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

[wf2u at starband.net]

Congratulations on the nice BC-348 rescue story.

Indeed these receivers are nice considering the technology. Many of us
military radio collectors are still using them on the ham bands.

I for one, have one paired up with the ART-13 transmitters as in one of
the original aircraft configurations.

To attest to the successful design, the copies of the BC-348 receivers
were manufactured and used in the Soviet Union until the mid-1970's, as
well as those of the ART-13. Except for some more modern passive
components and wiring techniques/materials, the receivers remained
essentially the same as the original BC-348. In the later production
models the Russian BC-348's (their model number for it was US-9) the
dynamotor was replaced with a plug-in equivalent solid-state inverter.


I'm also the lucky owner of such a Russian-made ART-13/BC-348 clone pair.
My receiver has a manufacturing date of June 1966!

This station sits righ next to my ART-13/BC-348 combo.

73, Meir WF2U

> 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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