The Mississippi Historical Radio and Broadcasting Society

Vol 4 #3 July 6, 1994

News Letter

Our regular club meeting was held on June 12, 1994. Our next meeting will be July 10, 1994 at 3:00PM. See you there!
Bill Gerk is still working on a "mini-show" to be held down in the Hattiesburg area later this summer. Planned so far is a mini-museum and swap meet. If you have any suggestions - Bill is still waiting to hear from the masses chomping at the bit to help -- so call Bill at 268-6059.
The "Radio in Uniform" project is coming right along -- the list of things needed is shrinking pretty fast! Here is what is still on the list:
Farrar has delivered the vehicle stand - it only needs some final assembly and paint. The holes to mount the casters need to be drilled and tapped in the bottom - and the holes to mount the shock-mounts need to be drilled and tapped in the top - we still need to fabricate the top mounting plate that goes between the shock-mounts and the radio itself. (Hint- Hint!).
The Antenna mount / insulator came in - as usual George (Fair Radio Sales) saw to it that we got a dandy! Brand new in the box from Crosley!

As noted last month - we are looking for people who used some of this equipment in WWII (and / or Korea). We have located an Airman who flew B17 and B19's and is familiar with the BC-348. We hope to talk with him later this month.
Speaking of BC-348's - the prices on these radios is sky-rocketing. Hopefully one of the reasons is because of all of the attention everything WWII is getting right now - hopefully prices will come back to reasonable (affordable) pretty soon -- where BC-348's were going for $75 to $125 a year ago -- we are seeing them from $200 to $350 (each!) right now!!!
One other thing that is pushing up prices on aircraft radios is a surge in restorations going on right now - Sam Heavener just donated a BC-348 to the Smithsonian for the restoration project they have going - THE Enola Gay (that' s the plane that dropped the 1st A-bomb). Several other similar projects are on-going as well and they are throwing some serious money at the electronics.

The BC-348 was designed in 1943 for use in Army aircraft. They stayed in production from 1945 through 1957. We haven't been able to document production in 1944 - though it appears likely. The 348 (and it's jeep cousin the BC-224 which is a 14 Volt version) were manufactured with four major goals in mind: Stability both mechanically and electrically; Selectivity and tuning Accuracy; and high sensitivity. The first goal, stability was achieved by using a (then) new approach to chassis design: a cast aluminum chassis. This allowed for a light yet extremely rigid mechanical assembly that could withstand tons of vibration, all kinds of angles and dangles, and heat / cooling without any tolerances being exceeded. Also adding to both it's stability and the accuracy / selectivity goal is it's super large - high gear ratio drive tuning capacitor. With very large well spaced plates, four sections, and a 200:1 tuning ration. 200 turns of the tuning knob to one turn of the tuning capacitor - and since the tuning capacitor only rotates 180 degrees: it takes 100 turns to tune "lock - to - lock". However, for linearity sake, each band is centered on the "middle" 160 degrees - so it takes about 90 turns to tune one of the 5 bands. The bands cover 200 - 500KC, 1.5 - 3.5Mhz; 3.5 - 6.0Mhz; 6.0 - 13.5Mhz; and 13.5 - 18Mhz. (Yup, no coverage of Standard Broadcast - and I, for one, would love to know WHY??!!). Anyway - a hundred turns of the dial to cover 300KC means each turn only covers about 3.4Khz on the lowest band (less at the low end a little more on the high end). Even on the highest band a single turn still only covers 34Khz. With that high of a tuning ratio and anti-backlash gears - it is rock stable. As noted above, 4 sections of tuning capacitor - the fourth is for the first RF amp. Sensitivity is rated at s+n/n>10db at 5 microvolts: they usually tune up more like s=n/n > 10db @ 2-3 microvolts. There are several series of BC-348 interestingly they seem to run in two types - the "with's" and the "without's". The with / without refers to an extra circuit in one type that employs an Neon bulb as a voltage regulator for the B+ to the local oscillator. The series run something like this:
The Withs:
BC-348 (E,H,K,L) & BC-224 (F,K)
BC-348 (R) (essentially identical to the above sets except for the antenna input circuit).
BC-348 (M,O,P)
(I don't know what the difference is between the E,K,L,R and the M,O,P's are...)

The withouts:
BC-348 (J, N, Q)
In theory, a regulated B+ for the local oscillator should make it more stable - but I've had both types and both are really stable! Warm up a set for about an hour then tune in WWV. Leave the radio alone for a couple of days and come back and find it's still dead on WWV!
The BC-348 was powered by a dynamotor (DM-28) which generated around 220 to 240 volts. The BC-224 used a DM-24. You might think that by putting a DM-24 in the 348 you could run it off of 12-14 volts - but not quite... the filaments are wired different in the BC-348 and the BC-224: The 348 has two sets of four tubes in series; while the 224 has 4 sets of two tubes in series. The value of the limiting resistor in series with the dial lamps is different as well. Most BC-348's (&224's) have been converted to AC. Fair Radio USED to have a transformer known as the Fair 818. It was ideal... the right voltages, plenty of current capacity, not expensive, and it was light. Most people pull the dynamotor off of it's sub-chassis, and mount the transformer and a filter capacitor in it's place. Add some diodes; a little re-wiring and Wow what a nice receiver! If you want to design your own power supply, the DC requirements are: BC-348: 230VDC at .04A. & 24VDC@.95 A.; BC-224: 230VDC at .04A. & 12.6VDC @ 1.55A
The BC-348's served aboard B17, B19, B24 and B26 Aircraft, and probably a lot more. We have footage of a BC-348 in a B17 in use. The plane belongs to the Confederate Air Force. If anyone has more information about the 348 / 224 - please don't hesitate to share it with us!


As a reminder: We are still trying to find radio operators who used military radios during WWII and/or Korea. If you know of anyone, please get us their names and contact information so we can get in touch with them.

Until next time!
Happy Collecting!

The Mississippi Historical Radio and Broadcasting Society Newsletter is published monthly by:
The Mississippi Historical Radio and Broadcasting Society
2412 C Street
Meridian, MS 39301
601 693-5958

© 1994, The Mississippi Historical Radio and Broadcasting Society.

Back to Archive Page