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First Bench Test

I've come up with a list of tubes that will probably work in this application without a negative bias supply under the chokes. I won't bore the group with all of that, but I did try the first tube tonight, a 6K6GT in triode mode. Here are the preliminary results:

With exactly +300 applied between the anode and ground, the choke drops 30.1V. It's actual resistance is close to 2.3K, so that equates to 13mA through the choke and tube. At this current, the 6K6 is dissipating 3.5W. This is somewhat less than half the tube's maximum rated dissipation.

With 20V pk-pk applied to the grid (the maximum output of my function generator), the cathode produces 17V pk-pk into a 12K load. That's a modest 1.4dB loss. Frequency response is very good. 10Hz is down just a little (sorry, just viewing the scope for now, no numbers yet). On the high end, it's flat to 500kHz, then there's a gradual roll off that appears to be roughly 3dB at 1MHz. This is confirmed by the virtually perfect response to a 100kHz square wave. I have roughly a dozen more tube types to try - 6L6, 12B4, 6AS7, 6V6, etc. I think this particular combination will be hard to beat though.

The schematic of the test circuit is below:






Edits: 05/19/17
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