Hi Tom,
this tube used to be the most popular for "big contest" amps in pre-GU78/84
era in Ukraine, but with the current prices and availability of modern tubes
it has a good chance to come back :) - GU5b's are still relatively cheap and
easy to find.
Played with them some 10 yrs ago, as much as I remember at 6 kV gain was
still below 10 db, but never
tried to optimize the circuit - it was more than enough.
She is a nice DX-spot killer because it's instant-on and powerfull, with say
GU-81 in driver (another popular cheap instant-on tube). If preconditioned
well, works stabily on all bands.
Most builders here used its original grid ring with 8 K15-U 470 pF 2 kV
caps, I see these rings offered on Ebay sometimes.
Anyway majority of amps on GU-5b used by those few "crazy" hams are retired
modified commercial transmitters R-110 called "Viaz", with 2 of them in
push-pull, driven by 2 GU-81 in PP too, feed by 14,5 kW 3 phase plate
transformer :).
73, Roman US5WDX
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