Here is a balanced push-pull mic amp / driver design for use with a D104 or other balanced mics to drive tubes such as 810's, 811's etc. It also features AVC control. The neat thing is it has full push-pull voltage swing via the first stage and that eliminates problems when using single ended stages because you don't need any interstage transformers. The 2nd stage also acts as a compression / AVC control stage. That means you can have the exact same peak-to-peak output voltage level at the final modulator tube grids with low level voice tones and high level voice tones both Anyway, I will be modifying my current speech amp driver to the circuit above in my HB transmitter. Most of the values in the drawing should be correct or pretty close and I will post an updated drawing when finished if anything changes. .