05-15-2016, 06:21 PM
Steve, regarding the problem with getting the RF circuit to tune, have you properly located the dial scale on the tuning cap?
From your description, it seems you have too much RF stage tuning capacity for a given receive freq, which is why your trimmer is all the way open and still wont peak. How does the dial freq calibration compare to the actual freqs of received stations?
It seems you need less tuning capacitance in the RF stage and since the trimmer is all the way open, the only other thing to do is to tune the tuning cap higher (less capacitance) and compensate with the oscillator trimmer so you receive the signal at the higher dial location. Sometimes you have to play with the position of the dial scale on the tuning cap shaft to compromise dial accuracy and tracking of the RF and Osc circuits.
The other thing to check is that the IF is accurately set to 460 kHz. You mentioned that you had to retune the IF as all circuits were off. Are you using a freq counter or a synthesized generator to accurately generate the IF signal? I would not trust a usual service grade generator to be accurate enough unless you are setting the freq with a counter.
From your description, it seems you have too much RF stage tuning capacity for a given receive freq, which is why your trimmer is all the way open and still wont peak. How does the dial freq calibration compare to the actual freqs of received stations?
It seems you need less tuning capacitance in the RF stage and since the trimmer is all the way open, the only other thing to do is to tune the tuning cap higher (less capacitance) and compensate with the oscillator trimmer so you receive the signal at the higher dial location. Sometimes you have to play with the position of the dial scale on the tuning cap shaft to compromise dial accuracy and tracking of the RF and Osc circuits.
The other thing to check is that the IF is accurately set to 460 kHz. You mentioned that you had to retune the IF as all circuits were off. Are you using a freq counter or a synthesized generator to accurately generate the IF signal? I would not trust a usual service grade generator to be accurate enough unless you are setting the freq with a counter.
