[ARC5] BC-348

Mon Dec 30 21:36:21 EST 2019

 I think "tubular" may have been a reference to the old tubular ceramic caps which looked similar to a small power resistor or like the ancient resistors with the wires wrapped at the ends, but were hollow. I'll look to see if I have one to take a picture and send it to the group.
In my experience, these old ceramics hold up very well. You can leave them there.

    On Monday, December 30, 2019, 7:50:09 PM EST, CARL HUETHER <k1uhy at comcast.net> wrote:  

   Tubular as in round is as far as they got. Other gear including ham might also include "paper"  Actually Im surprised it wasnt a bathtub cap.   

 On December 30, 2019 at 6:21 PM Mark K3MSB <mark.k3msb at gmail.com> wrote: 

   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______________________________________________________________   ARC5 mailing list   Home: http://mailman.qth.net/mailman/listinfo/arc5   Help: http://mailman.qth.net/mmfaq.htm   Post: mailto: ARC5 at mailman.qth.net   
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