The BC-312 receiver serial nr. 13922 CRV, by Michael de Jong PD7MDJ --> I'm kindly asking readers who can provide more information or who can answer some of the questions I have about this receiver to please contact me at polaris@worldmail.nl.
The BC-312 is a U.S. Army Signal Corps HF-communications receiver from the WWII era. It covers 1.5 to 18 MHz in six bands. It can receive AM (voice) and CW (Morse code) signals (for the latter it has a BFO, which nowadays can also be used to receive SSB signals). The BC-312 was designed at the Signal Corps Laboratories in Fort Monmouth, New Jersey in the mid 1930s. It was made by several manufacturers including Farnsworth Radio & Television Corporation and RCA. The receiver was used extensively by the US Army during WWII. It was mainly used in ground vehicles and field installations (due to its high weight it was not or seldomly used in aircraft). It was part for instance of the SCR-299 and SCR-399 mobile communications units (in combination with the Hallicrafters transmitter BC-610), which went ashore early during the Battle of Normandy. The BC-312 has a dynamoter built in and runs off a 12-14V DC power source.
Information on the BC-312 (and the nearly identical 115V AC version, the BC-342) can be found in abundance elsewhere on the internet (see links section below). So I will not be going into detail too much about the history and specifications of the receiver in general; instead this page primarily and particularly deals with the BC-312 that I'm the owner of, a BC-312-M with serial number 13922 CRV, shown in Figure 1. Secondly I've tried with this page to provide a comprehensive list of links to other BC-312 information sources.
It must have been in October or November of 2014 when an unknown, rugged built, and vintage looking receiver caught my eye at the local surplus store. It was lying in the window, and although it's ugly as hell I immediately fell in love with it. Even more so when I started reading about the history of the radio on the internet. It turned out to be a BC-312 of the U.S. Army Signal Corps, quite a legendary WWII radio receiver. Being on a budget, I refrained myself from buying the receiver. Time passed and I tried to get the receiver off my mind. Then I told some friends of the local HAM club about it, and they tried to push me into buying the receiver, as WWII radios in more or less original state (as this one was) are getting harder to find every day. I still managed to keep myself from buying it, and I knew that the longer I'd wait the bigger the chance of succes in bargaining for a lower price with the guy of the surplus store (with the chance of course of the rig eventually being sold to someone else). It was still there late January 2015, and this is when I couldn't resist any longer and I became the new owner of the receiver. With a steel case and a dynamotor in it, the receiver weighs about 30kg. With 200 meters to go from the surplus store to the car, the term "boat anchor" was given new meaning to me, man oh man!
--> Is there a reader who knows what the painted "4" and the red "dot" on the front of the radio means (if the red dot has any meaning at all)?
As mentioned earlier, the receiver is in more or less original state, and at least optically on the outside has not been modified. What immediately did caught my attention was that the engraved lettering is difficult to read. This in contrary to photographs I see of 70+ year old BC-312 radios on the internet that all have clearly visible, white lettering.
In addition, the following parts are missing or modified (see Figure 2):
The Vernier fine-tuning lock mechanism is missing (1).
Above the nozzle, the fuse holder for the fuse of the pilot lamps is missing (2). Below the fast tuning knob there is a spare fuse holder (2). I believe this was originally the pilot lamps fuse holder as there's solder on its connections. Nice detail is that the spare fuse holder still contains an original RCA fuse "Made in Chicago" ("Made in China", I first thought while slowly turning the fuse around).
The covers of the first two phono jacks to the right of the nozzle are missing (3). These two jacks are for a microphone and a key to remotely control a transmitter.
To the right of the volume control, the BFO trimmer (optically like the one below the frequency dial) is missing (4). A black cover is now in its place. Inside the BFO unit a modern trimmer has been soldered in (Figure 11).
Three of the five locking nuts are missing (two of them have been replaced by a normal nut) (5).
The plug of the nozzle normally is a round 14-pin SO-94, for amongst other things connection to a 12-14V DC source and remotely controlling a transmitter. On my BC-312 it was modified into a rectangular 2-pin connector (Figure 9), probably initially to accomodate a 12V source, but which now only has two cut-off, unconnected wires inside the radio.
The name plate (Figure 3) shows serial number 13922 CRV. According to this site CRV means that the receiver is made by RCA. Also other sources mention RCA as the manufacturer of the BC-312-M model. One can also see that the receiver was made for a 1944 contract. --> Is there a reader who can provide me with more information on the serial number and/or contract number? Does a database of serial numbers exist which might help to track down where the unit came from and where it was originally sent to?
Below the nameplate in a triangular configuration three holes are present. I also see these holes on pictures of other BC-312's. I pressume these were used to mount the optional watch holder that's mentioned on this site. --> Is there a reader who can confirm this?
