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Author Topic: Old BC-312M, foregin maded?  (Read 4125 times)
9A5BDP
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Posts: 115




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« on: January 20, 2013, 09:36:54 AM »

Hi there...

I have one piece of the famous BC-312M receiver (SN:520) with some printed notes on the frontpanel:

MWO-II-830-1
MWO-II-830-3
MWO-II-830-4
MWO-II-830-6

Receiver is heavily modified in the part of detector and AF stage and dynamo is also replaced with 230V mains powered PSU.
If any of you guys/girls have some informations on these notes I will be very happy to hear what they mean.
I want to restore as far as possible regarding of replacement parts and function. This receiver in not in operational condition so I will need advices from you for my restorings activities in the future.
Also one thing...did this model of receiver ever build outside of the States? I found information that is in France after WW2 was some manufacturing site..and mine unit have some original parts that is maded in one Yugoslaw factory, I am very curious regarding this possibility that is this receiver maded not in States..

Thanx to all for assistance

73!
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VU2NAN
Member

Posts: 253




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« Reply #1 on: January 20, 2013, 10:10:43 AM »

HI OM Dubravko,

MWO may stand for Maintenance Work Order or Modification Work Order and one wouldn't get any information on that!

Have you checked this out?

http://www.radiomuseum.org/r/military_bc_312_m.html

And this?

http://www.virhistory.com/navy/manuals/94200/94200_1_05-4.pdf

73,

Nandu.

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9A5BDP
Member

Posts: 115




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« Reply #2 on: January 20, 2013, 10:43:36 AM »

Yes, I browse and check yours manuals even before but without any luck. My main question is how this receiver have US army marks and some vital pasive (capacitors) from exYugo factories? I check if these parts are some sort of mod or original and the second is right.
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VU2NAN
Member

Posts: 253




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« Reply #3 on: January 20, 2013, 07:37:34 PM »

Hi OM Dubravko,

The original capacitors are rectangular metal-can, oil-filled and 3-in-1. If not they have been replaced.

73,

Nandu.

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VK3DWZ
Member

Posts: 47




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« Reply #4 on: January 20, 2013, 11:36:57 PM »

Probably made in the U.S., and modified in a foreign country.  I once saw, in the offices of China Radio International (in Beijing), some communications equipment made during World War II.  One piece was a BC342, and the other was an R.C.A. AR-88 with a Chinese front panel.  Goodness knows what else was done to these receivers.
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9A5BDP
Member

Posts: 115




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« Reply #5 on: January 21, 2013, 01:35:58 PM »

I am very confused. All the notes and lettering on the front panel are on english language but interior sudgest that is not meded in USA. Maybe is some sort of join job between two countries at the end of WW2. Tubes are original RCA and Kenrads brand. Mechanicaly is very well build. I am hoping to put some pictures of the interior during this week.
I must rebuild everything from 2nd detector to the speaker. First tube I will put 6R7 and for second one I will put 6V6GT for the availability reasons regarding very obsolete 6F6 tube. Did any of you guys know what is input impedance of the T1 transformer? And some sharp closeup pictures from the T2 transformer will be very usefull for me...

Also I heve some questions regarding PSU:
- it is better to use external PSU or to put everything inside of enclosure?
- how dificult is to obtain DM dynamomotor in USA, because is very hard to find in Croatia, even in Europe?

Thanx in advance 73!
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G3RZP
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Posts: 4842




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« Reply #6 on: January 21, 2013, 01:50:18 PM »

It has probably been heavily modified, which is why there are components not of USA origin. Some US equipment was copied in the Societ Union - one example was the BC221 frequency meter. Not all of them had panels in Cyrrillic characters, though. Your rx was probably US manufactured and possibly overhauled in US Army workshops in Europe.
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9A5BDP
Member

Posts: 115




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« Reply #7 on: January 22, 2013, 01:16:48 PM »

And, most important thing...how is this receiver good for listening DX stations? It is better to use resonant or nonresonant antenna with him?
I am thinking now, maybe it is not heavily modified but on contrary...manufactured with domestic parts with exception of vital parts.


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W9GB
Member

Posts: 2656




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« Reply #8 on: January 22, 2013, 02:11:40 PM »

Quote
Did any of you guys know what is input impedance of the T1 transformer? And some sharp closeup pictures from the T2 transformer will be very usefull for me...
For T2 :
Farnsworth models (Ft. Wayne, IN) had PIN jacks
RCA models (New Jersey) had soldered terminals

BC-321
Type: Communication Receiver (also Amateur)
Manufacturer/Brand:    MILITARY U.S. (different makers for same model)
Year: 1936–1960   
Receiver Range: 1.5 MHz - 18 MHz, IF 470KHz, Crystal filter,
9 tubes: 6C5 6C5 6F6 6K7 6K7 6K7 6K7 6L7 6R7
Power by DM-17 or DM-21,

Schematic
http://www.nj7p.org/millist/sch/bc-312.gif

Picture
http://www.nj7p.org/millist/pic/bc-312.jpg

Rebuilding Bakelite Block Capacitors
http://www.philcorepairbench.com/capbuild.htm

Rebuilding Bathtub Capacitors
http://www.boatanchors.org/filtercap.htm#Bathtubs1

Importance of Line Filter Capacitors in Tube Radios
http://www.justradios.com/safetytips.html
« Last Edit: January 22, 2013, 02:23:37 PM by W9GB » Logged
9A5BDP
Member

Posts: 115




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« Reply #9 on: January 27, 2013, 10:52:06 AM »

OK, thanks for a list of external links. Fine bunch of usefull informations are included it these documents.

I want to know what type is SPST switch for changing receive/transmitt? I found in service manual that is SPST type switch with contacts good for 3 amps and 250V. I have in my junkyard some of that types but unfortunately without round/ball style of handle. Please advice me where to find that kind of switch?

With best regards...

73!

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W9GB
Member

Posts: 2656




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« Reply #10 on: January 29, 2013, 06:06:45 PM »

LEVITON still makes a wide variety of single hole "appliance and machine style" switches.
http://www.leviton.com/OA_HTML/SectionDisplay.jsp?section=41555&minisite=10251
Some of these designs have not changed since 1930s, but using newer materials (plastics instead of Bakelite), like the 720 series.

Measure hole size in panel and required thickness to fit the panel (clearances).
Some switches have "key ways" to fit panel cutouts.

w9gb
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9A5BDP
Member

Posts: 115




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« Reply #11 on: January 30, 2013, 01:26:39 PM »

Yes..this is kind of information that I need, thanx a lot...

Only I must to see do they accept paypal or some of credit cards...

Thanx for infos...

Its now possibile to obtain somewhere neon bulb for input protection (NE...something) type from GE?

73!
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