[MRCA] Working on an old BC-342

Wed Feb 19 17:33:25 EST 2025

Hi folks

I am on the last leg of overhauling my rather beat up BC-342. It will 
never get into a museum, but it still looks cool and my plan is to have 
it work well so my grandkids can tune around and hear short wave stuff 
with it. (They are 8 and 6 now, so an old WW2 receiver might look cool 
to them in a few years.)  I had a few comments about how to re pack the 
sealed can capacitors in the receiver.  It has about six cans that are 
rectangular and about 1/2" X 1 3/4" and maybe an inch high, with three 
oil filled caps inside. The tops are soldered on and I tried using a big 
Hexacon 200 watt soldering iron.  I would feel comfortable branding a 
rhinoceros with it. It is that big!   It did not take very long with 
some heat to loosen one end of the cap cover and then I could pry it 
off  while applying heat to the can. I started with the three cans next 
to the RF amps. I pulled off three covers in about 2 minutes with the 
iron. A small amount of oil bubbled out, but it was rather easy to 
accomplish with the big iron. I wore nitrile gloves and pulled out the 
guts with a long nose pliers and threw them in the trash. A little 
cleanup with paper towels to soak up any remaining oil, and I soldered 
three 0.05 caps back in the cans so I can seal them up again.   The 
covers got bent slightly while removing them, but they straighten out 
quite easily.  There is a bathtub cap inside the rx as well.  I cut them 
open with a milling machine  on the side that is hidden from view.   I 
am so glad that the soldering iron worked well on those rectangular 
metal cans.

I guess the secret is to use  a BIG soldering iron.  The nice part was 
that I left the cans in the receiver while doing this so it was quite 
easy and painless.  While playing with the receiver, i saw that it was 
very prone to oscillator drift as line voltage changed. A fluctuation of 
less than a volt made the oscillator move and become annoying for SSB 
reception. There is no B+ regulation for the oscillator or the BFO. I 
figured that maybe I could stuff a small solid state series regulator 
somewhere inside. I can probably make one as small as an OA2 with a FET 
and a few parts.    Onward and upward!

73

Dave K1WHS

On 2/17/2025 1:50 PM, J Mcvey wrote:
> Oh you have the "tubs"!  Take it outside, drill a hole in the bottom 
> plate. Hold it With a pair of tongs, heat the bottom over a metal can 
> with a torch. The oil will leak out,  but may flare if you over heat 
> it..The drilling is optional, but maybe a little safer.
> Apply heat around the edges and the solder will  liquefy and drip off. 
> once the solder has dripped off, rap the tub against a fireproof solid 
> surface. The bottom cap will usually fall out. Occasionally you may 
> have to pry it off while heating. Gut it, etc, etc.
> I think it would be a very slow process trying to unsolder that cover 
> with even a BIG iron.
>
>
> On Monday, February 17, 2025 at 01:21:47 PM EST, David Olean 
> <k1whs at metrocast.net> wrote:
>
>
> 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
>
>
>
>
>
> On 2/16/2025 9:05 PM, J Mcvey wrote:
> That's a whole lotta extra work. But if you MUST:
>
> Try carefully cutting the insulator face as close to the metal body as 
> possible, and pry it off , cut the internal wire and remove it , Scoop 
> ior drill the capacitor out. Stuff with a metal film type that should 
> be small enough to fit.
>
> Plan B: Cut in half with a pipe cutter.and remove innards , stuff it, 
> solder the two halves back together.
> One of those two ways will probably get it done, whichever seems the 
> path of least resistance.
>
>
>
> On Sunday, February 16, 2025 at 02:23:20 PM EST, David Olean 
> <k1whs at metrocast.net> <mailto:k1whs at metrocast.net> wrote:
>
>
> About 2 or 3 years ago I bought a slightly re worked BC-342 at Gilbert,
> PA and just got around to trying it out. Lo and behold, it actually
> worked. On closer inspection I found that it had issues. The cursor in
> the frequency window was made from a chunk of #12 copper house wiring!
> I forget who sold it, but the price was right and I figured it would be
> fun to get it going. I read two nice articles about the BC-312/342. Mine
> has the RA-20 AC supply and it had sensitivity at about 2.5 microvolts
> for maybe 10 or 15 dB S/N ratio. According to data that i saw, it was a
> bit deaf. It also overloaded and the oscillator pulled on strong
> signals. I figured that the AVC was probably messed up. I then read that
> there were a few Micamold paper caps inside the RF coil compartments.
> Getting them out of the RX is a chore requiring some serious un
> soldering, but I bit the bullet and started on a re build.  Yes there
> were Micamolds in the RF compartments, but when I looked in the IF cans
> I found 0.01 MFD mica caps that had absolutely no leakage.  The article
> that I read in Electric Radio mentioned paper caps in the IF cans too. I
> did not see that and left the mica caps in there. So I have been
> swapping out the paper caps in the LO and all of the RF and the 1st
> detector stages. Each and every paper cap was quite leaky, so I am glad
> I dug into it. That leaves the metal encased bypass caps left to deal
> with. My plan is to use a big (I mean BIG) soldering iron and gently pry
> off the tops of each can and then dig out the guts, replace with new
> mylar caps and then re seal the cans. I read that someone tried to open
> them with a gas torch and almost burned down his house as the oil caught
> fire.  If I can't pry open the caps, I need a Plan B. Is there a good
> way to replace those metal can caps and still have it look sorta original?
>
> 73
>
> Dave K1WHS
>
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