[ARC5] BC-375 Re-Tube Project- Scratch Three

[Kenneth G. Gordon]

Dave:

Have you yet tried connecting the screen directly to G1 for the 
oscillator?

Ken


On 18 Nov 2013 at 3:10, David Stinson wrote:

> Three candidate tubes for the  
> "Cheap Tubes for the BC-375" project have disappointed.  
> 1625, 837 and 7984 will not "hold up" in this service.
> Once the screen voltages are dropped to spec,
> the tubes lack the gain to oscillate reliably, even 
> with heavy "gimmick" cap coupling between grid
> and plate in the OSC stage.
> 
> Running the screens above spec will make the tubes 
> "sound" good- for a little while.  
> Then the screens give it up.   The 837 is an exception.
> It's screen is tough and it stood-up well to being 
> directly connected to the plate.  
> But even with heavy feedback, the 837 just won't
> deliver "keyable" oscillation.  Starts too slow and 
> yelps like a houng dog.
> 
> Not giving up.  There is an answer- just got to be persistant.
> In the mean time, lowering the B+ to 500 Volts, adjusting the 
> thermal compensation capacitor, properly adjusting the keying relay
> and using a "clean" 211 in the MO have tamed the 375 on 
> both 40 and 30 meters to at least "Classic Exchange" standards.
> 
> More work to be done.
> 
> 73 DE Dave AB5S
> 
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