[ARC5] BC453 on 24V - screen voltage

[Kenneth G. Gordon]

On 10 Dec 2019 at 15:44, J Mcvey wrote:

> 
> Apples and oranges, folks!  I'm doing this testing with 25 and 50 volt B+
> which DOES impact performance. This radio did perform as Gordon 
> demonstrated running at normal B+ with the dynamotor supply.
> 
> Lifting the ground lug on the bottom screen voltage divider resistor helped quite a 
> bit at 25V , but still not back to "normal".

In my experiments, I came to the conclusion that the overall best lower voltage for our 
receivers was around 170 VDC, with the screen voltage at the same point.

Reviewing the specs for the 6/12SK7s, we find that the max, and "design center" values for 
plate and screen voltage is 300 VDC, and for a plate voltage of 250 or lower, the screen 
voltage should be around 100 V. From the specs, it appears that allowing the screen 
voltage to equal the plate voltage is just fine. The lower plate voltage keeps dissipation 
lower. The tubes are rated for 4 watts plate dissipationm which IMHO is high for a receiving 
tube..

I also prefer to connect the screen voltage feed to the hot end of the divider resistors, since 
it seems to me that allowing it to "float" is not a good idea. I like voltages to be as steady as 
possible.

Ken W7EKB