The AM Forum

"This is 400 lbs of nothing. Actually, it works pretty well but takes
the patience of Job to sort out the millions of tuning units."

CQ Surplus Schematics Handbook, Cowan Publishing 1960

I just came into this beast and it will be quite a project to put it on 75M - What is it?

ahhh a link or an attached picture?...not sure what you are trying to show us.
Fred

I think we are to guess what it is based on those few lines from the CQ Surplus Schematics Handbook.

I got it, it's a BC-653.

Excellent! Nice job OUK.

I guess I'm never going to acquire a taste for military equipment. That thing just looks plain ugly.

Ha! Ugly? That,s nothing - you should hear how it is going to sound with its single tube suppressor modulator and carbonium microphonium. Of course if it should accidently fall on my foot....improved high end.

Good luck in getting it on the air Mike.  Can't wait to hear it and may even have to get up before the sun rises to hear it on the Military net! 

I wonder if that is what you picked up from Steve, WA1HUD?  I was talking to him on our AWA net and he mentioned that you stopped over and lightened his load a bit.   Now you need to help him fix his 183D. 

Cool looking set and make sure you whack the carbon mic on the table a few times before you talk into it! 

73,
Joe, GMS

"Wake Up Little Granules, Wake Up."

Apologies to "Little Susie?"

Yea Rick, you can't spit into em  ;)  Talking nicely to a "carborium microphenoum" will be appreciated!! 

Joe, GMS

I always wanted a BC-653/652 set up, looked at several over the years and today do not know if I would be up to just moving the transmitter around. Good to see you have the 12 volt dynamotors for the radios but understand that they draw over forty amps while in transmit so assuming that the transmitter puts out about twenty watts of A3 with suppressor modulation it’s not the most efficient of radios. I have run suppressor modulated radios before like the Navy TBW and that was capable of good modulation and always had good comments about the quality of the audio. I think the trick to that radio is what set of coils you have for each of the channel sets. There is a mount for the receiver and transmitter so it can be installed in a half track, tank or jeep if you have one and assume that this radio set may be the grandfather of the later GRC-19 (T-195/R-392) 100 watt AM autotune set that was common in the fifties and maybe the last of the military AM sets produced with everything going sideband after that. The more I think about it the more I am wanting one of those sets now, big heavy low power and pointless, want to trade a broadcast transmitter for it? It may weigh about the same.

I have been to the lost city of Petra in southern Jordan and have seen wonders in a dangerous environment with no rules. This all pales in comparison to a visit to the basement of WA1HUD.

WONDERS-WONDERS I SAY!

I dropped off some goodies for Steve of course, but I certainly got some stuff out of there and I think my vehicle was listing slightly as I left. So yes. I filled my quota of replacement small parts (and I had a big list) and I got some heavy metal too for a couple of big projects. BC-191 and BC-653. 

Very nice Mike!

As I mentioned on the ARC-5 reflector over the holidays, my 652/653 is next in line after I get the SCR-274N modulator working (which I opened up last night....).

My 653 came with the 12V dynamotor, but the 652 was dinoless when I got it.  Fortunately I found someone with an NIB 12V dynamotor for it.

Aside from yours and mine, I think there is one operational in the Maryland area (as of a few years ago), and one in Texas.   I know of no others, but I haven't really asked around.

GL OM with Mr. Hernia and his XYL!!

http://www.radiomilitari.com/scr506.html

Here is a nice summary and specs for the system.  Note: Large photo format. You may need to scale out your browser.

Well I will have to be careful on the weight issue but the first order of business was to remove all of the covers and that got her down to below 100 lbs. Sort of manageable. This allowed me to get in and inspect and clean it. Actually I have 2 units. After inspection of both:

Unit 1 BC653A Appears to have all tubes. Has been hammy hamboned with possible VFO messing, and various added wires possibly filament
 mods and all kinds of ceramic discs nailed here and there and a bunch of wires taped to what was the Dynamotor pins. These obviously were how the ham powered and controlled the set. Otherwise complete except for missing pointer knobs and little knurl knobs for the VFOs and Drivers.

Unit 2 BC-653A Appears Original with no mods. No Tubes. But opening the rear compartment by the VFO tuning cap revealed that it had been fractured away with the ceramic Posts broken to get at a coupling of some kind. Obvious human damage.

So the dillema: Do I remove the part from the modified radio to make the stock radio pristine and run it stock?

OR do I leave the stock unit alone and simply hack the hambone radio by figuring out what he did and run it with a power supply.

I may be able to repair the damage but I do see missing parts.

Well, personally I try to run stock as much as possible.    That hammy-hambone mod looks to be pretty ugly.

My unit was missing the "digital" VFO counter.  I have all the pieces from the unit, but they were removed.  The previous owner said a shaft needed replaced.  A picture of my unit is attached.

I'm pretty sure the shaft in the photo is busted, but I haven't yet dug into it.

