the BC250L's grid/driver plate
coil is NOT on a bakelite form. It is a ceramic one, 2 1/2 inches in
diameter.
I still get the exact same grid drive on 160 meters as I did on the
broadcast
band. My problem still remains efficiency, and maybe I'll just have to
settle
with 61% and be happy.
Do you know when the 250L was made?
In their older transmitters they used REAL EF Johnson 833A sockets and
ceramic coil forms. To cut costs, in the later transmitters such as BC1T
they switched to on-site constructed 833A sockets made by turning aluminium
and fitting the receptacles onto a bakelite strip, and the coil form is a
large piece of bakelite. The earlier transmitters used heavy duty
transformers; the later ones use much lighter Electro-engineering
transformers and chokes. They went from a larger driver tube (813) to a
pair of sweep tubes and eventually to 807's, with a about 20% modulation of
the driver rf to maintain sufficient grid drive at 100% modulation.
But the BC1T sounds good and they would run 24/7 with no problem at a BC
station, but the 2-watt carbon resistors need periodic replacement.
Don k4kyv
