Larry and all, Eimac typically says 150% of normal current, I believe, for TT filaments. Most big toobes use either a ramped up variac or power supply, or a current limited transformer that has a gap
They say twice for most tubes we deal with. The exact text says limiting current to two times the operating value helps reduce damage (movement) from repeated filament thermal cycles. I've never see
The way Henry deals with #2 above is inserting a 10 ohm 50 watt power resistor in series with one side of the 240 volt primary of the filament transformer. This is on their 3X3 amps. There are 6 tap
There may be some truth to this because the filament emission loss is related to the filament temperature and the amount of time that it is hot, with or with out anode voltage. Running the filament c
I would love to hear the theory behind that and John and all, I wish I could provide more background. It's been a lot of years and at the time I was still in my "cowboy" era where I only cared about
Interesting, because when we would get a low emission batch of 3CX1200's they would have us run the tubes for days without any anode voltage or current at extra filament voltage. It would always bri
Tom, You are correct, for Eimac its normally stated as limit the current to 2 x the operating current on turnon. I was guessing conservatively. I checked and the same thing applies with the larger tu
I suppose the knowledge of filaments has advanced since 1942, but there was a special reason to "make do" when the Radio Handbook was published. There is an ad in the back for RCA Transmitting Tubes.
Author: Peter Chadwick <g3rzp@g3rzp.wanadoo.co.uk>
Date: Sun, 11 Feb 2007 13:26:41 +0100 (CET)
says limiting current to two times the operating value helps reduce damage (movement) from repeated filament thermal cycles.< But we all know that filament movement is caused by VHF parasitics, don't
Author: Peter Chadwick <g3rzp@g3rzp.wanadoo.co.uk>
Date: Sun, 11 Feb 2007 13:34:14 +0100 (CET)
There can definitely be a problem running oxide coated cathodes for a long time without drawing current: it leads to a build up of cathode interface resistance, and according to one of my textbooks (
"There can definitely be a problem running oxide coated cathodes for a long time without drawing current: it leads to a build up of cathode interface resistance, and according to one of my textbooks