The AM Forum

The BC-640 is a 100-156 MHz, 1 crystal channel, AM, 50 W carrier, 110/220 VAC, Rack mounted transmitter.  About 6 FT and I'm guessing 300-400 lbs after having loaded it piece by piece.

I may be stuck with it unless my collector gets back with me quick, so may as well ask if anyone has a free manual or schematic. I have searched in vain for it.

The BC-640 set is much rarer than 2M AM activity, but the BC-639 matching receiver is much more common. A 50W carrier in 2M is nothing to sneeze at, but at 8 LBS per Watt, it's a beast.

One panel is missing, no idea what it is, but I have these from top to bottom, so it would seem complete. What could be missing??


1.) RF final amp, p-p 24G or 35T's?
2.) RF multiplier and driver
3.) (missing panel-unit)
4.) control unit
5.) modulator
6.) power supply
7.) AC input voltage adjuster (variac and meter)

There above is all the items for an AM set. Looking at the obvious modulator chassis, the low level stages seem to be on that chassis. Mystery as to what is missing.

Notice on the bottom unit, the AC line meter is recessed, at an up-angle for viewing, and is protected by metal bars against accidental damage by people's feet.

The pics sent to me, that convinced me to drive 70 miles round trip to get it,  indicate the many tubes were all present. However, some pest took most of the tubes before I got there.. They left only the VHF RF triodes.

If the book or legible schematics can be found, I can decide if it is complete enough to be worth putting back together. Otherwise it will be for parts.

"Transmitter, rack-mounted, 100-156 MHz, 40 W AM, P/O SCR-562, SCR-573, SCR-643; AN 08-40BC640-2, 1943 "

Anyone who would go thru all the trouble to set that up for just 50 watts of crystal controlled AM on two meters must certainly qualify as some sort of ship, don’t know about tall or not. At MRCA up in Pennsylvania some of us played around with military stuff on 144.250 simplex, SCR-522 and the like but we also had a category for people who bring out the most useless radio. A rule is that it has to be something that works and considering the size and weight of that transmitter it would have been a strong contender for winning that category, although the TBS UHF stuff is hard to beat in level of uselessness. Something along the same line of what you have I have always wanted to do, no good reason just want to get an old GE Progress line base station in the full size six foot rack set that up maybe on 146.52 I remember seeing those old progress line and Master base stations as a kid and thinking they were wonderful radios in how they were built, the old Motorola’s just did not have the same style as the GE stuff.

If my collector friend does not get back with me, It will have to be parted out for lack of space. I have to give him some time because he is in the Army national Guard and whereabouts is unknown, he might be away from communications at this time. He's a Major, so at some point before long, he will come into contact with a terminal and e-mail, due to reports and orders. For now, I only asked him to acknowledge my message. I think I can shove this into the backyard lawnmower shed. At least it does not leak and there do not seem to be mice.

I really want the schematics because I had this same power supply before, not knowing what it was from, and never did figure out where 120V came in. It's an odd setup. I know that sounds weird but it has many, many windings on the main transformer. There is something very unusual about the power supply scheme. The power supply has some 20 stud-and-nut connections along the back, as do the other sections. Plus some ceramics.

The 1960 “CQ Surplus Schematics Handbook” pages 34 and 35. Description and schematics just looked at them and kind of neat the way they use two power supplies, AC power control chassis and one chassis just for a controller. May be the most over designed 50 watt radio anywhere. If you don’t have the book I have it in a PDF and can send it to you. Think you have my direct email.

Just went back and read some more of the book, lot of the Millist people and the like get all worked up about some of the CQ books and there commentary but I love them, the author of the manual refers to the BC-640 in his last paragraph as “This is the biggest, most powerful TVI generator ever built, and with slight modification will be able to completely blank out all VHF and UHF channels for mils around. This gives TVI even when turned off.” Got to love anything described like that!

Seems you are missing the modulator - a nice chassis -full of 6L6 and 811A.....

I have a full manual here, but it is a bit large to email!

Just looked again - you have the modulator...... will have another nose.....

Solved....

You are missing a power unit - I think they are the same for the modulator and the RF section.

Be a shame to part it out, but what else can you do? there are far easier ways of getting 50Watts of AM at 144Mhz!

I was sent a copy of the CQ book with the schematic. Its legible but bare of component values and voltages. The power units seem identical, hard to say without a parts list. The good news, though, missing a power supply is better than missing a modulator.

I'd love to study the complete manual. Can you put it on a webserver temporarily?
It might go though e-mail, hard to say.

Thank you,
Patrick

I will have a look for the relevant disc later on - will see if I can get it online somewhere.

