Home AM Transmitter (again!)

[jr_tech]

A comment from the earlier thread about the very unusual operating conditions of this circuit:

old_coot88
Yeah, i thought about that too. But figured that the cathode being at `near` ground (except for the coil resistance) probably mitigates for the absent G2 voltage a little. Then with both grids at the same potential, the tube behaves electrically more like it's a triode running at lower power than a full-up pentode. Or at least that sounds sorta plausible.

Got to looking at the 117L7's spec sheet posted earlier, and it's classed as a beam power amplifier. If that's correct, it's a tetrode with beam-forming plates and there would be no suppressor grid (G3) between G2 and the plate. So with G1 and G2 "strapped" at the same electrical potential, the tube would be running as a "beam triode".

http://www.videokarma.org/showthread.php?t=251917
Still scratching my head...
jr