[Amps] 4CX250 bases

[Steve Thompson]

David Lisney wrote:
> Hi, my own little tetrode amplifier uses a conduction cooled version of the 
> 4CX250, the CCS1, my screen supply is merely a pair of BU208 television 
> transistors, one configured as a constant current source, the other as a 
> shunt regulator. If the screen of the valve "tries to hard" to climb towards 
> the anode voltage a thyristor clamps it down to chassis/cathode potential.
snip
> Possibly a further consideration with these valves is to protect the bases, 
> I don't know just how much they can stand voltage wise on the screen bypass 
> capacitors... maybe someone else can comment?
I've just put a couple of bases on hipot. One is a Johnson 
124-110, the other is by AEI (quite common at UK rallies). 
Both look very similar to the SK600 family.

On both, discernable current (<1uA) starts to flow at a bit 
over 2kV.

Steve