Re: 4-125A, vacuum tube do's and donts

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Fucian-at-aol-dot-com>
> 
> In a message dated 4/8/02 1:49:53 PM Eastern Daylight Time, tesla-at-pupman-dot-com
> writes:
> 
> << Matt,
> 
>  You are wise to ask this question, since tubes are susceptible to
>  destruction in various ways.  First of all, never let the filament
>  voltage go more than 5% over the rated voltage.  Never let the
>  plate get too orange-red.  An orange red color is normal, but
>  you don't want it to get orange or yellow.  A good way to run
>  the 4-125A's is to tie the both grids together and run them as
>  a triode.  Circuit values have to be correct for that.  Use a
>  plate lead choke/resistor to prevent tube damage in the event
>  of an internal arc-over.  This tube can acually withstand a higher
>  plate voltage of 4kVAC or so.  All the adjustments are critical
>  for best results in a VTTC.  This tube can give a 12" spark or so.
>  Run the tube only in an upright position.  If the tube gets very
>  orange, but the spark output is weak, then things are not adjusted
>  correctly.
> 
>  cheer,ss
>  John

	I'm worried about the recommendation to tie the grids together and run
the tube as a triode.  Has anybody checked with Eimac to see if this
mode of operation is OK?  With some tubes it is, but with others may
result in damage to the screen.  I can't find my Eimac book "The Care
and Feeding of Power Tetrodes", which has information on the subject. 
Maybe someone else has one.

Ed