On Sat, 2009-01-17 at 18:27 -0700, jack wrote:
> bringing the tube up to voltage slowly also extends the life. Eimac (years
> ago) suggested the best application would be to put a variac in the high
> voltage power supply primary and run the voltage up manually. however Vern
> Campbell now a silent key, drove a 3-500Z with another 3-500Z until it gave
> up the ghost to see how long it would run. he said it lasted a week running
> as hot as he could manage. at times Eimac would receive a tube back from the
> user that had become gassy. they would run that tube hot for a day and then
> send it back to the consumer. i have no idea how the present tubes are
> manufactured however so cannot vouch for the new issue tubes.
> jack ak7o
>
The filament thrives more than the plate when brought up slowly. Most
tubes larger than these 500 watt plate dissipation rating tubes have a
peak filament or heater current rating on the data sheet. So its
necessary to insert impedance or use some sort of a slow start. The
tungsten filaments run hot enough their cold resistance is 15 or 16
times lower than hot, so they will try to draw a big turn on surge.
Running a tube hot activates the getter deposit on the glass and cooks
adsorbed gas from the rest of the metal and so gets that gas caught on
the getter deposit. They used to do that with ceramic tubes like 4CX250B
too.
73, Jerry, K0CQ
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|