[ARC5] BC-453 drift test

[Bob kb8tq]

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 ….

Bob

> On Jan 11, 2018, at 12:42 PM, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:
> 
> On 11 Jan 2018 at 9:38, DSP3 wrote:
> 
>> I certainly concur.  I run 4 receivers and use a nominal B+ of about 
>> 160v.  Current measures about 40ma, max.  There is no measurable 
>> drop in anything except perhaps total audio output power, certainly 
>> not sensitivity or BFO operation.  The R-25A is used as a tunable IF 
>> for the ARC-2 and, as performed by others, find drift after a nominal 
>> worm-up time to be very, very low.  Granted, digital usage is not a 
>> consideration at this QTH.  That said, I also run B+ on BC-348 
>> receivers, et al, at about 180v with, again, no degradation. 
>> Jeep - K3HVG
> 
> As I have mentioned more than once here, I have found, after much experimentation, that 
> our receivers seem to work best at a voltage of about 180 VDC.
> 
> However, I also found that moving the screen voltage lead from the junction of the two big 
> black resistors in the rear to the "hot" end made a significant improvement in sensistivity 
> without degrading drift.
> 
> Looking at the specs for the 6/12SK7 tubes, we find that 180 V is "about right" for those 
> tubes' screen voltage. Typical specs are 100 V, but that would require changing resistor 
> values, and I believe in the KISS principle.
> 
> Ken W7EKB
> 
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