[ARC5] BC-348

[Mark K3MSB]

 Several months ago at a hamfest I picked up a rat infested / urinated /
gnawed to death junker BC-348Q (for $5) and I harvested what I could.
Fortunately, all 4 modules were very clean on the inside and not urinated
on or even gnawed.    Yes, I used gloves and a face mask while working on
it.....

There's a 0.05 uF 400V Tubular Capacitor in the OSC compartment.  It is the
Oscillator Unit Screen Bypass Cap (Part 60 -- I think, my schematic is
fuzzy)     I'm not sure what they mean by "tubular" in the manual,  perhaps
one of you can enlighten me.   I've always thought tubular was a shape,
not a type (like mica,  wax paper, etc).

You can see a picture of it here (bottom row):
https://www.k3msb.com/bc348/assemblies/main.html

Anyway,  these are the values from the leakage tests I performed:

100V:   8 uA
200   36 uA
300    70 uA
400  125 uA

125 uA at rated voltage tells me to replace it, but  there's only supposed
to be 100V on it, so I suppose I might consider letting it go.   On the
other hand,  If I had a 100V rated cap that shows 8 uA of leakage I'd
replace it.

Just trying to muddy the waters a bit.....

73 Mark K3MSB






On Mon, Dec 30, 2019 at 5:38 PM Doran Platt <jeepp at comcast.net> wrote:

> As a matter of fact, I use two of them currently. Both have been
> re-capped, to include the 4 modules and the BFO and Xtal filter.  To obtain
> a better bandwidth, I simply use either of the LF ARC-5 or 274-N receivers
> tuned to 1/2 the BC-358 IF, minus 50khz.  It does wonders on 80 and 40
> meters.  Coupling is done via a small loop at the base ofthe last IF in the
> '348.  No need for any mods of any kind.  I do the same for my ARR-15
> receivers, but tuned to the IF freq. directly (500 khz).  Makes these
> receivers totally usable on the current bands.
> Jeep K3HVG
>
> On December 30, 2019 at 5:21 PM Jim Haynes < jhhaynes at earthlink.net>
> wrote:
>
>
> On Mon, 30 Dec 2019, Whitebear1122 wrote:
> >
>
> Boy those 348’s are gorgeous. Does anyone here actually use theirs on
> the ham bands?
>
> Well I did circa 1958. Those were the favorite receivers of the late
> Bob Weitbrecht, W6NRM/W9TCJ, one of the RTTY pioneers. He developed
> a mod where he used the IF transformers from the LF/MF Command Set
> receivers to get a narrow passband. He converted the 915 KHz IF down
> to 85 KHz, put it through the transformers, and then converted it
> back to 915 KHz and back into the original IF chain. A neat feature
> of this is that you get passband tuning by varying the frequency of
> the conversion oscillator.
>
> Mine was eventually extensively modified. I adopted Bob's narrow band
> IF scheme, but instead of the IF transformers I used a bandpass filter
> found at a surplus store in Chicago. Then I made a new rack-mount front
> panel, and added a chassis on the back to hold the AC power supply and
> the IF filtering and also a product detector. This was used for a few
> years until Bob discovered the Drake 2-B receiver and persuaded me to get
> one too. But I missed the general coverage that the BC-348 offered -
> back then there was a lot of copyable RTTY outside the ham bands.
>
> Jim W6JVE______________________________________________________________
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