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.
During my initial phase of cutting a number of striplines and altering the
coupling trying to get reasonable power out of the amplifier (2m) I used a
very sick CCS1, the screen clamping circuit worked smoothly and I had no
fireworks or destroyed components, not even a blown fuse. Just a case of
switching off, waiting a few seconds then back on again....
The valve I was using at this stage had suffered all sorts of major abuse in
a 4m PA but I did not notice any further harm coming to it performance wise
despite these calamities, ( I swapped it for a new one once the amplifier
was completed) the new one has never tripped anything....
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?
Current project is a pair of GS-35b in an HF PA, power output will be
crippled by power supply limitations..wow these valves are heavy!
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|