Bob wrote:

My newer design approach is to use a switching ring of FETs, but the results
still can't match up to the 7360.
Do you use the fets as passive switches, or do you apply power between
the source/drain? What kind of fets (IE: depletion mode jfets or
enhancement mode mosfets)?

Can you post the 7360 mixer circuit you use somewhere?

BTW these tubes (7360, 6AR8, 6JH8, 6ME8) are sensitive to magnetic
fields and need to be shielded for best results. James Millen used to
make a mu-metal shield that would fit over tubes this size. I would
suspect unshielded tubes could be the reason for the poor results
obtained with some of the color tv versions of these tubes.

Also the 7360 is shown as a tetrode, while the color tv tubes are
pentodes (ie: they have three grids), but grid #2 is grounded and grid
#3 has normal 'screen' voltage applied. Grid #2 is internally connected
to the heater or cathode for these tubes.

"ken scharf" wrote in message
news:RoADk.41384
ken scharf wrote:

What he claimed was that the conversion gain dropped to unity above
that frequency. That doesn't mean it isn't a good mixer at 50mhz.
Diode ring mixers have a unity (or LESS!) conversion gain, yet they
are very good mixers.

The conversion gain should be much greater than unity
for any of those balanced mixers. He was doing
something wrong to write statements like those.

Regarding the DBMs, sure they have some loss,
but the losses basically sets the mixer noise figure.
Add a few dB loss for the the front-end preselector
filtering, and may 8 dB loss for the mixer, followed
by a strong, low noise IF amplifier, and your pretty
much good to go, on the HF bands anyway..

DBMs like to be driven by symmetrical
LO waveforms (square wave is great) and the port
terminations are critical as well. My own experience
with them is that the supporting stages also need good
shielding, filtering and bypassing, they are great
harmonic mixers from DC to light!

I'm sure Bob's H-Ring designs are suberb; I've
pretty stopped playing with mixer circuits after the
DBMs became available well over 20 years ago!

Pete

ken scharf wrote:

Can you post the 7360 mixer circuit you use somewhere?

I'll send you an email tomorrow. I'll have to scan my sketches - as with
all the best projects, the documentation was "informal"!

Bob