Hi Don - thanks for your speedy assistance.
To be clear - what I am hearing when I transmit SSB is RFI - loud garbled sounds from the speaker or headphones, not a clear rendition of my voice.
The offender seems to be the wiring to the volume control (audio). If I unplug the audio pot from the audio pins on the board, the RFI goes away. I am using a twisted pair from the pot to header pins on the AGC board.
With the pot connected, the RFI is heard when I transmit into a dummy load or an antenna, no difference.
Independent of the RFI, I noticed my use of J1 to drive the S-meter was giving a reading of zero. I checked the voltage on J1 (with everything hooked up to the AGC board) and it never deviates from zero, so I must have a problem with the AGC board. This happens even if I disconnect my AGC off/med/long switch and just check the voltage at J1 - it's zero regardless of signal level.
So I think I have (at least) two problems - RF being picked up by the cable going to the volume control pot, and something wrong with my assembly of the AGC board so there is no voltage across C4.
I'll see if I can re-route the audio cable - I was trying to keep it on the short side so it is routed across the board, not along the case as you recommend. I'll try that.
I do have a second AGC kit so I can try assembling that and see if my "no voltage across C4" issue goes away.