[ARC5] BC-453 drift test

[Kenneth G. Gordon]

On 11 Jan 2018 at 13:17, Bob kb8tq wrote:

> Hi
> 
> Well, I can tell you from direct experience back in about 1966 that
> breaking the junction between the two big resistors and dropping the
> screen voltage to zero has a "quieting" effect on a 453 .... 

Ha ha! :-)

I'll bet it would!

Those two resistors at the rear drop the screen voltage to almost exactly 100 VDC, when 
the B+ is 250 VDC. 

If everything is left as is in the receiver, when the B+ is dropped, the screen voltage also 
drops, and according to the specs on the 6/12SK7, "typical" screen voltage is 100 VDC, 
while maximum screen voltage is 300 VDC.

In any tetrode or pentode, screen voltage has far more effect on plate current than almost 
any other parameter.

Those who run their "ARC-5" receivers on voltages lower than the nominial 250 VDC, really 
should "adjust" the screen voltage upwards, especially those who operate their receivers on 
something like 24 VDC.

At that low voltage, increasing the screen voltage to at least 24 VDC will show a significant 
improvement in receiver operation, and all that takes is moving one wire.

Ken W7EKB

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