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-   -   Doubts on cathode stripping in tubes (https://www.diyaudio.com/forums/tubes-valves/79405-doubts-cathode-stripping-tubes.html)

wrenchone 19th January 2016 03:43 AM

Indirectly, this the rationale for using hydrogen/deuterium as fill gas in HV, high power thyratrons. The lower mass/charge ion has less of a tendency to blow hell out of the large area, high emissivity cathode surfaces needed for a good high power thyratron. Xenon, neon, and mercury fills are used for lower operating voltages.

cerrem 19th January 2016 05:31 AM

There are cases of cathode stripping during start-up of receiving tubes where the Heaters are "floating" on a DC voltage derived from the B+...
The damage occurs due to the Heater to Cathode voltage is greatly exceed for a short time before the B+ pulls down to it's loaded state.... Very repeatable....you can hear the clicking sound of the arc..
Simple fix is to put a protection zener on the voltage divider ...this way the zener clamps only during start-up, preventing an over-voltage on the Heater...
Problem 100% solved ...

Guido Tent 19th January 2016 07:47 AM

Quote:

Originally Posted by Bandersnatch (https://www.diyaudio.com/forums/tubes-valves/79405-doubts-cathode-stripping-tubes-post4587040.html#post4587040)
If that were the case, no IDH rectifier would survive turn-on.
cheers,
Douglas

of course I am talking long term use, incidental cases do not harm

Uunderhill 8th April 2016 07:02 PM

To point out, here is an article called Kindness to Filaments by John Harper.
http://www.john-a-harper.com/FilamentHeating/index.html
To be kind to the heaters, he suggests doubling the heater supply voltage,
but a resistor is connected in series with the heaters.
The value of the series resistor is the same as a warmer up heater.
.

DF96 9th April 2016 09:24 AM

Normal AC heater supply is sufficiently kind for most purposes, as the transformer resistance limits surge current.


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