[MrFixr55]

The basic circuit of the Transitone is very similar all the way into the 1950s. There are 2 basic AVC circuits used in inexpensive AA5 radios:
In one circuit, a separate diode from the detector is used. This is coupled to IF via a 100 pF cap and a resistor. The output of this diode passes through a 2.2 Megohm resistor and filtered by a 0.1uF capacitor to provide a negative DC AVC voltage. One advantage of this circuit is that there is better response from the detector itself with somewhat less distortion. It seems that every Philco that uses a 7A8 or 14A8 uses this circuit, and was used from 1941 - 1952 5 tube AC-DC models.

The other main style of AVC circuit merely takes the AVC signal off the detector circuit at the volume control through a 2.2 megohm resistor. This is literally pulsating DC. The 0.1 uF cap acts as a filter. This is used on most Philcos post 1953.

Both of these circuits provide a negative DC voltage at the capacitor that is used to bias the IF and antenna circuits. The stronger the AVC signal, the more negative the bias, therefore the weaker the gain. The less signal strength, the less negative bias, therefore the stronger the gain.