One thing that users of external anode power tubes might consider is
filament voltage. My experience in commercial FM broadcast rigs is that
running a PA tube at it's rated filament voltage from day one is a
guaranteed way to shorten tube life.
After installing a new tube in a transmitter, and operating it for a few
days to a week at full rated filament voltage, I would watch transmitter
output power and reduce filament voltage until output power began to
decrease. At this "knee" I would increase filament voltage a couple of
tenths of a volt and operate the tube at that voltage, which generally was a
half a volt, or so, below the "rated" voltage. I experienced increases in
tube life of at least 50 percent based on comparisons to tube log records
when the tubes were installed and run at full voltage for the life of the
tube.
This procedure worked well with 4CX5,000 and 4CX10,000 tubes in Continental
FM transmitters. Determining whether this procedure is valid with a GS-35B
would be an interesting experiment but I would not be surprised if is
applicable to the Russian tube.
73,
Jack, W6NF
On Fri, Dec 18, 2009 at 7:04 PM, Robert Briggs <vk3zl@bigpond.com> wrote:
> G'day all....I note the comment that 500 hours is probably the useful
> life for the GS-35B....I have two amplifiers which are turned on and run
> daily.I use CW only, 160 meters..My original 35B amplifier was put on
> air in March 2006....That tube still runs perfectly...Say 300 days per
> year 3 hours switched on and running say 1 hour CW output that tube
> hasn't missed a beat....My newest GS-35B amplifier put on air last may
> 2009 is also switched on for at least 3-4 hours a day and once more
> shows no sign of losing emission....I think either amplifier won't need
> a tube change for many years....
>
> I don't run either tube hard, using 3500 volts on the original amplifier
> and running it to 1100 watts output.It is capable of much more but why
> flog a willing horse...The newest amplifier has a deficient voltage
> doubling HT supply (AL-80B Transformer) and I run it to 1kw output
> CW....The GS-35B is a willing worker and with a robust power supply is
> quite capable of the US legal limit..I have found no vices with the
> tube...Best advice I have from my own experience is to make sure the
> tube is tuned and loaded properly both input and output and all is
> sweet....
>
> Bob..VK3ZL..
>
>
>
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