[Milsurplus] Need BC-348 Expert!

[mac]

Mike

A 100K resistor placed as you describe would serve to reduce the gain  
of the 2nd RF stage by some amount.  Not included on the R and other  
models
as you report.  I would say leave it out , do the rest of your  
restoration, get the receiver running and then experiment with the  
resistor in and out of the circuit
and see what happens.

Dennis D.  W7QHO
Glendale, CA

************

On Aug 25, 2013, at 8:09 PM, Michael D. Harmon wrote:

> I'm rebuilding a BC-348-P which had been modified (poorly) sometime  
> in the past.   I'm using the TO 08-10-119 manual downloaded from  
> Andy Moorer's BC-348 site.  With a date of 15 DEC 42, it's not the  
> latest BC-348-P manual I have, but it's by far the best print  
> quality.  Both the parts list and the schematic show a 100K, 1/2W  
> resistor (Ref # 48-5) between the screen and cathode lines on the  
> 2nd RF tube (VT-86).  However, this resistor is NOT shown in the  
> wiring diagram - not the main chassis, the terminal strips nor the  
> tube shelf.
>
> At first, I thought the discrepancy was due to an engineering change  
> that either added or deleted this resistor, but every schematic and  
> parts list I have shows this resistor, and none of the wiring  
> diagrams show it.
>
> The parts list describes the resistor's function as 'bias control'.  
> The other BC-348 manuals (B, H, K, L, R, S) don't show this  
> resistor.  In fact, one of the manuals I have shows this resistor X- 
> ed out, as well as the 3.5K 'noise compensator' pot (Ref # 58). I've  
> been somewhat ambivalent about whether to leave the 'noise  
> compensator' pot connected or not.  It was designed to reduce the RF  
> gain as the frequency went up on each band, but I'm pretty dubious  
> about the benefit of this feature when used in ground-station  
> applications.  In fact, I can see that this 'feature' might be at  
> odds with getting the best performance out of this receiver.
>
> What do you experts think?  Should I leave the 'bias control' pot  
> out?  What about the 'noise compensator' pot?   FWIW, I'm not trying  
> to build a museum piece.  I just want a BC-348 that performs well.
>
> Thanks!
> Mike, WB0LDJ
> mharmon at att.net
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