While replacing two exhausted 6JE6A tubes in an SSB transmitter with a pair
of identical tubes, I noted that, despite the new tubes are NIB, their
idling currents are significanly different from each other. To be fully sure
that the difference was due to the tubes, I tried to exchange tubes across
sockets. Moreover, during the test, I verified that no RF drive reached the
tube grids and that no self-oscillation was taking place: the difference was
really due to the tubes.

As those tubes are not too common nor very cheap either, I would like to try
a workaround for balancing them.

Looking at the schematic diagram I determined that modifying the circuit for
having two separate grid bias controls, allowing independent bias
adjustment, would be rather complex.

On the contrary giving a small negative voltage to the suppressor grid of
the strongest tube would be very easy.

I am aware that balancing the idling current does not necessarily imply that
tubes remain balanced also when RF drive is applied to their grid and, in
that respect, I wonder whether any one has got experience with balancing
tubes by varying the suppressor grid potential.

Thanks & 73

Tony I0JX
Rome, Italy