I recently built a Ramsey AM25. All parts are in the correct places. There is very low RF out of Q3, and drive going into Q3 is higher than what comes out. I have replaced Q3 and no change. I am stumped. I work on transmitters more complicated than this, I shouold be able to figure it out. Anyone heard of a similar problem?
I recently built a Ramsey AM25. All parts are in the correct places. There is very low RF out of Q3, and drive going into Q3 is higher than what comes out. I have replaced Q3 and no change. I am stumped. I work on transmitters more complicated than this, I shouold be able to figure it out. Anyone heard of a similar problem?
Did you see my post regarding this on the other forum?
If not, it is reproduced here for your consideration.
Reginod,
Please don't be insulted, but is it possible that you have the FET (Q3) and the BJT (Q9) transposed? They both look the same and you might have them mixed up.
Otherwise, here are some data I took on my AM-25 when I did a load test. I set R23 to give 7.1 volts at the R34 lead closest to C23 (per the manual). With a 50 ohm dummy load on the antenna output and no modulation, I measured:
Voltage across R34 = 2.73 volts DC. (with a DVM).
Voltage at Q3 Drain to gnd. = 1.63 volts DC. (with a DVM).
Voltage across the dummy load = 2.48 volts RMS (with a Fluke 123 scope). Very nice looking sine wave.
I hope this gives you a benchmark to begin troubleshooting.
Neil
It would help us help you if you make these measurements and report your results here.
Neil