Well I extricated the loose variable and found out what happened. The variable was completely seized - no turny. I removed it from the unit and soaked the bearings with WD-40. Vice grips on shaft with loving rubber mallet. no turny. Then I hit the shaft with a heat gun and repeated the WD-40 so it really got sucked in and it finally let go. All of the damage was from someone trying to do this and free it while the capacitor was in the unit. They broke the ceramic O collar on the coupler and fractured all three standoffs. The small capacitor at an angle was removed and readjusted. So I think I can repair the assembly if I fabricate the coupler and three standoffs.

The long shaft that you are missing is typically brought out the front to a plate with a dial on it and that looks like the main VFO tuning or driver tuning - not sure. The hamboned unit uses a length of 1/4 inch dowel and a homemade plate.

Restoration work and familiarization continues. The broken ceramic standoffs and ring insulator on the shaft coupling between the VFO and Driver were fabricated at my buddy Spencer's. He has a full CNC shop. We made the parts out of Delran and they fit perfectly and I re-installed the variable and soldered it in. All Fix. I needed to make a couple of plates and some little pointers. one for the VFO main tuning and one which will cover the gaping hole where the Dynamotor goes. This will have a recessed male Jones (I intend on running the beast on an AC supply). That got me thinking about paint. It was pretty rough. With our sudden thaw and high temps, it became possible to talk about touching up the paint. This is crazy to attempt during January but I thinbk I got away with it. Can you say Black Crackle? This required a partial tear down and a lot of taping, a couple of heat lamps and a heat gun and some VHT. But I got lucky and the crink does not look too bad for a novice. There are endless threads on Black Crackle painting and all I can say is you have to do it to really get the experience.

More pics of the BC-653A restoration.

Very Nice Mike!

The "Preset Frequencies IPA Tuning" and similar plates on my unit are somewhat rusty so that will take some work on my unit.

I was tempted to pull out my 653 but stopped myself until the BC-456 is done.  I've learned from past experience that having multiple projects at the same time means typically none get completed........   The replacement caps for the modulator should be here tomorrow, and I have all the connectors I need as well as a spool of era cloth wire.... now all I need is time to work on radios and that's not going to be plentiful for the next few weeks.

I'm planning on using the dynamotor on my 653 but I can see revisiting that plan.  I have a 28V 33A transformer in my pile (which doesn't move very often  ;D) waiting to be put to use.

Well I am about done with the front panel and paint touch up. I still have to move the little thumb knobs for the presets and mount the Jones connector on the Dyno plate I made. I will not paint the sides until Spring. I have to build up a power supply. The VFO false front plate was done up with a cut down velvet vernier and a long shaft and a bracket. It looks OK. Tomorrow I should be able to at least plug in the tubes and see if they light up!

Both units looked like the one with the wires when I started.

Mike

Progress! Filaments Lit Today on TX # 1. Wow those Tungston babies make a light show. There is a rheostat to fine adjust the 814 fils and I will check on the voltage tomorrow. Soon the HV will be applied and we will hope for resuscitation of the beast.

I had one for a while. 2-4Mhz AM grid modulated. The dynamotor unit was missing, ugly, but inside clean. I sold it cheap to someone that wanted to put it on the air. It's one of those channelized sets with LC tuning of the oscillator, and the schematic on the inside.

Here's its page, maybe it will be interesting for some details.
http://bunkerofdoom.com/mil/bc653a/index.html

(Have a look at the BC-640 TX. It's 600 lbs of nothing.. 45W CW and carrier on AM from 100-156Mhz. Be glad you don't have that 7 FT beast.)

Great job on the 653! I'm glad to see one put together and working, and in such nice condition. People used to just strip them for parts.

"This all pales in comparison to a visit to the basement of WA1HUD."

HAH! You haven't seen the basement of the K2PG NJ hacienda, you have to be built like a tree sloth hanging upside down from the 1st floor joists to get around in there. I asked him why he won't get rid of stuff he'll never use like a coaxial trap filter for FM broadcast and he said "I get rid of NOTHING." So, why doesn't he join that PA club known as Pack Rats? Ah, he's a nice guy, I shouldn't pick on him... hoping he doesn't kill me when he reads this. (;->)

Now the Power Supply for the beast. Starting to rough it out. This will have the two matched MOT's (Microwave Oven Transformers) for the 1000 VDC, a smaller transformer for 500 VDC medium voltage and another for the 12 VDC at 10 Amps.  UGHHHHHH! Now you know why this is 400 lbs - of nothing.

The story was that the Generous Electric Company made the beast with a pair of 814s so it would be an awesome CW transmitter. But the Army said - WE WANT AM. So they squeezed a 6F6 on that chassis and a couple of small transformers and suppressor grid modulated it at 1/4 the output power. I suppose this made sense since the likelihood is good that AM would be used for close combat tank to tank to command car or 611 walkie use. And of course the CW would be for longer range liaison.

