Yes - I decided against the programmable constant cathode bias because, even though the dissipation requirements were modest, it was going to be inside the chassis, with no fan planned, directly underneath the EL34's - and I wasn't sure if the box would fill up with heat or not. I was considering posting the other board for comment, but this was a thread about schematic drawing software. But it uses a similar design to what I'd posted before but driving a negative grid bias voltage instead of sinking the cathode current and holding it constant voltage. I was kinda bummed, because I was really curious to try it, but I was up against 1) getting rid of a handful of watts of heat in an unvented chassis, and 2) when I started considering source followers on the grids, the additional aggrevation plus the heat concern made me decide to ditch it. Some day I'd like to try it though.
It basically takes that 0-5v programming voltage and turns it into 0 to -80v, but that fault line goes high whenever either bias voltage is more positive than 20v or so and shuts it down if the bias circuit isn't ready/working/blew fuse. The gate drive and bias control is basically the circuit gingertube posted in the AB2 grid stopper thread, with a PVI in the error circuit / gate drive for bias control.
It basically takes that 0-5v programming voltage and turns it into 0 to -80v, but that fault line goes high whenever either bias voltage is more positive than 20v or so and shuts it down if the bias circuit isn't ready/working/blew fuse. The gate drive and bias control is basically the circuit gingertube posted in the AB2 grid stopper thread, with a PVI in the error circuit / gate drive for bias control.
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