BC-348-P repair and restoration (2015)

Kihwal Lee, K9SUL

This particular unit (ser# 3492) was produced in 1943 by Stromberg-Carlson as part of the 1942 contract, 2542-WF-42. In addition to the shortwave bands covering 1.5MHz to 18MHz, it is capable of receiving 200kHz to 500kHz. BMI and CMI beacons were heard on this reciver. It was mainly used on the B17 bombers and later on the B29.

[Front panel before and after restoration]

The cast aluminum body has a date stamp of Aug 28 1943.

A new AC power supply and an audio output transformer installed

The original power supply was a 28V DC dynamotor. It is basically a DC motor running an AC generator.

The audio output tube was converted a 6V6 octal tube at some point. I corrected the cathode bias circuit and installed a better output transformer.

The finished look.

A RF signal was injected and measured to indentify other issues.

The HFO wasn't working and it turned out to be due to shorted trim caps. All sections needed to be disassembled.

Each section has a date stamp on it. This shows Sep 18 1943.

An example of shorted trim cap

All four (Ant, RF, DET, OSC) sections needed repairs.

More troubles

Pre-assembled and tested the OSC section. The lamp is a 991 tube, a neon voltage regulator (~65V).

OSC putting out a healthy signal on all bands

A BC-348 shown in a WWII B-17 bomber re-enactment.