In fact you could bias the grids for AB1 and cathode feed (4) 4x150A or
4cx250b and get extremely low distortion due to the very low grid current
drawn. But you will need bias supplies. And reduce filament voltage from
6.3 to 6.0 volts. 4CX150A and 4CX250B have the same electrical
characteristics but the 150s are much cheaper. Keeping the plate supply
voltage the same prevents having to go to greater spacing it plate tuning
capacitor, changing out parts such as bypass capacitors and plate coupling
capacitor and modifying power supply to doubler and adding more
electrolytic capacitors.
Grid driven would allow you to use QRP rig as exciter.
73
Bill wa4lav
At 09:16 AM 6/28/2004 -0400, Val" , <Amps@contesting.com> wrote:
Maybe go to (4) 837's or modified 1625's. Not as much power ( they were
really pushing the sweep tubes anyway).
Look at the LA-400 amplifier made by P&H on bama.sbc.edu. ( no www). 1200
volts is just about right. Or you could run
tetrodes (4) 4x150A and get more power (AB1=620w, AB2=850w) than a pair
of G17B's and the 4x150A tubes can be gotten cheap. The sockets with out
built-in by-pass capacitors are fairly cheap ( buy surplus T-195 modulator
tube assemblies possibly from Fair Radio).
73
Bill wa4lav
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