I think those tubes were strictly made for military use and that those
ratings are for inside a tank or war plane. They probably pulled the
tubes after that many hours.
73, Alek.
VK6APK
On 4/05/2017 8:20 PM, JEREMY ENGBROCK via Amps wrote:
I have recently purchased a set of GS1B tubes that were listed as GS31B tubes. The main difference as far as I can tell is the GS1B spec sheet says the rated life is over 250 hours and the GS31B life is rated at over 1000 hours? What is the limiting factor in the life of these tubes? can I really expect the heater to burn out or the emission to fall off that fast? I know that these are Mill spec ratings for use at 30 cm wavelengths so my mileage in an HF amp will vary, but 250 hours kind of makes it seem worthless to even attempt to build an amp around it. These have a 1975 date code and I have already burned in the heaters for a little over 2 days, so yes they are about 42 years old.
The next question is about using DC for the filaments on an indirectly heated cathode tube like that. I have a nice switched DC supply gathering dust that I have been thinking about using as a filament supply. This will let me have tighter control over the heater voltage as the incoming line sags and surges. Is there any specific reason that I wouldn't want to use a DC supply on the filament vs a a small transformer. I have heard tales about using dc shortening the heater life due to a whole bunch of different reasons, but I don't have any fact or experience to draw on? Other than economics what difference does it make what type of current is used to power the filament? Will I burn up the supply? I am not sure if the negative terminal is connected to earth or not?
What are your thoughts?
73, Thank You, Jeremy Engbrock N0NZG
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