I see an Electric Radio article in the future.

WA1QHQ

Skip the step of building a power supply.  Graduate directly into a proper Scout Car or other vehicle destined for wartime destruction and use the 653 to order coffee from a drive-through.

 

Check out this working SCR-506 in the Philadelphia area.

http://www.youtube.com/watch?v=Y38rO2tXRjI

Or this one.  http://www.dse.nl/~vrzaob/wc52/radios.html

The bestial BC-653A power supply is finally complete and bench tested under loads. All three supplies appear to be excellent with all kinds of capacity. The outputs are 12 VDC at lots of juice. 500 VDC at significant capacity and an 1110V HV supply made from two MOTs.

I had to play with the HV by boosting the primary with an unused winding on the MV transformer. This trick got me from 975V to 1110. Next I have to make the cable between the PSU and my new Jones connector. The second switch with the red lamp is the HV ON switch which is a step start of about 1 second. Both MV and HV have floating ground (only the 12V is actually grounding); they all see reference to ground at the radio.

You may see the purple wire on the top picture going up to the MV transformer to get a few more volts for the MOT primaries. Both the MV and HV chokes are in the negative lead and the HV has a 25 mA bleed. The MV transformer is one of those cheap but beefy 150 kVA control transformers. It had a 400V and 18V winding on one side and 120V winding on the other. The 12VDC is also based on a an L filter with a homemade choke and 33000 uF and a 150 Ohm Bleed. It is off the four paralleled  5 Amp transformers. The rectifier is off an old ATX power supply; a heat sunk dual Schottky high efficiency rectifier.

My construction practice is adequate, fairly safe but not super pretty. That said, my last really big supply build was for my ART-13 and it is just as good as when I built it in 1993. I also plan on using this supply for the BC-191F project which will be coming sometime this year.

It is ALIVE!

No meter working but on Band C preset I got a strong signal and brought it right down to 80M. The VR tubes lit up and the relay keys nicely. Pop goes the fuse after I started to get some power out. Checking I only had 3A fuses in as a safety precaution. So I went up to 8A fuses and dove in.

How to match this beast? Look at the schematic in the output section. They were trying to load into a 12 ft whip like on a boat! The output network seems to be a parallel tank with a loading coil coming right off the top! This is not going to cut it for 50 Ohms. In a panic move I decided to shotgun in a split C output from the antenna post to a 60pF doorknob to the center of the coax and a 500 pF doorknob to ground. Then I fooled with the loading coil. It is sharp with just one turn up or down effecting the output, but I got 85 honest Watts out into 50 Ohms with the thing. The CW note is pretty good too. Lots to do before I declare victory or try it on suppressor grid AM, but very encouraging since the CW specs say 60 to 90 Watts out depending on the frequency.

While looking at the You Tube video links provide above, I came across this one about the Collings Foundation's B-24J, looks like they have restored the BC-375 and  BC-348 to operating condition.  Check out how they light up a fluorescent tube in front of the row of 211s!


http://www.youtube.com/watch?v=G1S_amgpvVw

Glad to see they have got the old sets running, they have pretty much been static displays only for many years.

AM - not kidding. Last evening some folks gathered at 2200 on 3705 kHz (Sundays) for the low power long range recon net AM version (75M moose and squirrel net ). I had the beast on 3570 on the OMRN CW net (all covers off on floor) doing 90 Watts for its maiden voyage on the air. It has a sweet CW tone. The 807 makes for an "adequate" buffer, for the 814's - that is for sure! By the way - all original tubes. Have not touched or adjusted a thing.

So I tuned one of the preset channels up to 3705 into a dummy load and got 5 Watts out. I had to kill HV and move the tap on the loading coil exactly 2 turns up, readjust the tuning (they call it coupling) cap and bingo 85 Watts. Then I set the transmitter to AM and the carrier dropped to just over 20W. I plugged in a T-17 and by heavens I could hear myself in the receiver. Now this is suppressor grid modulation of a pair of 814's. Flipping to antenna, I yelled for AJ1G, Chris and he came right back.

Still lots to fix and align , but I am getting close to declaring victory.

Do you  mind if I put the schematic on my BC653 web page? Mine is very poor.

Go ahead and stick that schematic on the site. I made it by scanning the schematic from the manual; piecing the two scans together as best I could in Photoshop, and cleaning it up and adjusting the contrast. Not perfect by any means as I just have a small scanner.

There is a faily complete article about this setup in a QST printed during WW2 giving it glowing reviews.  I think it was a 1942 issue which kind of surprised me as I thought that they wouldn't be printing information to let the enemy know what we were using, but maybe it was common knowledge by then. These seem to be really rare today, at least the transmitter and the accessory pieces.  Maybe because the weight turned off surplus buying hams or maybe they just didn't make too many of them. 

Great to know another one gets on the air 70 years later!