>
>I'll ask again:
>
>What is the standard TL922 parasitic suppressor?
>
>If it's the usual carbon resistor/shunt inductor, I could well imagine
>parasitics starting after a period, as the resistor has probably got cooked.
>Especially when we take into account Tom's comments on seal temperatures - I
>presume he has evidence for that, or he wouldn't have said it.
>
I doubt that Tom has any such evidence. I tested the 922 cooling system
and found it to be surprizingly efficient. Anyone who looks over the
tubes in a TL-922 knows that the Eimac ink is red.
>Under those circumstances, a nichrome resistor may well perform better, in
>that it doesn't cook and go high/open so easily.
>
>As to the 'bangs' appearing because of parasitics, I am highly dubious. I
>could see a parasitic causing enough heat in part of the tube structure to
>release gas
>in a burst, causing an arc which cleans up during the following cooling
>period.
Arcs displace metal. They do not clean up. It is my opinion that there
is quite probably no such thing as disappearing gas that vanishes as the
shorted tube is being high-potted.
>I can see a VHF parasitic causing enough grid dissipation to boil the gold
>off a grid.
As I understand it, gold-sputtering involves heating only the surface
atoms of the gold plating on the grid. In all of the examples I have
seen, less gold evaporates from the ungrounded end of the grid more than
from the grounded end -- not unlike current distribution in a vertical
antenna.
>And I have problems seeing the VHF parasitic circuit having
>sufficient Q to get the step up to burn bandswitches.
>
... not a good description of what happens. The mechanism that
transforms Z and burns the bandswitch is entirely within the Tune-C. .
Have you seen the QST photo of the burned 922 bandswitch? (p.33, Oct,
1990)
>
>
cheers, Peter
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|