[Milsurplus] BC-611 case screw and MWO questions

[WA5CAB at cs.com]

Mike,

In a message dated 10/2/2005 11:26:42 AM Central Daylight Time, 
kk5f at earthlink.net writes: 
> >6L6348-12.5 must be a typo.  It would cross to a #3-48 x 1/2
> 
> Yes, it doesn't seem to fit.  But it's what appears in the May 1945 TM
> 11-235.
> 

I don't have it clearly ID'd (at least not years after I wrote it) but that 
part number may be the screw at the top of the chassis that holds the parts 
together for the pivoting crystal clip.

> I'm looking at replacing the dried and compressed gasket materiel on the 
> top
> and bottom plates of  my BC-611-F.  What's there now is black and appears to
> have been laid into the sealing groove as a liquid, rather than as a
> separate appropriately shaped gasket.  What's odd is that the TM references
> these sealing gaskets by separate part number as it there were pre-cut
> gaskets intended as replacements.  Have you (or anyone else on the list) any
> suggestions of a commerically available product that will look and function
> appropriately when dried, and is easy to apply?
> 

Despite what it might look like in your set, the top and bottom cover seals 
were not molded in place.  I once, years ago, had an NOS replacement.  They 
were separate parts molded of two or three different kinds of rubber over the 
course of production.  Ten or twelve years ago, I tracked down a company here in 
Houston who stocked a line of square cross-section O-rings.  I went over there 
with a bottom cover and one of the guys brought several sizes of rings up 
front and one of them when laid into the groove was a perfect fit.  Material is 
70 durometer neoprene.  Over the years, I've sold (or used and then sold or 
used the covers) almost all of them and have been thinking I had better see 
whether the company was still in business and get some more.  Price is $3.50 each.

> Robert, you mentioned in a posting here four years ago that the solid-state
> BC-611 D-cell packs worked OK on every model except the BC-611-F.  What
> keeps that device from working with the BC-611-F?  I'd like to find one of
> these packs someday if it can be made to work with a -F model.
> 

The DC-DC converter made in Italy is made from two dissimilar length tubes 
the same diameter as a D-cell or BA-37.  The two tubes are offset and welded 
(some recent ones appear to have been glued) together.  The original BA-37 (or 
FT-501 and 2xBA-30) and BA-38 weren't tied together and could float up and down 
against the springs independantly of each other.  The 4 D-cells and converter 
all move up and down as a unit.  With the BC-611-A through early BC-611-F you 
can "tune" the flat springs on the battery contact plate in the bottom cover 
such that when you close and latch the cover, the A and B sides are both 
connected.

The thick bottom covers on the late BC-611-F, all BC-721 and M-416 (of IE-17) 
have two solid posts for A and B connections.  When you close and latch these 
covers, whichever of the posts touches first pushes the converter-battery 
assembly away as you complete closing the cover.  And the second post never 
touches.  In addition, when the converters were designed, there must have been an 
error made in the length or position of the B side.  Rather than correcting the 
error, they added a flattened brass strip loop secured by the B contact 
rivet.  This fouls the flip-up mic and earphone contact board in the late F case.  
I've seen several solution attempts, the best of which (in my opinion) is 
removal of part of the brass strip loop, installation of a brass screw and some 
flat washers into the hole in the B contact rivet, and installation of a plated 
steel or phosphor bronze compression spring on the B post in the bottom cover. 
 Enough of the brass strip should be left to provide a landing contact zone 
for the compression spring as it spigots over the contact rivet.  If you don't 
need to use the unit in a thin-bottom cover radio, the screw and washer(s) 
aren't needed.  The ID of the compression spring should be a snug fit on the B 
post.  I forget the length right now but think it was 3/4", maybe a little 
shorter.

73
Robert Downs - Houston
<http://www.wa5cab.com> (Web Store)
MVPA 9480
<wa5cab at cs.com> (Primary email)
<wa5cab at houston.rr.com> (Backup email)