[Milsurplus] BC-611 F Data Needed

Tue Apr 21 12:46:49 EDT 2020

Hello (again) Robert.

Thanks for the info.    Yes, C27 is there on the opposite side of the board.

I will be performing resistance checks on the tubes and the IF (hopefully
tonight).

I have to admit,  I was (more than) a bit daunted when I looked at the
board.  Lotsa really small stuff in there.....  we'll see how it goes.

Mark K3MSB

On Tue, Apr 21, 2020 at 4:28 AM Robert Downs <wa5cab at cs.com> wrote:

> 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 2
> nd 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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