It sounds like they were connecting the 813s as zero-bias triodes, more
often done in modulator service. Don't know why they'd do this instead of
run them GG in this application, though, unless there was an appreciable
difference in gain. Maybe the guy just wanted to experiment with something
"different."
I don't see how the grid current meter connected as you described would
register any grid current at all, 'cuz I can't see that the control grid
would go positive wrt the cathode in that configuration. Does it move off
the peg at all??
73,
-Larry/NE1S
Bill Fondren writes:
I recently traded for a linear that has a strange input circuit, at least to me.
The amp is built in a 18 " Bud rack mount cabinet weighting about 150 lbs. To
heavy for 1 person to handle so I deceided to split the RF deck from the power
supply and put it in a taller cabinet along with the exciter. No info was with the
unit. I have used it a couple of times and it works fine . It uses a pair of 813's
in parallel. I started to draw out the circuit finding that the drive goes to a
tuned circuit and then to the sceen grids of the 813's. The control grids are
connected together and go to a 10K resistor, the grid current meter and then to grd.
No connection to the drive circuit at all other than the interelectrode cap. I
guess. The plate circuit seems to be normal. Just wondering if any one has seen
something like this before. Bill K5PML
