10-23-2021, 10:04 AM
Hi Greg,
Yes, Like Phlogiston, I have seen these. The 8 and 4 uF caps are the Power Supply filters. The 25 uF cap bypasses the 2A5 cathode bias resistor. These points are all positive with reference to B- (chassis ground on this radio). The volume control is interesting but is common among late 20s / early 30s non-AVC radios. The wiper is grounded. one leg of the control goes to the antenna connection. The other leg is part of a variable "voltage divider" that controls screen voltage on the Convertor and cathode bias on the IF Amp. As the control is turned CCW, the antenna circuit is shunted, the bias for the IF amp is increased and the screen voltage is dropped, all lowering the gain of these stages. Turn the control CW, the exact opposite happens. In some radios of this vintage, a more standard AF Input volume control will be ganged with this one.
Yes, Like Phlogiston, I have seen these. The 8 and 4 uF caps are the Power Supply filters. The 25 uF cap bypasses the 2A5 cathode bias resistor. These points are all positive with reference to B- (chassis ground on this radio). The volume control is interesting but is common among late 20s / early 30s non-AVC radios. The wiper is grounded. one leg of the control goes to the antenna connection. The other leg is part of a variable "voltage divider" that controls screen voltage on the Convertor and cathode bias on the IF Amp. As the control is turned CCW, the antenna circuit is shunted, the bias for the IF amp is increased and the screen voltage is dropped, all lowering the gain of these stages. Turn the control CW, the exact opposite happens. In some radios of this vintage, a more standard AF Input volume control will be ganged with this one.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
MrFixr55
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
