05-16-2020, 10:35 AM
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Hi Terry,
The following was posted by Marc, Victoria, Australia, ARF, September 2009. https://www.antiqueradios.com/forums/vie...6&t=174655
If I am looking at the correct circuit this has a 1232 as a pre amp. Its failure would reduce the aerial input. if there is an error in the AGC circuit or a problem on AGC diodes that could be shutting the first tube down, or causing it problems. That also applies in away to 7B7, as it also has AGC applied to it.
Thats rather a messy circuit around the AGC . It would have been better as two.
Marc
Again in that same post radiotechnician says, “Look for an open coil in the antenna or RF stages, or an open contact to the tuning condenser is those stages...”
Without saying it the answers implies that if the RF is shut down, perhaps at 1232, it would effect the oscillator. Is that true? If there is no RF, say a bad antenna coil, could that shut the oscillator down?
A bit of my radio history:
455 Kc runs loudly through the system, IFs can be peaked.
Anything above about 700 Kc goes nowhere.
Your Signal generator work around proved that the oscillator is dead.
Immediately after recap I had a semi-functional oscillator for a very short time. The reception was horrible with a good deal of noise, and then all of that simply went away, no oscillator at all now. I have done extensive voltage checks around the 7J7 tube. Both pins 6, (grid 1, hp) and pin 4, (grid 3, hp) show 0 volts. I measured that with a good quality digital meter to ground, not cathode. The cathode floats 180 ohms above ground. The specifications from the tube book for the 6J8-G tube which is supposed to be the electrical equivalent of 7J7, indicates that G1 should show a negative voltage up to -3. Does not mention G3, which I am calling the oscillator grid.
Could that lack of negative voltage shut the oscillator down?
I have felt that the antenna coil is functional only because when I am injecting signal from the signal generator to peak the IFs, I am connecting at the antenna input, pin #1, coil 5, “loop loading coil,” through the coil to G1, pin 6 of the 1232/7G7 tube. I would assume that if it comes through at that point the coil must be working?
Thanks...
Tom
Hi Terry,
The following was posted by Marc, Victoria, Australia, ARF, September 2009. https://www.antiqueradios.com/forums/vie...6&t=174655
If I am looking at the correct circuit this has a 1232 as a pre amp. Its failure would reduce the aerial input. if there is an error in the AGC circuit or a problem on AGC diodes that could be shutting the first tube down, or causing it problems. That also applies in away to 7B7, as it also has AGC applied to it.
Thats rather a messy circuit around the AGC . It would have been better as two.
Marc
Again in that same post radiotechnician says, “Look for an open coil in the antenna or RF stages, or an open contact to the tuning condenser is those stages...”
Without saying it the answers implies that if the RF is shut down, perhaps at 1232, it would effect the oscillator. Is that true? If there is no RF, say a bad antenna coil, could that shut the oscillator down?
A bit of my radio history:
455 Kc runs loudly through the system, IFs can be peaked.
Anything above about 700 Kc goes nowhere.
Your Signal generator work around proved that the oscillator is dead.
Immediately after recap I had a semi-functional oscillator for a very short time. The reception was horrible with a good deal of noise, and then all of that simply went away, no oscillator at all now. I have done extensive voltage checks around the 7J7 tube. Both pins 6, (grid 1, hp) and pin 4, (grid 3, hp) show 0 volts. I measured that with a good quality digital meter to ground, not cathode. The cathode floats 180 ohms above ground. The specifications from the tube book for the 6J8-G tube which is supposed to be the electrical equivalent of 7J7, indicates that G1 should show a negative voltage up to -3. Does not mention G3, which I am calling the oscillator grid.
Could that lack of negative voltage shut the oscillator down?
I have felt that the antenna coil is functional only because when I am injecting signal from the signal generator to peak the IFs, I am connecting at the antenna input, pin #1, coil 5, “loop loading coil,” through the coil to G1, pin 6 of the 1232/7G7 tube. I would assume that if it comes through at that point the coil must be working?
Thanks...
Tom
