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In the Forum: Melquiades Amplifier
In the Thread: The one-stage Melquiades.
Post Subject: pulse tubePosted by hagtech on: 4/29/2007
With this tube I would think cathode emission limits lifetime.  Stepping back a moment, I'm guessing this tube is designed for radar operation.  Maybe in an aircraft.  The spec sheet definately talks only about pulse mode of operation.  Maybe it was a driver for a pulse radar transmitter?  What this means to me is that there are some sacrifices made in the tube.  It has a very limited maximum average power dissipation.  This had to be done in order to keep the structure small enough that it would operate at the desired RF frequencies.  It has very high pulse current capability, so the cathode must have extremely high emission, or plate gets starved and curves fall over.

So I have an idea.  For class A operation, the cathode emission is way too high.  We cannot run at the high peak currents because the plate will melt.  Or at least overheat and cause secondary emission problems, glow, etc.  Therefore, I suggest starving the filament.  Let's think about running this tube with 5V heater.  I'll run some sweeps to see what happens to the curves.  I think adapting the tube from pulse operation to continuous mode is no problem.  The lower emission is still enough for our needs, and it has the side benefit of greatly increasing lifetime.

Most importantly, I think we have to keep the plate dissipation way down, like 6W or so.  Cannot let the G2 get too hot. 

I like the direction you are headed.  This tube will sound better and more natural than the 6C33.  But might lack "authority".

jh

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