I have a modulator here, that i am planning to use in my HB HF rack - another local Ham here has most of a BC640 (has the same issue as you - missing a power unit), I hope to prise it from his storage, and get it on the air...

Have a look for a T1131 - this is the British version of the BC640 - you can tell it is British, it is pig ugly, and weighs about double a BC640......



Manual can be found here

https://www.dropbox.com/sh/mib4ix2kbm8psmi/H99SkyRlDA

There is a complete unit in nice shape for sale, probably cheap, in Ohio on Ebay along with other nice stuff. I thought I'd put the link here since it's the (old) BC-640 thread...

http://www.ebay.com/itm/WWII-Signal-Corps-BC-640-B-Transmitter-Rack-1943-Ham-Radio-Air-Force-Army-Navy-/161052477558?pt=US_Ham_Radio_Transmitters&hash=item257f79c876

ER 276, May 2012, had a good article on the mating receiver system BC-639 (fixed the typo).

73DG

I think you meant the BC-639, I've got an ex-FAA one around here somewhere. That should find a home...so much stuff, so little time!

That ebay unit sure is pristine looking, I wish I could have it, but Ohio is so far away it's not practical to go get it with the vacation I have saved up. I've alerted my military friend. Maybe he can get someone to pick it up for him.

Or, someone local to the beautiful OH area could agree to get it and hang onto it for me?  -but it's really heavy.

In the time passing, the already-obtained unit is in my garage until August when the Major can come get it an a pile of other stuff I have saved for him. The manual has been good reading.

It is a very straightforward TX despite the half mile of wire inside. All it would take is a swap of tuned circuits, lots of room inside. Honestly the more it sits in my garage the more I think about 2M AM. 40-50W carrier would be gangbusters on 2M. It's very simple with frequency multipliers, etc. so it could be put on any ham band if someone wanted to fiddle with one.

On the BC-639, I know a guy that will give it a good home. -same military guy as collects the transmitters. Power supply is a bonus as well.

Patrick

I have an original BC-639 RX W/PSU, and it is a constant source of air traffic related chatter.

More entertaining than a police scanner.

73DG

The guy is not going to bid on the TX. No space.. It would make someone a fun project.

The eBay offering is really pretty. The design and color scheme. A lot of stuff to make 50 Watts.
But it looks like another one of the Area 51 electronics that you have been posting here, Patrick.....

My EE classes in college used one of those transmitters to teach the various stages of a transmitter and how you tuned one up.  I seem to recall practically everything but the filament temperature being either metered or adjustable, or both.   It used some 3C24's as I remember.  We got a case of them from the Army, all new in box, marked Heinz and Kaufman, and every one of them was a complete dud, zero emission.  TV sets in the vicinity of the college breathed a sigh of relief.

I still have that thing. Found an extra modulator for it, and what might be a set of power supply iron and a power supply front panel (ok so where in the world is the chassis???). It's been moved from the garage to the utility room at least. Figured out it is the -B model, identical except for having one meter instead of five (not including the mains voltage meter on the variac panel). The single meter is used as a multimeter with a switch to select its function. It is probably a late -B model as the early ones had covers over the punched meter-holes and this one has no holes ever punched in the panels.

I have not been able to raise the Major via e-mail in a long time. I hope he is well.

It is attractive to put this on 2M AM, but looking for info led me to this other older topic
http://amfone.net/Amforum/index.php?topic=33419.msg281012#msg281012
in which there does not seem to be consenus about Frequencies, at least in Texas. I am in Dallas and there are many repeaters and VHF folks. The most prominent groups seem to be into FM, such as a VHF-FM Society which is into FM obviously, and the North Texas Microwave Society which is into 220MHz+ and very much into the way-up GHZ stuff and data., etc.

Having the manual I have since figured out that building a replacement power supply is trivial and the front panel will make it appear legitimate. The only "mess" in this transmitter is that created when someone removed all the modules (rack chasis) therefore disconnecting the wiring harness from the terminal strips on the rear aprons of said chasis'. It's likely to sit here for some time because:
1.) The set is 600LBs and to move it the chassis' have to come out to lighten it, very funny since I could have moved this myself 20 years ago.
2.) It's too hot in that room to sit there and try to re-connect. Summer.
3.) It is dark in there. Lights are hot.
4.) Need to make a hole in the shop floor area to put this and work on it where there is test equipment. Easier said than done.

That's the status on this rig anyway. BTW the output is 18x the crystal freq so it is reasonable even for a DDS or regular VFO from 5.5555MHz to 8.6666MHz.