[Radiodial]

I have no Bass amplification on the 37-690 I'm trying to finish up. 
All caps and resistors have been replaced
Known good 6K7G and 6J5G in place.
All the wiring around the 2 Bass Amp tubes have been checked and cross checked against the schematic.

That leaves signal tracing to find where the audio is failing. This thing should act like a basic amplifier circuit I suppose. 
I injected AF onto the wiper of the bass control (120). That worked OK.
I then injected the signal onto the grid cap of the 1st Bass amp 6K7G. A decent pop, but no audio.  That's where I lose the possible signal injection path.
Any tips on where to apply the audio signal to troubleshoot the Bass Amp section (lower right corner of the schematic)? Everything else in the radio works now.