On 01/23/2011 08:07 PM, Nordic Breeds WA4VZQ wrote:
"Radio wrote in message
...
I WANTED circuit for 80/40 meters CW transmitter with VFO , 2 or 3
tubes with a final valve 5933wa.
can you help me
TNX Frank


To add to good advice Scott and Kenneth have given, circuits using the
6146 would also be suitable to copy. I would use a VFO operating on 1.75
to 1.8 MHz for stability with the first tube, doubling in the second
tube. On 80-meters the final would operate straight through. while on
40-meters, you would double in the final. Such an arrangement would
generally not require neutralization with the good shielding of the 5933
(a mechanically ruggedized 807).

73, Barry WA4VZQ


The reason that the 6146 tube generally requires neutralization and the
807 does not is because of the higher gain of the 6146. The 6146 will
draw greater plate current at a lower screen voltage (with the same
plate voltage) than the 807. It is the higher 'gain' of the screen grid
that matters here (since a screen grid tube acts as two triodes in
cascade as far as power gain is concerned). The 6146 is actually better
shielded than the 807 and has less lead inductance which helps
stability. In order to avoid neutralization the 807 requires extra
shielding to keep the grid from 'seeing' the plate. Sub mounting the
tube socket below the chassis so the bottom of the plate is even with
the level of the chassis will do the trick. James Millen sold tube
shields for the 807 which were aluminum cans open at both ends with
spade lugs to mount to the chassis. With the 807 sockets mounted to the
chassis and the shields mounted on the chassis, the tops of the cans
would be just below the level of the bottom of the 807 plates.
Recall the AN-ARC5 transmitters? They sub mounted the 1625 tubes so the
plates were just at the level of the chassis, same idea.