RadioBanter - SW-3 Questions

Roger D Johnson wrote:
Thanks for all the answers to my questions. It appears
that the remote cutoff 6D6 is the tube of choice.

I'm wondering if the failure of the voltage divider is
a frequent occurance or if someone tried to operate the
receiver with excessive voltage?

Thanks and 73, Roger N1RJ
The 6D6 is a remote cutoff tube and should be used in the rf amp
position. The 6C6 is a sharp cutoff tube and either it or the 6D6 will
work in the detector position. Some people think that the sharp cutoff
types work better as a detector, others think that a remote cutoff tube
might handle strong signals better in the detector position. Try both
and use what works best!

The types 77 is a sharp cutoff tube, and the 78 is a remote cutoff
version. These types are similar to the 6J7G and 6K7G (but with 6 pin
bases instead of octal). They have different shaped bulbs and won't
accept the close fit shields that fit the 6D6/6C6 tubes
but might fit the larger National shields. They will work as well as
the 6C6/6D6 tubes (different inter-electrode capacitance and gm but not
enough to make a difference in this circuit). Also the 6U7G is the
octal equal to the 6D6, the 6C6 has no octal equal. (not that you were
thinking of rewiring to octal sockets....)

As for the voltage divider resistor, the schematics I found on the web
show the total resistance was 12k, but I don't know what the taps were
at. You could get a 10-15K 20w adjustable power resistor with an extra
tap and make up your own. Looks like the lower tap would be at 30% and
the upper tap at 60% based on the fact that the lower tap feeds the
regen control (max voltage about 50) and the upper tap feeds the screen
grid of the rf tube (about 100v) the set ran at about 150v total.
So you probably would get away with 3 5K ohm resistors in series.....