wrote:

"** The load impedance is doubled, since the max tube current cannot increase.

Double voltage into double load = double the power.

I think you got this ****ed up somehow.


** Like hell I did.

Try reading it AGAIN !!!

IF you double the voltage into double the load, the CURRENT stays the same.

But double the voltage at the same current is TWICE the power.

Power = V x I



"Having the screens glowing bright is the biggest killer of power tubes."


Perhaps you are older and thus have more knowledge then I on some of
this. From what I understood from the old days, tubes (valves)
generally break down due to the cathode nit being able to put out
current, and that is where all the current comes from.

However of course there can be other failure modes. Are you saying
that some sort of arc or leakage is damaging the valve ?


** Any data sheet will quote max screen dissipation - usually only a few watts.

The fine steel wire will glow red or even white if the rating is exceeded.

Then guess what happens ??

If the screen supply voltage is too high, it take excessive current whenever the plate voltage swings low under load.

Data sheets reveal this as an increase in AVERAGE screen current at max signal.

Screen dissipation = V x I average.



..... Phil