[Milsurplus] BC-611 case screw and MWO questions

[Mike Morrow]

Robert wrote:

>The original top cover retaining screw is #8-32x7/16 Binding Head Captive
>Machine Screw, Black Oxide finish.  Signal Corps Stock Number 6L6832-7.94S.
No
>lock washer and no flat washer.  The seal was a fiber or neoprene flat
washer
>that fits the counterbore.  I've seen some of the correct screws but with
green
>finish and surmised they were from a depot respray job.  Or maybe post-war
>replacement parts.
>
>BC-611's stayed in service with several NATO nations (Italians and Greeks
at
>least) into the 60's.
>
>MWO SIG 11-235-6 dated 4/1/45 repeated parts of earlier ones, replacing
>bakelite mic and earphone caps with aluminum ones, and installing MC-162
earphone
>cup on earphone cap and M-367 canvas cover on mic cap.
>
>We think that -7 was installation of the ground buss wires alongside the
tube
>sockets and -8 was the installation of a metal clip on the ON/OFF tab on
the
>bottom of the antenna.  This is conjecture based on cases with stamped
MWO's
>and what was found inside.  I've never come across the paper hard copies of
the
>MWO's.

Thanks very much for the info, Robert.  It appears that none of the units
I've run across have the appropriate "official" screw and washer.

My May 1945 TM 11-235 on the page 98 maintenance parts list gives the SC
stock number for the top plate screw as 6L6348-12.5, and the washer as
6L50523, but provides no further description.

I've developed a great repect for the design of the BC-611.  It effectively
implements a five-tube superhet receiver with RF stage and a four-tube 0.25
watt output plate/screen modulated AM transmitter, using an actual total of
just five tubes.  That long multi-section PTT switch made that possible.
The feature of only powering one-half side of the filaments for the 3S4
tubes in receive mode is a nice power-saving feature.  Compare that to the
USN's MAB/DAV units with their simple PTT switching, which used seven tubes
to do about the same thing and still had no receiver RF stage.  It would be
interesting to know more about the history of the BC-611 development.

One still runs across statements that the transmitter power output of of the
BC-611 is only about 35 mW (PA efficiency of about five percent!), but
paragraph 116 (transmitter performance) of  TM 11-235 states that average
unit modulated power output is a much more reasonable value of about 250 mW.

I wish I could find a stateside source of one of those solid-state D cell
BC-611 power packs.

73,
Mike / KK5F