The case of the radio is made from steel (Figure 4). The frontplate of the radio which holds the dials, knobs, and chassis however is made from aluminum. Originally the case had a circuit diagram of the receiver attached to the bottom of the inside, but unfortunately in my BC-312 it's missing. The case originally also had a gasket. The gasket probably got dried out, started crumbling, and was thrown away a long time ago. The top and one of the sides of the case has four holes drilled into them. According to this site this means the receiver has been mounted in a vehicle. The holes were for mounting the extra mount FT-178 (see picture on this site) which prevented excessive horizontal movement. On page 12 of the BC-312 manual (TM 11-850) mount FT-178 is also mentioned. The radio originally was mounted on a FT-162 base mount (shown in Figure 2 above). There was no mount with my BC-312. One of the slides for locking the radio onto the base mount is still there as original part of the bottomside of the case.
Figure 5 shows the inside of the BC-312. Close inspection by me and some of my friends at the local HAM club show some modern modifications mainly to the wiring. It's not unlikely that the radio has been in the possession of an SWL or HAM after it retired from active duty in the army, and that the modifications have been made by this person. Extensive modification or restoration has been made to the BFO-unit. All stages of the receiver are housed in separate aluminum compartments. Most of the compartments look like new inside, but the BFO-compartment is missing its aluminum cover and is a mess (Figure 11). The coils for example look really strange, and I'm not sure if this particular stage is going to be an easy restoration job. The plates of the variable capacitor are not running free either. In Figure 5 on the bottom left you can see the dynamotor DM-21. All of the 9 vacuum tubes are still in place and are of the right type.
A word of caution is in place here: the soldered cans at the edge of the chassis, beside containing three capacitors each, are also filled with highly toxic PCB-oil, this according to various sources. Never open these cans! --> I would like to hear from readers if there are any other toxic or hazardous concerns with this radio that I should know of.
With the dynamotor (Figure 6) the history of my BC-312 takes a strange and surprising turn. The dynamotor has a name plate on it of the French Army (Armée Française) with a 1960 date (Figure 7)!! Also the circuit diagram on the inside of the dynamotor cover is in French. According to this site there was a confirmed production run of the BC-312 in France after the war. One might start thinking that my BC-312 was made in France after the war, but as we've seen earlier, according to the name plate on the front of the receiver it was made by RCA in 1944! Besides, I've seen photos of French BC-312's and they all had French lettering, not English like my BC-312. One theory I have is that my BC-312 was brought to Europe during WWII and after the war was left by the U.S. Army as surplus material to finally be taken over by the French Army. Then in 1960 or later the French Army replaced the broken down original dynamoter with a dynamotor from the French production run. Another possibility is of course that an SWL or HAM replaced the original DM with a French surplus one. The French DM-21 dynamotor in my BC-312 seems to be identical to the DM-21 of the Signal Corps. To make things even more confusing, after completely removing the dynamotor a second name plate was discovered on the dynamotor casing saying that it was made in Chicago (Figure 8)! --> I'm especially interested in hearing from readers about this particular case and the mystery of the dynamotor. After the war, were BC-312's left in France as surplus by the U.S. Army and taken over by the French Army? Does somebody have some more information on the French production run? I hope somebody can shed some light on this.
Caution: the dynamotor turns 12V DC into a dangerous 230V DC to provide high voltage for the vacuum tubes!
So far this report on my BC-312 receiver. I'm in the progress of refurbishing the receiver but I go slowly and step by step. Although I'm a HAM, I'm not a real whizzkid with electronics and taking measurements nor do I have any previous experience with refurbishing vintage radios, but I'm learning every day. So far I've cleaned the receiver both inside and outside. I've used WD40, a LCD/plastic cleaner, a soft brush, and a vacuum cleaner (any cleaning tips will be appreciated). At least mechanically the radio seems to be working fine; the band switch, fast tuning, Vernier tuning, and frequency dials are all working ok. The next step will be disconnecting the dynamotor and trying to power it up. If the motor works, I'll continue from there. I'll keep you posted on my progress with the receiver on this page. How magical it would be if my BC-312 eventually would come alive! The TM 11-850 manual can be found easily on the internet. I also own a printed version of the manual including the circuit diagram. --> If you have any questions or comments, or if you can provide more information on my BC-312, I'd be glad to hear from you on the e-mail address at the top of this page. I would also like to hear from you if you could provide me with the missing parts of the receiver, especially the Vernier lock and a complete BFO unit that's in better condition than the one in my BC-312.
WWII photographs
A BC-312 or BC-342 being operated as part of the SCR-188 radio set by Cpl. John Robbins, 41st Signal, 41st Infantry Division in New Guinea in 1943.
WWII photographs
A BC-312 or BC-342 being operated as part of the SCR-188 radio set by Cpl. John Robbins, 41st Signal, 41st Infantry Division in New Guinea in 1943.
A BC-312 in use by unknown operator.