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'load lines for dissimilar output tubes?'
Author:Malcolm Irving (registered user: 29 posts )
Date: Fri, Mar 17th, 2017 @ 09:23 ( . )

Yes. The total plate current of the two dissimilar tubes would correspond to a load of 8k. But I expect the 6L6 will take more of that current than the 6V6.
I think you could decide on the B+ and the screen voltage you are going to set for both tubes and then look at the plate characteristics. The two load lines both start at the B+ value on the horizontal axis. You then need to juggle around with the slopes of the two load lines, so that total plate current stays the same (as for two 4k loads). If you move one line up by 5mA on the vertical axis the other line has to come down by 5mA. Keep juggling until you find a pair of load lines so that at a given grid voltage on the load lines (say -10V) the corresponding plate voltages agree.
Assuming the 6V6 takes less current, its load line could go ‘below the knee’ – so watch out for screen current on that one – a good size screen stopper may be needed.
Would you set the same bias voltage for both tubes, or with some added complication you could have different biases?
The output transformer would just see the sum of the two currents – so no problem there, that I can see.
My own gut feeling is that there won’t be any more stability problem than usual.


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Replies:
--* load lines for dissimilar output tubes?
3/17/2017 @ 14:17--CChurchill
3/17/2017 @ 14:20----CChurchill
3/17/2017 @ 14:54----Malcolm Irving
3/17/2017 @ 19:51------CChurchill
3/18/2017 @ 13:49--tapehead ted
3/18/2017 @ 15:21----Malcolm Irving
3/18/2017 @ 15:35------tapehead ted

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