I have an RCA AM/FM Set 68R3 (Chassis RC608) (Rider's Vol 16; Pages RCA 16-39 - 16-42). I have recapped it and replaced the out of tolerance resistors and it plays beautifully on AM. On FM it catches the band from about 102-108 across the first 20% of the dial, then nothing. I took a shot at the alignment procedure from Rider's with no improvement (I have an Eico 315 Sig Gen that goes up to 150Mhz). I've tested all of the tubes-ok. Anybody got any ideas?
Thanks, Jim

Hi Jim

Try another 6BE6. Since you have two in this radio could reverse positions? A 6BE6 oscillator can test good and still not operate properly on FM.

Norm

:I have an RCA AM/FM Set 68R3 (Chassis RC608) (Rider's Vol 16; Pages RCA 16-39 - 16-42). I have recapped it and replaced the out of tolerance resistors and it plays beautifully on AM. On FM it catches the band from about 102-108 across the first 20% of the dial, then nothing. I took a shot at the alignment procedure from Rider's with no improvement (I have an Eico 315 Sig Gen that goes up to 150Mhz). I've tested all of the tubes-ok. Anybody got any ideas?
:Thanks, Jim

Jim,
I agree with norm, if swapping the tube doesn't work, your OSC circuit is the problem. WHat I do is inject the desired frequency to the antenna port modulated with a 1Kc tone and tune the dial to the injected freq. Try the freqs that do work and then inject the freqs that don't work and you can see the difference. In your case, the IF section IS working since you can tune on certain freqs (IF is constant) which narrows it down to the OSC or the front end. Almost sounds like a cap or resistor is WAY out. Most likely in the OSC circuit (IF TUBE is good).

Joe

:Hi Jim
:
: Try another 6BE6. Since you have two in this radio could reverse positions? A 6BE6 oscillator can test good and still not operate properly on FM.
:
:Norm
:
::I have an RCA AM/FM Set 68R3 (Chassis RC608) (Rider's Vol 16; Pages RCA 16-39 - 16-42). I have recapped it and replaced the out of tolerance resistors and it plays beautifully on AM. On FM it catches the band from about 102-108 across the first 20% of the dial, then nothing. I took a shot at the alignment procedure from Rider's with no improvement (I have an Eico 315 Sig Gen that goes up to 150Mhz). I've tested all of the tubes-ok. Anybody got any ideas?
::Thanks, Jim

Jim,
Another thought, if you have a cap meter, make sure your tuning caps (ganged caps) for FM are working. A bent plate can cause this problem too. I usually put my cap meter across the ganged caps one at a time (rf and OSC) and make sure the value changes from one end of the dial to another.
Joe

:Jim,
:Another thought, if you have a cap meter, make sure your tuning caps (ganged caps) for FM are working. A bent plate can cause this problem too. I usually put my cap meter across the ganged caps one at a time (rf and OSC) and make sure the value changes from one end of the dial to another.
:Joe

:Jim,
:Another thought, if you have a cap meter, make sure your tuning caps (ganged caps) for FM are working. A bent plate can cause this problem too. I usually put my cap meter across the ganged caps one at a time (rf and OSC) and make sure the value changes from one end of the dial to another.
:Joe

It looks like the 106 Osc trimmer (C33 2.5-13mmf) isn't changing value when it is adjusted. I'm going to see if I can find one to replace it with.