11-25-2015, 08:35 AM
Progress report:
One bakelite block that I didn't get (that I thought I had) solved both the nasty clipping AND the poor AGC action. Block was #79, filtering for 1st audio suppressor and grid bias. Basically, what I think was happening is that at low volume, things behaved more or less normally, but as I increased the volume, the audio signal was modulating the suppressor grid as well as control grid bias, so it was clamping the plate signal by feeding in an out of phase signal.
Scope attached to plate of 1st audio, radio tuned to 1700 KHz, generator at 1700KHz with 400Hz tone.
Audio from my inhouse AM transmitter at 1620KHz. (thank goodness for the Police Band on this set)
Audio is now beautiful, though I still have a few paper caps to replace, but mainly these are in the tone control circuit.
LO is still DOA on the AMBCB. All other bands it works great. Still driving me crazy(er). Afraid I'm going to have to pull the LO coil so I can check for problems. Can't see anything wrong with the bandswitch, but that may be just the limited view I have of the LO section of the switch.
Any ideas on that, Ron?
One bakelite block that I didn't get (that I thought I had) solved both the nasty clipping AND the poor AGC action. Block was #79, filtering for 1st audio suppressor and grid bias. Basically, what I think was happening is that at low volume, things behaved more or less normally, but as I increased the volume, the audio signal was modulating the suppressor grid as well as control grid bias, so it was clamping the plate signal by feeding in an out of phase signal.
Scope attached to plate of 1st audio, radio tuned to 1700 KHz, generator at 1700KHz with 400Hz tone.
Audio from my inhouse AM transmitter at 1620KHz. (thank goodness for the Police Band on this set)
Audio is now beautiful, though I still have a few paper caps to replace, but mainly these are in the tone control circuit.
LO is still DOA on the AMBCB. All other bands it works great. Still driving me crazy(er). Afraid I'm going to have to pull the LO coil so I can check for problems. Can't see anything wrong with the bandswitch, but that may be just the limited view I have of the LO section of the switch.
Any ideas on that, Ron?
