[MRCA] Working on an old BC-342

[David Olean]

Hi Ray

I am changing out all of the caps.  There are about 22 more in those 
metal cans. I can't believe that the set works as well as it does now 
that I fixed the AVC caps.  I am also adding a bit more filtering to 
reduce hum in the B+ line.  I would not trust the old caps for one 
minute!  The good news is that my BC-342N has a 250 ohm tap which might 
work better with headphones.  Currently it is set for 4000 ohms.

Dave K1WHS



On 2/17/2025 3:02 PM, Ray Fantini via MRCA wrote:

> Leaking screen grid capacitors will hurt sensitivity, leaking 
> capacitors in the AVC bus will cause distortion and overloading. Small 
> leaks can make a big difference. Also leaking capacitors can turn into 
> shorted capacitors if you don’t address them.
>
> Remember to pack away a high impedance speaker with the radio, they 
> don’t like being connected to a four ohm speaker.
>
> Ray F/KA3EKH
>
> *From:* mrca-bounces at mailman.qth.net <mrca-bounces at mailman.qth.net> 
> *On Behalf Of *David Olean
> *Sent:* Monday, February 17, 2025 1:22 PM
> *To:* J Mcvey <ac2eu at yahoo.com>; Military Radio Collectors Association 
> <mrca at mailman.qth.net>
> *Subject:* Re: [MRCA] Working on an old BC-342
>
> Hello folks and thanks for the advice on the BC-312/342. The oil 
> filled caps in the BC-342 are rectangular and soldered together.  
> Luckily they are all located in HV  B+ lines and are not in the AVC 
> circuits.  They are working for now in my radio.  I will try the big 
> soldering iron idea first to remove the covers. If that does not work 
> very well, I can saw the cap apart just under the top cover. That will 
> require removing all of the caps though.  Once sawed in two, the top 
> cover can be re installed on the capacitor body and the only 
> difference will be that it is a bit shorter.
>
> I did dis assemble the radio by unsoldering all of the RF coil and the 
> oscillator compartments and swapped out all those Micamolds that were 
> in the AVC line in those boxes. I put the radio back together and the 
> set really took off. As the tubes warmed up, I was greeted by a very 
> ample supply of background noise on all bands.  The set is not hot as 
> a two dollar gun. I checked the 6 dB S/N ratio at 5 MHz and saw 0.26 
> microvolts for a 6 dB jump in audio. A 1 microvolt signal is now loud 
> on all the bands.
>
> My plan is to give the radio to my grandkids and hope they get a kick 
> out of snooping around on the air waves.  At a minimum, it will get 
> some attention.
>
> I also did some snooping around and found a very early article by 
> George Grammer back in Septemer of 1946 on the pages of QST. His 
> article is great and covers many items that need work to improve the 
> radio. Sadly, many subsequent articles are around that have 
> plagiarized the original. Some parts of the texts are copied almost 
> word for word.  Pretty sad. There is never any ref back to George's 
> original work.
>
> 73
>
> Dave K1WHS
>
>
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