[R-390] R392 help

[Drew P.]

Charles wrote:

"Finally, for reference purposes [only -- do NOT build one of these...],
here is documentation on the factory "transistorized amplifier module"

The modification using 2 bipolar transistors to replace the 26A7 audio output tube is GUARANTEED not to work correctly. It would have large amounts of crossover distortion due to no forward bias.  It may appear that the two 10k resistors to the transistors' bases would supply such bias, but the center tap of the transformer which feeds the bases is grounded and so would shunt the bias to ground.  One could unground the center tap and feed in the bias there (along with adding a bypass cap), eliminating the two 10k base resistors, or better yet, just build the MOSFET version which Charles recommends.

Drew