So if the Gilbert cell is simply a differential pair on top of a
constant current source, and you are advocating only the differential
pair, then I suppose you are advocating the equivalent of a Gilbert
cell with no current source.

Someone had mentioned that I should be using a silicon diode mixer, but that's
not the point... I want my designs to be all battery tubes (plate 25-60
volt), so that the gear can be portable and also withstand electromagnetic
pulse.

The 7360 and 6AR8 require too much plate voltage.

Now from what I understand, the passive double balanced mixer has the best
port isolation, which makes it superior to the Gilbert cell for avoiding
spurs. On the other hand, the Gilbert cell has conversion gain but is more
vulnerable to spurs. So I wonder if the better answer is to build a DBM in
glass, or the differential pair?

The Eternal Squire




(Avery Fineman) wrote in message ...
In article ,
(The Eternal Squire) writes:

Has anyone ever implemented a gilbert cell mixer using valves instead
of FETs?
I'm considering this instead of using the increasingly rare and costly
heptode mixer.

To do this, one needs a minimum of three triodes, the top pair
being (essentially) a differential amplifier, the bottom being a
configured constant-current source replacing a moderately-
high common cathode resistor for the differential pair.

That's a LOT of circuit work where a single dual triode could
(and has) work just as well. Connect it as a differential pair
and put the signal in one side, the LO in the other.

Any valve that runs its control grid into the positive region is
going to be operating in a non-linear region and will therefore
"mix" well enough to do some heterodyning.

The name "Gilbert cell" got there in later integrated circuit
times to describe a particular arrangement of BJT junctions
to do mixing or AGC actions. Valve circuitry had other
names and worked for decades as mixers quite will without
fancy names. :-)