[Amps] What Is TheOptimum Bias For GS-35b Tubes?

[John Lemay]

That sounds like a lot of bias current. I have two commercial amps each with
a single tube. They recommend bias at around 100mA and the plate voltage is
around 3600.

Regards

John G4ZTR

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Mel
Sent: 24 June 2010 18:36
To: Amps at contesting.com
Subject: [Amps] What Is TheOptimum Bias For GS-35b Tubes?

I have a GS-35B Bias question.
I constructed a 2 tube GS-35B amplifier; it has separate filament
transformers and bias systems for each tube.  My transformer runs 4200 VDC
unloaded; I set the Zsac for each tube separately, I have each tube running
at exactly 425 mills at idle.  At 425 milliamps, the X-former drops to 3900
VDC (with one tube disabled by removing cathode fuse).   Both tubes are set
to draw the same amount of current.
 
When I put both tubes in service, instead of getting 850 mills of Zsac, my
idle current is 740 milliamps and my B+ is at 3750 VDC.
 
With RF drive the B+ dropped to 3375 VDC @ 2.0 amps and delivered around
4000 watts output; at increased drive levels, the B+ did not drop any lower
than 3375, it  (the X-Former just drew more current from the mains; I took
plate current up to 3.5 amps and B+ held solid).
 
What’s the optimum level of bias to run on a GS-35B and, based on my
observations, should I crank my bias up a little higher in setup knowing
that when the 2 tubes are run together they drag the B+ down which changes
the affect of the bias setting?
 
There is a lot of information at GS-35B DOT com but, I would really like to
hear from someone with recent experience on their construction / conversion
using the GS-35B tube.
 
koØm
 
http://www.network54.com/Forum/142608/
 
.
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