Hi Mike et al
Interesting problem - are you measuring the grid bias
and screen volts at the socket pins, or remotely (e.g.
some test point) ?
It could be several things, but I'd put my money on
a grid bias problem - maybe a series resistor increasing
in value and reducing the (-55V approx) fed to the grids.
I don't think it's likely to be a fault with one of the tubes,
but you can't assume anything !
73
Chris GM3WOJ
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