>Many thanks to those who replied to my request for 4CX1000A advice. I now
>have the info I needed in regard to the question about filament/heater
>chokes. However, the other question I asked remains pretty much unanswered.
>The question was:
> Many references have been made to grid damage
> in the 4CX1000A and similar tubes; what are
> the detailed symptoms of said damage? (Assuming
> the tube still sorta operates)
>The only answer I received (from Rich Measures) was:
>>The grid in the 8168/4cx1000A is barely visible to the naked eye.
>>Presumably, when the 0w [sic] grid dissipation rating is grossly
>>exceeded, the tiny grid wires melt.
>Forgive me Rich, but I don't think that answer directly addresses the
>question. Perhaps you are just being sarcastic by saying if you get any
>grid current the tube is destroyed.
No. Any current is obviously not capable of melting the grid wires. My
guess is that a few tens of mA for a few seconds would not hurt, despite
Eimac's 0w rating. My guesses on the symptoms of grid damage would be a
grid to screen short, a grid to cathode short, or, if all of the melt
debris falls straight down, high, uncontrollable zero signal anode
- I have heard of only one case where a kaput 8168 was autopsied. The
owner did not say why the tube failed. He commented only that the grid
wires are difficult to see because they are so tiny, and each grid wire
being placed directly behind each screen wire
>Now, I believe the lack of response may be attributed to one or more of the
>1) No one really knows squat about a 4CX1000A.
>2) Somebody knows, but he ain't talking.
My vote is for lack of info. . Very few people are into autopsing. I
do tubes. My cousin Virginia does humans. Maybe it runs in the family
>3) The whole idea of 0 watt grids is B.S. and you can run moderate grid
>current forever as in the 4CX1500. (Or at least until the neighboring hams
Agreed. In grid-driven amplifiers, grid current makes SSB doo doo. It
is my opinion that SSB doo doo stinks.
R. L. Measures, 805-386-3734, AG6K
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