AFAIK a tetrode in grounded grid doesn't give you much more (if any)
gain than a triode in grounded grid, but you still need all the special
care and feeding of the screen.

I agree with you opinion.

So why not just use triodes?

My experiences are only in triode PA and I have a lot of tetrodes and
pentodes "unemployed" :-)))

Better yet, why not use the tetrodes in common-cathode service, and get
1000 watts out for 1-10 watts in?

Sure, but I don't have experience in tetrode or pentode PA and the screen
grid managenement, isn't a walking...
In all know books and websites I don't find a valid explaination of this
matter....

Thanks!!
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73's de IZ5FCY Roberto