I built several amplifiers using the Super Cathode Driven circuit a few
years ago using pairs of 4CX250R and 350R tubes.
I tied the grid to the cathode and directly grounded the screen.
I found that the input tuned circuit of all these amplifiers was fairly
critical to get enough drive on to the tubes and used a tunable from the
front panel L network.This gave optimal drive.Grid current was usually
around 2ma fully loaded to give highest power output.I never had the
test equipment to measure IMD.The gain is very low in this confuguration
however and I found that 6 or 7db was all I could coax from the tubes.
I ran the tubes on a fairly stiff 2500 volt Ht supply and never has any
instability problems.Most of these amplifiers are mono or duel band
units 1.8mhz to 14 mhz and are all still in use in VK.
I wouldn't recommend anybody bother spending time building this type of
amplifier from scratch with the availability of GI-7B triodes in
plentiful supply these days but I most certainly enjoyed the experience
of homebrewing these amps and using them.
Greetings from Oz......Bob VK3ZL..
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