I have problems debugging a FL2100B after I installed a pair of Svetlana
572B.
It has blown several 33 ohm grid resistors with a big bang. The grid is not
directly grounded but decoupled with 200pF. Bias is supplied via the 33
ohm.
Bias supply has been modified to a voltage doubler a la Svetlanas
suggestions and the tubes are cut-off in stand by. No-signal current is
adjusted to 30 mA.
I have had this problem occasionally with the original Cetron USA tubes,
but after I changed the grid resistor to 47 ohm, 2w, I have not seen this
problem. However with Svetlana tubes the big bang occurs nearly
immediately. Luckily the tubes have survived so far.
Any suggestions?
73,
Hans, OZ5DX
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