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Re: Max anode voltage?

Original poster: FutureT@xxxxxxx In a message dated 5/17/06 6:25:11 PM Eastern Daylight Time, tesla@xxxxxxxxxx writes:

Hi Bert,

I tried the debarnacling an 833A tube.  It turns out the manufacturer
put a spark gap in the tube, and it kept sparking at that area.  I got
nowhere with the process.  I didn't persue it or try other types of tubes.


Hi Bob,

If you're really going to push these tubes, you can significantly
increase their operating voltage beforehand by conditioning them
before use. Conditioning (or "spot knocking") removes high points,
whiskers, etc. that can become initiating points for arcing through
field emission. The technique is sometimes referred to as "debarnacling"... :^)

Debarnacling is done with no filament power applied. HV AC (or
sometimes DC) is applied through a 100k - 400k power resistor between
pairs of elements. Sometimes a small (1000 pF - 3000 pF) capacitor is
placed across the elements being conditioned in order to provide a
controlled amount of "blasting energy" without damaging the tube. The
HV supply current is carefully monitored during the process, and the
high voltage supply voltage is slowly increased until sparking first
occurs. The applied voltage is then slowly increased to allow
sparking to condition the tube until the desired voltage is reached.
Although debarnacling is most often used for 10 kV+ power tubes, it
also works for smaller ones as well.

You can get all of the gory details (and lots of other great tube
information) from Eimac's site:

The specifics of debarnacling are covered in Eimac Applications Bulletin #21:

Good luck,