Link
BOM
Runs on +/- 400-450v
all trim pots responsive.
Bias set at 80% .8V across 50R for now
Scope with 100x probe = input at 1x
Mouser slow this week so using MJF15030 (backwards) for the KSC2690A's
Balance adjust to 0V
Offset trim adjusts -132v to -146v so need to track that down... may change when using + / - 400v and 2690A
led's lit, no smoke, stable voltages
If you need to
change the 250R below the offset trim pot for adjustment range
Its about 1.4v per ohm change
less ohms= more negative offset
more ohms = positive voltage change
current thru the tube designed to be 20ma, so a bit more than previous
driver transistor is ksc2690a only, dissipates a little less than 1W, needs very small heatsink
you loose about 45 volts across the tube, so +/-450 is ideal
You can adjust the cascode without hooking up the high voltage power supplies, by using a 15-20 volt supply (2 nine volt batteries in series will do).
Connect the positive terminal of the battery to the positive PS terminal on the board and the negative battery terminal to the end of the 100 ohm resistor connected to the trim pot.
Then put a meter across the sense resistor and adjust the trim pot until you get the right voltage for the current source.
HEAT is 16 watts per channel for the 10m90s plus another 10 watts for each power supply
Update-- Flaming resistors...
when changing transistors I left a metal leg shorting to B-
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