[Amps] GS35B Idle current increasing

[Paul Baldock]

Normal power output, but as you would expect I need a little more 
drive as the bias voltage is increased.
Drive power is 10-12W of carrier with around 120% upward modulation, 
so that's about 50W PEP drive, and 1300W PEP output.

I will check the filament voltage, but I think I will find it in spec.

- Paul


At 09:25 AM 3/10/2018, you wrote:
>Paul, sounds to me like your filament voltage may be too low, or else
>you are cooking the grid by driving the tube too hard (grids are
>usually plated with gold or other metal that will evaporate if the
>grid is overheated). Either will greatly shorten the life of tubes
>with indirectly heated cathodes. Are you getting normal power output?
>
>Sent from my iPhone
>
> > On Mar 8, 2018, at 10:09 AM, Paul Baldock <paul at paulbaldock.com> wrote:
> >
> > I built a GS35B amp a few years back to be used with my home brew 
> AM rigs. Initially I set the idle current at around 110mA/4KV 
> requiring about -35V bias. Over a few years of very little use the 
> idle current drifted up so I increased the bias voltage to get it 
> back down. Eventually I was up to -55V with the idle current at 
> around 180mA, and so I installed another tube (purchased at the 
> same time as the first). Same deal as before, started at -35V, now at -55V.
> >
> > Is this 2 bad tubes, or could I be doing something wrong? I'm 
> getting ready to install a third tube purchased from a different source.
> >
> > - Paul KW7Y
> >
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