ARC-5's: My introduction to WWII Radio Gear

I didn't expect to play around with military radios, since for years my interests laye with older commercial and homebrew tube gear. This started with a BC-453 that was a part of a "junk donation", culminating in the Fall 2024 Classic Exchange, where I made many good contacts on 40 meters.

The completed transmitter and receiver pair during the Fall 2024 Classic Exchange:

I had been gifted a number of items in a "junk donation", and among those was the BC-453 that was largely intact. I had recalled reading about simple converted military gear and my interest was piqued. It was missing its top cover, and a 9-pin tube socket was added in the back where the dynamotor was mounted. The wiring around that socket was incomplete, and contrary to my first expectations it didn't appear to be part of an onboard power supply.

As-received BC-453-A:

It was obvious the unit had been rewired to some extant by a previous owner. I patiently traced the wiring in my BC-453 vs. the published schematic. It was already rewired for 12.6V filaments in parallel, rather than 24-28V in series. The "flower pot" capacitors were leaky after 80 years. I ordered suitable replacements from AES and mounted them onto terminal strips. Re-stuffing the flower-pots was more effort than interested me at the moment, though I did keep them in a bag should I ever change my mind.

Tracing the wiring:

Now what about the additional 9-pin miniature tube socket? As best as I could tell, they were trying to add a product detector using a 12AB7 converter tube. I didn't have any 12BA7's, and wishing to follow a published schematic, I swapped the 9-pin socket for a 7-pin and rewired it for a 12BE6 converter tube. I was able to find a conversion article, "A Beginner's Receiver" by K6JHJ, in the June 1963 73 Magazine Special Surplus Conversion issue .

Schematic (taken from the aforementioned 73 Magazine article by K6JHJ):

I built a standalone linear power supply for the BC-453, supplying 12.6 VAC for the filaments and 150VDC for the B+. It's a plain-vanilla bridge rectifier with capacitor filter design. All built using parts already in my junk-box. I powered it up and was receiving several aircraft NDB's! (from nearby Banks, OR all the way down to Northern California!)

Initially I used the BC-453 "Q5'er" with the IF on my Hallicrafters S_40B. It definitely worked, but I figured building a standalone converter would be more fun. The S-40B drifted around anyways.

Q5'er with the S-40B and homebrew power supply:

Several months later I got around to building a one-tube converter circuit. I had wasted a lot of time looking at more complicated circuits before I told myself "enough is enough" and built the simplest circuit from the October 1949 issue of QST, based around the 6BE6 crystal-controlled converter.
6BE6 Converter

Converter Schematic from October 1949 QST:

Metal work to prepare the converter chassis and the converter after getting it to work:

The BC-459-A transmitter was purchased at the February 2024 Rickreall swapmeet. It had already been converted to amateur used as a CW transmitter, including an SO-239 jack, 1/4" phone jack for the key, and rewiring. The relays had been removed and the roller inductor was disconnected, since it was re-wired to load into 50 ohms.

BC-459 as-received:

For a power supply I found out that another one piece from the same 'junk donation' was suitable: a homebrew AC-4 power supply meant to power a Drake TR-4. It supplies 650VDC for the plate, 250V usable for the oscillator tube, and 12.6V for the filaments. Surprising how things can work out at times.

I built a plate current meter to go in series with the B+ into a little meter housing with black crinkle-paint to matched the BC-459-A. (Surplus Gizmos had that on hand!) Since the AC-4 supply has a remote power switch I also added a power switch.

Plate meter:

Well, that completed this particularly part of the radio journey! I was able to get it all on the air in time for the Classic Exchange and had a great time!