[R-390] Re: recent experiences (slightly OT)

Fri May 25 19:10:24 EDT 2007

 IMHO, I think the R390 is far superior to most. Both of you had written
about enjoying different radios. I too have some favorite " other" radios.
Although not really a boatanchor, it is on its way, I have an old Yaesu
FRG-7 that I have had tons of fun with. I used to hook it up to a gel-cell
and take it camping. I think it draws 200ma with the lights off. Besides 
that,
I had bought a HH Scott RBO but have not had the chance to use it as it
was destroyed by Fedex. Thinking of that, does anybody have a dial cover
for an RBO. I sure would be grateful.

 Scott

Dan Merz wrote:
> Hi,  my first  complete military radio was a 348P Stromberg Carlson that I
> bought at a garage sale around 1994 for a few bucks.  It had been converted
> to use with an external pwr supply and I used it with a National doghouse
> and was impressed with its performance after I replaced the umpteen  black
> caps that were very leaky in most cases.  I later found a dynamotor and
> restored it to its original configuration.  I can't say it performed better
> after the restoration,  as the dynamotor is a little noisy in itself but the
> experience was 90% of the reward.  I still have it but it's mostly a
> "viewing" radio.  Your experience kindled my interest in listening to it
> once again.   I seem to recall that the dynamotor cost me more than the
> radio.  I vaguely recall that there was one version of the BC-348 according
> to a knowledgeable friend that had superior caps and not the black type,
> either the Q or R model but I am unable to find notes on which one it was.
> It's amazing that these radios still show up in the junk category at thrift
> stores. However,  the general population has little knowledge of this kind
> of stuff. My notes,  which include a complete manual, also include reference
> to the biasing/B- ground location and indication that  cathode bias
> resistors were appropriate if B- were attached directly to ground.   Thanks
> for mentioning your experience,  Dan.   
>
> -----Original Message-----
> From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
> On Behalf Of W. Li
> Sent: Thursday, May 24, 2007 8:37 AM
> To: R-390 at mailman.qth.net
> Subject: [R-390] Re: recent experiences (slightly OT)
>
> Things have been a bit slow, so I thought I would share my recent
> experiences with a predecessor to the R390 series: a BC-348.
>
> Many of us cut our teeth on this aircraft command receiver in the 60's, when
> they came onto the market.
> It was an eight tube single conversion set with an IF of 915KC, maybe 50,000
> units manufactured, and installed in B-24's, B-25's, and B-29's. Even the
> Russians had their version.
>
> Articles in CQ and QST at the time only alluded obliquely to a unique
> perculiarity in the power
> supply: that the B-minus was grounded through a choke incorporated in the
> audio output transformer. Most of the conversion schematics for an AC supply
> erroneously showed B-minus directly grounded. As noted by James Moorer, and
> Mike Dinolfo and others, this error led to excessive current drain by the
> audio output tube, and no negative bias voltage to the mixer.
>
> I failed to satisfactorly rehabilitate my first BC-348 in the 60's, and
> since then, have been on the lookout for a second unit. Most were either
> very beat up or heavily modified by multiple previous owners. Imagine my
> surprise to find a cosmetically perfect unit in our local thrift store
> (among household goods!). 
> Wells-Gardner BC348Q, serial number 7541, order 11415-WF-43.
>
> The interior was exceptionally clean, with that nice phenolic odor. 
>
> All the tubes were JAN originals, and had transconductances exceeding specs.
> Upon tracing down the *upgrades* done by its previous owner(s), I found the
> following:
>
> 1_ all the heaters been rewired correctly in parallel and the 5 and 7 ohm
> series dropping resistors removed.
>
> 2_ pins 1 and 5 on SO-104 were soldered together, shorting the output
> transformer secondary.
>
> 3_ the heater string was soldered to the B-minus choke (pin 6) (!)
>
> 4_ all the leads to the 350K audio pot were cut and transferred to another
> pot in the dial light dimmer position
>
> 5_ all the resistors looked brand new, yet their soldered joints to the
> boards were clearly old and wrapped as they were at the factory.
>
> 6_ all the caps were metal-jacketed with styrene ends.
> There were no waxed paper caps or plastic caps anywhere.
>
> 7_ the huge dual oil-filled cap under the chassis showed less than 10uA
> leakage at its rated voltages.
>
> Once all of the above were dismantled and corrected, I fired it up with a
> metered bench supply, and it worked beautifully, drawing just 50mA at 200V.
>
> My conclusion is that this particular unit never worked as designed, and sat
> around for 60 some-years in a depot, or someone's shop.
>
> Compared to our R390's, this piece of history won't compare in performance,
> but it makes a nice addition to one's vintage collection along my ARC-5's.
>
> W. Li
> Mercer Island, WA
>
>
>  
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