Building a Power Supply for a 1920's Radio: Page 2

Updated 8/8/05

Retro Electronics Home Page


First of all, we needed to find a power transformer that would provide approximately the correct voltages. We found a unit that would supply 150 volts and 6.3 volts. Here is a picture of the transformer mounted to the chassis:

We set up separate rectifier circuits for the A and B supplies. The A supply uses a bridge rectifier and filter capacitor bank consisting of 1, 2200 mfd. and 2, 6800 mfd. capacitors. This large amount of capacitance is needed to control AC hum, because any hum introduced in the filament supply of the 01A tubes is amplified by the tubes, as they have no separate cathode as most modern tubes do...the cathode circuit connects to the filament.

The B supply uses a single diode and a filter consisting of 2, 100 mfd. 250 volt caps, and a 1000 ohm resistor. After the second cap, a series resistor of around 1500 ohms is used. After this resistor, a shunt resistor is used. This resistor regulates the open-circuit voltage to no more than 120 volts. With the load applied from the radio, the B voltage is 98 volts. A 3.5 meg pot is also connected from the output of the B supply to provide an adjustment for the 22.5 volt supply.

Here is a picture of more progress being made on the power supply's construction.

Indicator lights are used to indicate power supply status: The yellow light is for 110 volts AC, the green light for 90 volts DC, and the red light for 6 volts AC.

This is the test setup with the Arborphone. We needed to determine the correct values of power supply resistors to arrive at the correct voltages. 

Completed power supply.

Here is the power supply powering the Arborphone and the RCA Radiola speaker.

Update 8/8/05: We will be redesigning the power supply to be electronically regulated to provide better voltage control and less heat.


Return to page 1 of the 1920's radio power supply.

Special Features Page

Return to Retro Electronics home page.