[AMPS] parasitics

[m.j.willis@rl.ac.uk (Mike Willis)]

>Is there a case for adding a shunt suppressor load to cope with when
>there is a high Z anode load at vhf - a state where the voltage gain
>will be highest? Mental arithmetic makes me think it would have to be a
>C/L/C high pass filter so as not to cook things on 10m.
>
>Steve
>
Almost certainly, but it is difficult owing to the EHT. If you design the
PI-L circuit correctly, it will act like a low pass filter so ought to never
be high Z at VHF. This does mean you have to use VHF techniques even though
the amplifier is at HF. Short ground paths, thick conductors and multiple
capacitors (i.e. 1 good low value VHF type in parallel with the HF one) 
for the DC block would be a good idea. It is better to use an HF transistor
that
has a gain drop off than a VHF one in an SSPA, so I would expect the same
to be true of valves. E.g. a 3-500Z amp would be easier to tame than (say)
a 3CX800.


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