Well, I have finally completed this project...All electronic circuits
perform faultlessly...I am using a russian GS-31B in this project...I
will later replace it with a GS-35B....Running conditions as
follows...2800vdc under load @ 900ma with 60 watts of drive produces a
tad over 1300 watts carrier output....This is close to 55% efficiency,
about what we can expect from these tubes...Grid current loads to around
280ma...I have not increased drive past 60 watts at this stage..
In regard to water cooling....I built a small water manifold which
screws on to the tube in place of the very inefficient air cooler...My
home brew cooler has a solid copper center for good heat sinking....I
had good advice from Roger K8RI and Tom DJ5RE regarding hose length from
the amplifier to the water reservoir and water cooling in
general....Rule of thumb 1 meter per 1000 volts...I am using two 3 meter
clear vinyl water hoses...The hoses have two copper joiners at the
reservoir bonded together and earthed through a 1ma meter to measure
leakage current through the water lines...Initially leakage is 320ua
cold and 500ua at 40C...I have been doing all my testing with 10 liters
of pure water at this stage..
Running 1000 watts of carrier, fast CW dots at 60wpm rate and also some
SSB for 1 hour continuous warms the water to just 40C from cold.....I am
not using a heat exchanger at this stage...I am using a 1000 liter per
hour pond pump to move the water...At a 3 foot head I am getting 4.5
liters per minute through the tube manifold...
I still have the amplifier under test in my workshop for now as I may
make a few adjustments to the Pi output network as I want to increase
the Q slightly....Loading is sluggish....
The bottom line is that the amplifier runs almost completely
silent....Eliminating any blower noise which was my goal....I am very
pleased with the outcome and it has been worthwhile project....
Bob..VK3ZL..
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