03-02-2017, 05:56 PM
That IF valve might have been a variable mu valve, increasing the cathode voltage increases the grid bias voltage thus reducing the gain, manual gain controls were used quite often in comm's receivers as were calibrators which were usually xtal controlled for accuracy and stability, the harmonics of those could be tuned in through all the bands, quite often the tuning scale was moveable by a small amount so that it could be aligned exactly to a harmonic of the marker frequency, check out the Murphy B40d receiver for an example of that.
Lawrence.
Lawrence.
