Roger K8RI says:
" With external anode tubes and particularly the larger tubes we know that
they continue to get hotter when the fan and power are killed at the
same time."
I'm very surprised to hear this. Here's a counterargument: since the
internal filament, cathode, and grid structures of an external anode tube
dissipate very little heat, compared to the anode itself, I'd think that
once the power is turned off, the anode would immediately begin to cool.
Obviously it will cool more slowly if the blower turns off with the power,
but I don't see why the anode temperature would ever increase after turnoff.
Further, since the anode is made of copper, there is a negligible
temperature gradient between the inner and outer walls of the anode. While
one can argue that it's nice to flush the heat out of the RF compartment
after turnoff, that strikes me as a very modest benefit that doesn't warrant
the complexity of a post-powerdown time delay circuit on the blower.
The situation with glass tubes is different, since the internal anodes
typically show color and run at a temperature much higher than the glass
envelope. Thus, the heat will continue to radiate through the glass envelope
for awhile after turnoff, and an airflow will keep the glass and seals cool
during this time.
73,
Jim W8ZR
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|