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THE AM BULLETIN BOARD => Technical Forum => Topic started by: WU2D on March 15, 2011, 08:20:17 PM

Title: DC-DC Whatsit?
Post by: WU2D on March 15, 2011, 08:20:17 PM
A guy at work gave me a BC-603 receiver he had under his desk?!? Now this receiver is 1944 vintage and was the WBFM gear used late in WW2 after Normandy mostly for armor. It seems to tune from 20 to 28 MC.

It was complete with a nice manual and this strange DC-DC converter that he said was the power supply. I assume that this is some kind of 12V to HV converter and since the BC-603 runs on 12V, I suppose it could be the power supply for a mobile setup. Anybody recognize this?

Mike WU2D

Title: Re: DC-DC Whatsit?
Post by: KA8WTK on March 15, 2011, 09:24:24 PM
IIRC, one the dynamotor supplies for the radio ran on 12 volts. There was also a dynamotor that ran on 24 volts. Both supplied 220 volts for plate power in the receiver. I would guess that the radio could be wired for 12 or 24 volts for the filament string. You would need to look at the TM for the unit.
What you have there may be a 12 to 220 volt inverter.

Title: Re: DC-DC Whatsit?
Post by: K9PNP on March 15, 2011, 10:26:25 PM
Like Bill said, the BC-603 dynamotor supplied 220 VDC @ 80 ma to the receiver.  From looking at your PS, looks like a standard 2-transistor multivibrator DC-DC unit.  From the way the transformer is wired, looks like it puts out 1?5 V @ 360 ma.  Can't read the middle number on the transformer specs and none of my crossferences show that transformer.  Looks like it could be wired to put out 220 V by changing the wire from pin 3 to pin 4 unless there is something not obvious that will not handle this.

Hard to tell if it is a commercial unit or a homebrew one.  If it's homebrewed, somebody did a really good job with the heat sink.  The really fun part is wiring the filaments to operate on 12 V without the DM-34 dynamotor with its original plug.  Of course, if you have the TM with it should not be an issue.

Title: Re: DC-DC Whatsit?
Post by: Opcom on March 15, 2011, 11:38:23 PM
It is homebrew, nice job. The two carbon resistors have been hot. Why not replace them with a couple of 5W sand WW's?

Title: Re: DC-DC Whatsit?
Post by: WBear2GCR on March 17, 2011, 10:28:59 AM

Nice BENDIX transistors...

Probably works fine... :D


Title: Re: DC-DC Whatsit?
Post by: KM1H on March 17, 2011, 01:24:42 PM
It looks like a nice HB 12VDC to several useable output voltages using that GE 380 cps transformer. That will sure cut down on the filter cap requirements.

Title: Re: DC-DC Whatsit?
Post by: WU2D on March 17, 2011, 08:29:56 PM
I looked at the soldering and components and am convinced that it is not homebrew. It is commercial.

Title: Re: DC-DC Whatsit?
Post by: Opcom on March 17, 2011, 10:32:00 PM
The exposed wires made me think otherwise but OK. Did you get it fired up yet?
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