Converting an 11m CB to Amateur Use: 10m Fun with General Electric (Part 3: Modification to 10M; RX and partial TX tuning)

 Today I followed the modification steps and success!  The radio is now on 10m.  Quite straightforward in two general steps:

RX adjustments

These went as expected: T1/T2/T6/T5 were tweaked, after I first adjusted L1 so the VCO lock voltage stayed between 1.5V and 4.0V on all 40 channels (now of course shifted up to 10m).

Beyond the mod prescription, I discovered by reading the schematic that one can adjust the S meter through potentiometer RV3 to be exactly on S9 when fed -73 dBm on channel 20 [29.125 MHz].  Here's how the S meter tracks after this adjustment was made starting at S9 and going downwards:

Not bad for a traditional analog circuit.  As expected (and unlike SDRs), it grossly undervalues signals beginning at S6 or so - e.g. the meter would have you think the signal is -91 dBm when it's actually more like -86 dBm.  

TX adjustments

Bill N2CQR un-confused me when I couldn't find adjustment coil L5, because this radio doesn't have one!  After adjusting L2, T3, and T4 as indicated, I got to Vpp = 30.4V which works out to (30.4)**2/400 = 2.34 W carrier.  Sadly, I don't have the right hex slug tuning tools, so those are now on the way in the mail and then I can get to the final 4W carrier = completion.

When that happens, potentiometer RV4 can be adjusted to make sure the meter just touches the "red" zone when PTT is pressed but no audio is going in.  That behavior will be consistent with how it was originally, unmodified.  

PS

By looking at the output on a KiwiSDR (LSB enabled), I could hear the carrier frequency in audio and then could adjust a signal generator on AM mode to match the tone when enabled/disabled, allowing me to read off the actual TX frequency.  For 29.125 MHz, the carrier is only 400 Hz off.  That's 1 part in 10**5.  Good enough for AM work!