Thanks for all the thoughtful replies...it's one of the reasons that
this newsgroup is such an outstanding resource.

73
Pete
AC7ZL

Scott W. Harvey wrote:

H. P. Friedrichs wrote:

I cannot seem to get the BFO working, however. The resistors around
the BFO seem to check out ok. The condition of the caps are unknown at
this time, though I have not run across bad silver micas or the pF
dogbones.


Congratulations on getting this far....The BC-348 is a good, classic
military radio and quite a good listener when fully restored.

You need to examine every resistor in the set. Some of them can and will
drift upward in value quite substantially as they age under the best
conditions, and most of these radios were used under conditions that are
far from the best. If any resistor measures more than about 10% off the
marked value, I would replace it.




I know the larger uF caps are prone to dry out and deteriorate, but I
tried shunting a few of them with alligator leads and known-good
units. It didn't seem to make much difference.


Shunting the caps is not a particularly effective troubleshooting
technique because most of these caps are not open, but leaky. Shunting a
good one across a leaky one will have minimal noticeable impact on
performance unless one lead of the original cap is disconnected first.

Come to think of it, you might as well replace all the paper and
electrolytic caps in this radio. Most of them are probably going to be
bad anyway.


What are my options? Is there a common failure mode for the BFO in
this set? Short of removing parts and testing them out-of-circuit what
are my options? Does anyone have a functional BC-348 Q who could give
me nominal voltage readings around the pins of the VT-233 that I could
compare with mine?


I don't have a BC-348 presently, but this site has manuals freely
available for download that will tell you practically everything you
need to know about this radio in almost nauseating detail:

http://www.jamminpower.com/main/bc348.jsp

The files there are huge, but these are the clearest BC-348 manual scans
I have ever seen...Well worth the download.


Side note: The crystal filter also appears not to work. Basically, it
behaves like an open...nothing gets past it, unless bypassed by the
switch. Do these particular crystals tend to deteriorate and die with
age? What do you replace it with, a crystal ground to the IF freq?


You will probably have to get one from a junker BC-348 chassis. IIRC,
the IF frequency of this radio is 910KC, which is somewhat unique.