-go. I thought it was great for a moment as the gain was tremendous and the highs and mids came alive, but so did the distortion, hum and all kinds of noise. Probably OK for a guitar amp, but on this HiFi amp, noooop. I also added a really cool Johnson Cinch jack to fill in an extra hole over the bias pot that I can use to check the bias voltage right on top of the chassis. So that experiment is a success. Once the current is set, you can check the voltage too. I have the voltage at -26.4 and current is about 30ma idle each tube. It's weird how the tone changes when you adjust this. This seems to be the sweet spot. It runs cool and had plenty of punch. It's really almost to the "leave it alone" point, and start on the next one. It's working really good right now. I almost hate to mess with it any more.

EDIT: The switch I added to turn on or off the NFB might actually not be a total failure. It could be used to help weed out marginal or noisy driver tubes. I note this in that some of the common 6GH8a's are noisy.

   

Sooo - at this point, time to start building it's twin sister. Now that I have the build down, I will try some more experiments as I go together with this one. Gonna try a better step bit and see if I can enlarge a couple tube holes for the octal sockets. I might attempt using a chassis punch, but not holding my breath that it'll work. If not, then I'll grab the die grinder and do a little more "redneck engineering"