These young men previously built a one-tube radio, but now they want to enjoy loudspeaker volume. So they are putting together a simple one-tube audio amplifier described in the November 1940 issue of Popular Mechanics.

To get that volume, they 90 volts on the plate of the 1Q5GT tube, whereas the radio probably required only 45 volts. The article describes how they can use two 45 volt batteries, one running the receiver, with an additional one added in series to supply the amplifier. The article noted that the amplifier could also be used with a magnetic phonograph pickup, or a carbon button microphone could be used to make a simple PA system. If the microphone was used, a different transformer was required on the input, and there would need to be 4.5 volts in series with the mike.

As the picture shows, Fahnestock clips were used for quickly hooking up to the input, output, and power connections.