Meck XB-702 restoration

[Kevin Kuehn]

Originally Posted by bandersen

Interesting results with a 1M cathode resistor. The gain does drop, but the grid is far less sensitive to external noise. However, there is still a buzz present. Grounding the grid does nothing to reduce it. Grounding the cathode reduces it by about 50%.

I'll continue to experiment.

1meg is way to much for a cathode bias resistor, as there's only 390k in the plate. If you look in the back of an RCA tube manual they'll give recommended values for resistance coupled amplifies, and I'm pretty sure you'll find the 6AT6 included in one of the charts. You may also reduce the value of the plate resistance. The idea being to reduces both the impedance and gain of the stage. Just a guess would be about 5K in the cathode if you leave the plate resistor alone.