[MRCA] bc-611 stuff

[WA5CAB at cs.com]

Dale,

Roger has a late -F with the thick bottom cover.  Early -F's and -E and 
earlier work OK with the stock Italian inverters (with the brass loop around the B+ 
post.  However, you usually need to "tune" the flat battery contact springs 
in the bottom cover so that both A+ and B+ springs are firmly touching the 
inverter when the cover is fully closed.  That is most likely all that's wrong 
with your -C.

Late -F's and the BC-721 and AMA models do not work with the stock inverters 
for two reasons in the -F's case and one in the other's.  The brass strip 
fouls the flip-up terminal board and can put B+ onto the headphone transformer 
primary.  Solution is to remove the upper part of the loop but leave most of the 
lower half as part of the solution to the second problem.  

Yes, all of the BC-611's, BC-721's and AMA's used the same BA-38 B-battery 
and either BA-37 or FT-501 & D-cells A-battery.  However, the original batteries 
are free to float up and down independently of each other whereas the two 
sides of the inverter are rigidly attached to each other.Push one side down and 
the other side goes with it.  The battery contacts in the thin BC-611 bottom 
cover are leaf springs.  The battery contacts in the bottom covers of the late 
BC-611-F, BC-721 and AMA are rigid posts.  Whichever of A+ or B+ posts touches 
the inverter first pushes it down and the other post never makes contact.  

The best solution I have seen is to remove part of the brass strip, and fit a 
compression spring over the B+ post in the bottom cover.  ID to be a tight 
fit on the post and length about 5/8".  When the cover is closed, the A+ post 
will make contact with the A+ contact on the inverter.  Then the spring will fit 
down around the B+ contact (rivet) and sit on the remainder of the brass 
strip.

The modified inverter may not work with a thin bottom cover.  Depends upon 
whether the B+ leaf spring can be bent up enough.  Solution is to install a 
brass binding head machine screw and about two brass flat washers into the hole in 
the rivet.  Be sure that the OD of the washers is small enough to fit inside 
the compression spring.

As a final fix, make and install a 1/4" spacer against the outside wall of 
the B-battery compartment.  Width and length to fit the compartment.  Trim the 
top (end that goes in first) to clear the B- spring.  Bevel the top so you can 
easily load in the three D-cells.  The spacer eliminates most of the rattle 
when you shake the closed up radio, keeps the D-cells standing up straight, and 
eliminates intermittent operation due to shaking.

In a message dated 1/10/2006 12:59:02 PM Central Standard Time, 
kw1i at earthlink.net writes: 
> Why doesn't the inverter work with the F?  Aren't the original battery 
> packs
> identical?
> 
> My brother and I have BC-611s.  One works with the inverter, one does not.
> The one that works is an F, but the other one that doesn't work is the C
> variant.  They both work with original battery configs.  I think it's a wear
> and tear issue with contacts as well as some small variation in the
> dimensions on the inverters. I have been meaning to tack some tiny wires to
> the internal battery contacts and close the covers to see what is going on.
> 

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)