01-22-2023, 01:01 AM
Very strange!
This radio has a tuned RF stage, but the Convertor is not tuned. Only the local oscillator is.
From what you describe, there may be an issue with the RF, but I think that the bigger possibility is the oscillator. It may be that your generator provided the frequency that heterodyned with the station that you picked up. If the station was loud, the RF Amp may be good.
If you get a strong station and change the SG freq what happens? I wander if U got the strong station due to a beat freq from that station's freq vs the SG Freq. Do this again with the modulator off. Is the frequency of the station read out correctly on the Radio's dial when the station is received under this condition?
Ordinarily, I would say to touch a long wire to the signal grid of the 12SA7 but since the stage is not tuned, that may not tell you anything.
How accurate is the SG? Check against a known station on a good radio, loose coupled to that radio's antenna.
Connect via a capacitor to the 12SA7 side of C5, set for 455 KHZ and rock the SG dial till you get a loud tone from the SG's modulator. That should tell you what the IF Freq is.
Either your IF is off, your local oscillator is off, or the local oscillator is dead.
Take a transistor radio, tune to a station about 455KHz above a known good station, turn the chassis upside down and hold the radio near the oscillator coil. Tune the CoRadio to the known good station and rock the tuner around that frequency. The other radio should squeal or get quiet when the known station is tuned. If there is no response from the test radio, the oscillator is bad.
If you get the squeal but at the wrong freq, you could try the trimmer on the oscillator section of the tuner cap. mark the current location and rock the trimmer. If no improvement, return to the marked position.
said earlier in this thread that there was little difference between the various AA6 sets. This is me eating my words, as I have never seen a unit where the RF and oscillator was tuned but the convertor was not. I have seen AA5s with 3 section tuning caps but never saw an AA6 with a 2 section cap and the convertor input not tuned.
The one thing is that when you get this working, you (and I) will have learned a lot.
This radio has a tuned RF stage, but the Convertor is not tuned. Only the local oscillator is.
From what you describe, there may be an issue with the RF, but I think that the bigger possibility is the oscillator. It may be that your generator provided the frequency that heterodyned with the station that you picked up. If the station was loud, the RF Amp may be good.
If you get a strong station and change the SG freq what happens? I wander if U got the strong station due to a beat freq from that station's freq vs the SG Freq. Do this again with the modulator off. Is the frequency of the station read out correctly on the Radio's dial when the station is received under this condition?
Ordinarily, I would say to touch a long wire to the signal grid of the 12SA7 but since the stage is not tuned, that may not tell you anything.
How accurate is the SG? Check against a known station on a good radio, loose coupled to that radio's antenna.
Connect via a capacitor to the 12SA7 side of C5, set for 455 KHZ and rock the SG dial till you get a loud tone from the SG's modulator. That should tell you what the IF Freq is.
Either your IF is off, your local oscillator is off, or the local oscillator is dead.
Take a transistor radio, tune to a station about 455KHz above a known good station, turn the chassis upside down and hold the radio near the oscillator coil. Tune the CoRadio to the known good station and rock the tuner around that frequency. The other radio should squeal or get quiet when the known station is tuned. If there is no response from the test radio, the oscillator is bad.
If you get the squeal but at the wrong freq, you could try the trimmer on the oscillator section of the tuner cap. mark the current location and rock the trimmer. If no improvement, return to the marked position.
said earlier in this thread that there was little difference between the various AA6 sets. This is me eating my words, as I have never seen a unit where the RF and oscillator was tuned but the convertor was not. I have seen AA5s with 3 section tuning caps but never saw an AA6 with a 2 section cap and the convertor input not tuned.
The one thing is that when you get this working, you (and I) will have learned a lot.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
MrFixr55
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
