[Milsurplus] BC-611 F Data Needed

Tue Apr 21 04:28:05 EDT 2020

Mark,

For voltage and resistance charts you need TM 11-4019, the BC-611 Repair Manual.  I offer a reprint for $18.50 plus shipping.  Domestic shipping is $3.50 for Media Mail or whatever the PriMail Flat Rate Envelope costs.  Plus sales tax if you live in Texas.

I have seen radios (mostly BC-611-F’s)  with R1, C13 and R26 missing.  And the BC-611-A didn’t have them to begin with.  However, I have seen no MWO or Change saying to remove them.  I have always assumed that the removals were probably done by the Greeks or Italians when they got the sets after the Korean War.  No ckue as to why.  I usually reinstall them.

However, without C27 the radio would be dead on receive and have no modulation on transmit.  I would first confirm that someone didn’t just relocate it and if not, reinstall it before proceeding.  

The first check one should make on any BC-611-F is to measure the resistance of the primary and secondary windings in the IF transformers.  This can be done without removing tubes or any other components. With an analog meter such as a Simpson 260, they should measure between 8 and 10 ohms.  I have seen readings of between 18 and about 80 ohms indicating a transformer beginning to fail to one on its last legs.  What is going on is that where the Litz wire conductor comes out of the winding and is soldered to a nearby terminal inside the can, when they were made enough of an expansion loop wasn’t left and thermal cycling over the decades is breaking the individual wire strands.  Probably only one or a few batches will have the problem but I have seen it in both Galvin and ERLA models.  The problem is usually repairable but start to finish it is a 2 to 3 hour job with about an 80% success probability.  The reason that it isn’t 100% is that the way that the transformer is made, there is a high probability of breaking one or both of the wires getting the thing disassembled.  This breakage will occur at about the 45 minute point, after you get the guts out of the can because some of the pieces are stuck together which they were not when new.  My recommendation is to replace it with a First IF can out of an –E or earlier.  You will have to drill at least one hole in the chassis and open the IF can and reroute one or two wires.  As the Greeks and Italians did.  The 2nd IF can be replaced by an early 2nd IF can but you must first disassemble it and do some modifications.  But an early 2nd IF won’t work in the 1st IF position.  The early 2nd IF has only the primary tuned.  Which is unfortunate because I have several hundred NOSB 2nd IF’s but no NOSB 1st IF’s,

Anyway, maybe you’ll be lucky and find that all four IF’s are OK.

Robert Downs

From: milsurplus-bounces at mailman.qth.net [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Mark K3MSB
Sent: Monday, April 20, 2020 19:37
To: ARC5; List Milsurplus; Military Radio Collectors Association (mrca at mailman.qth.net)
Subject: [Milsurplus] BC-611 F Data Needed

Good Evening All --

Since I'm working at home I had to move my software development gear from my office into the shack, making things a bit tight.    I put off continuing work on the TBW-HF until some room frees up.

In the interim (after fixing my friends HW-16/HG-10B) I decided to look at my pair of BC-611F radios.  Both radios look great on the inside (anti fungus coating is a wonderful thing.....) and outside.   I had a minor PTT switch issue on one, but I think that's fixed.     Prior to power it up I wanted to do some basic resistance checks but discovered there is no resistance table in the manual TM11-235.   Might anyone have one?

Comparing the two "innards" I quickly discovered one of the boards had some missing components:   C27, R26,C13, and R1.   Since C27 connects V4 and V5 I'm a bit worried.   However, looking at the board,  it looks as if these components were never there in the first place.  There is no evidence that they were removed.

I'm sure there were changes to the 611-F through it's lifetime.   I have TM11-235 May 1945.   I wonder if any of you have a different version out there and could send me the schematics page (which is figure 55 in my manual -- the one from BAMA).?

Even the board that has all the parts is giving me some strange resistance readings.

73 Mark K3MSB

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