Total posts : 45366
Thank you Neil for your scientific observations. This information could be useful to others because the AM25 transmitter is still available from Ramsey.
I pose to you my belief that the Manual contains an error which can be proven by comparing two different statements:
1.) On page 5 in the Circuit Description I quote one line – “The main disadvantage of high level modulation is that the modulator’s power must be half that of the final transmitter.”
2.) On page 19 under Alignment Procedures “(7) Measure the voltage on resistor R34’s lead closest to C23. Adjust ‘Bias’ pot R23 for 7.1 VDC.”
I’ll let you conclude why both of these statements cannot be true at the same time (except, of course, when the final voltage is 14.2 VDC).
Moving on, I believe the question you raise about the precision of the bias circuit is worth considering. Where you find one error (the manual?) it’s likely there could be others.