SCR-610 Project

Radio Telephone and Telegraph Transmitting and Receiving Equipment
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SGM (ret)
G-Sergeant Major
G-Sergeant Major
Posts: 175
Joined: Mon Dec 20, 2021 5:47 am
Location: Lower Pineland, South Carolina

SCR-610 Project

Post by SGM (ret) » Sun Jan 02, 2022 12:21 pm

My wife and sister-in-law conspired to give me a BC-659 for an early Christmas present. (My SIL buys and sells estate and flea-market stuff as a side business...). I've been collecting militaria since the early '80s, so they both know I have an interest in this sort of stuff.

As with so many collecting projects, it's easy to fall down the ol' rabbit hole, and this one has been no different. After I got the R/T unit, I immediately began looking for all of the missing bits and pieces to build a nice display around it. I started off with finding and downloading copies of TM 11-615 (1942 and 1945) to learn something about the radio and the various components. Armed with a little knowledge, I started looking and planning...

With some research, this turns out to be a BC-659 that underwent depot servicing and modifications at the Lexington Signal Depot (L.S.D) for the Military Assistance Program (MAP). There's a comprehensive stencil list of the MWO's performed on the top of the cabinet. Inside, the paper MFP label has a 1944 date, so I assume that's the original build date. The radio is missing the BA-41 battery and one of the FT-243 crystals, but aside from those bits, it appears essentially un-used. A close examination reveals that someone removed the AN-29 antenna brackets and straps as well as the cable retention straps from the front. I believe this to have been done by someone after the LSD-MAP-MWO refurb since the MFP lacquer on the internal nuts holding these parts has flaked off, but all the other through nuts and bolts are still MFP sealed. (Fortunately, whoever did this retained all of the original nuts, bolts and lock washers!)

The first thing I found to add was an PE-117 power supply. Advertised by the seller as having been restored but not functioning, once I got it in hand, it turns out that it has the PE-120 internals but the restorer replaced with data plate with one for the FT-117. No harm, no foul as I wasn't looking for a functioning power supply, and the resto work was attractive and well done. (The internal parts have been modified with a few, modern solid-state components to provide some sort of 6V input to an unknown output, but those mods are not visible. I suppose it's possible that it could be used or repaired to power the radio. Still, beyond my portfolio.)

Next I replaced the post-war Military Assistance Program (MAP) depot updated latches (the double coil spring type) on the cabinet with more correct wartime latches (spring wire loop type) that I got from a Gee member here. (Thanks, Frenchman!).

With the radio starting to look pretty good, I turned my attention to traying to "animate" it. I wanted to be able to play some audio (wartime tactical radio chatter) over the set's internal speaker, but I also didn't want to have to make any permanent changes or modifications to it. One of the challenges was to figure out how to use one of the knobs to switch the audio on and off.

In the end, I used an MP3 player kit that has an internal 4MB memory and the ability to also use a micro-SD card (aka a "TF" card). I had originally planned to use the radio speaker (3W 3ohm SW-1), but it turned out to be just easier to switch the MP3 player kit speaker (2W 8ohm) with the radio speaker rather than try do the conversion wiring to match the wattage and ohms. I unbolted the radio speaker and was able to simply move it out of the way without needing to unsolder or disconnect its wires. The MP3 speaker was modified to give it a square mount with the correct mounting bolt spacing.

After some testing and experimentation, I also found that the MP3 speaker amp could also drive the meter on the front panel of the radio in synch with the audio. The MP3 speaker is wired in parallel with the LS-171 meter which had its radio leads disconnected (retained by 5/16" nuts).

Finally, the MP3 player's momentary on-off switch was replaced with a rotary switch mounted on the shaft of the radio's channel A-B switch. I drew up a quick CAD sketch of a two-part rotary switch and 3D printed it. I then added terminals cut from 0.005" brass shim stock. The new switch was hot-glued to the channel A-B switch shaft. The speaker and switch wires for the MP3 player were extended to allow me to fit the player into the radio without needing to compromise any more of the original internals. I put the MP3 player controller board and battery box in a vinyl soap box which is held in place with rubber bands.

Everything remains totally reversible - Just unbolt the MP3 speaker and the wires to the meter. Peal the switch parts off the channel switch shaft. Reconnect the meter leads (bolt on) and re-bolt the original speaker back in place and everything's back in its original place.

The audio is turned on by switching the channel selector from A to B. It plays automatically and turns itself off when done. While the audio is playing, the meter oscillates from about 1-1/2 to 2. (In the operate mode on the radio, when the handset is triggered to send, the meter should read at 2, so I don't believe that I'm in danger of damaging the original meter.) My little mod to the meter is not exactly prototypical since the meter actually operates when transmitting and not receiving, but the "animation" is an attention getter. (To be most correct, when I get a correct handset, the phone plug should be left uninserted since the handset phone plug cuts off the internal speaker when it's inserted into its jack.)

I do have an AN-29 antenna on the way, and, hopefully, I have a line on the missing storage brackets and webbing straps.

More to follow as I make progress on building a static SCR-610 radio display.
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