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Old 12-30-2017, 08:56 PM
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Winky Dink Winky Dink is offline
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Location: Meridian, Idaho.
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RF Gain Issue!

The restoration was fairly easy. Two of the modules were already gone, and other than deciphering what the last guy had done, it was just a matter of putting in terminal strips to replace the modules.



I have a few TRFs. This is different from anything I've experienced. However, beyond the unwanted reception, the issue is inability to control the RF gain. The original pot was defective, so I tried several others with different resistances and tapers to no avail. The outcome is represented by the blue line.



The red line is what I got after restoring the original pot--removing bumps and adding graphite to the resistive element, resulting in a roughly linear 95K. The original spec was 75K with a fixed 100 ohms at the high end.



I have found one workable configuration--connecting the 40-foot indoor antenna and lowering the line voltage to 80VAC. I know that can be done. You guys showed how to do it when I was doing an AA5 with the wire-wound resistor in the line cord. But assuming I don't want to do that, I'll try your recommendation for separate RF and audio gain controls.

Regarding adding an audio gain control "around the C-7 audio coupler," what kind of potentiometer would you suggest. I have a couple of switched pots with a long-enough shaft to use where the current RF gain control is.

Exactly how would I wire the audio control--where to connect the high, low, and sweep terminals?

In case it's helpful, here's the voltage and resistance data I've collected.



Many Thanks,
Henry
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