I came across the 20EZ7 when they were about a buck each. No more.
An externally hosted image should be here but it was not working when we last tested it.
You could use a bunch of other tubes -- the temptation would be to put a resistor in the filament supply but the current at turn-on is pretty huge. In the case of a 12AX7 the cold resistance is about 13R.
If you put a DN2540 in the filament line, however, you can limit the turn on current and set a value which is appropriate:
If you put a DN2540 in the filament line, however, you can limit the turn on current and set a value which is appropriate:
An externally hosted image should be here but it was not working when we last tested it.
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