[HBR] Mixers

[Walt Hutchens]

Donald said:

> My LONG SLOW project is based on the Collins r392.  It is now in it's 3rd
> iteration--the final one-I hope!
> In the first and second versions I used a conventional heptode converter-no
> problems, so I will probably use it in the final version......but Walt's
> dual triode looks like something I would like to try.
> -----maybe a 12u7 ?  I think Walt said plates and cathodes were in parallel
> with LO to one grid and signal to the other....
> ---I am using 26 volt tubes (R392), so I would have only 26 volts on the
> plates.

While a 12AU7 will work as an oscillator with 26V on the plates I don't know
what sort of mixer it would make.   The gain of a triode as an amplifier
goes down pretty fast at low plate voltages.   And the 12AU7 is used in this
mixer circuit mainly when large signal handling is required: In a
transmitter or perhaps as a second mixer in a double conversion receiver.

At 26 plate volts I'd go with what has worked before.

Toroids are a very good way to go for compact high Q work.   Despite some
sources saying you can't wind to an exact inductance, my experience is the
same as yours: There's enough leakage flux that turns spacing can be used to
make fine adjustments.

Walt
KJ4KV