Yuri Blanarovich ) writes:
Back from good old tube days, cascoded triode RF preamps were good for high
gain, stability and low noise.

Anything out there in transistorised version, or there is there better stuff
available? Looking mainly for preamps on HF to be used with low gain antennas,
like small loops or beverages.

Yuri, K3BU.us

You definitely saw them in the early days. The one that comes immediately to
mind was a cheap preamp described in Ham Radio in the early seventies,
and was available as a cheap kit from Hamtronics.

I think there were some shown with bipolars, but I can't dredge up
any specific memories at the moment.

It was obviously a transitional thing, since you're right, one doesn't
see solid state cascodes very often. I have no idea if they were
used decades ago because it worked around limitations of early solid
state devices, or if it just seemed to be the thing to do since they
had been common in tube circuits.

The author of that Ham Radio article (actually, there were two, and he
used cascode FET amplifiers in various projects described later), I think
his name was Jerry Voigt, had grumlbed about the then relatively new
dual-gate MOSFETs, but in a followup letter he admitted than a dual-gate
MOSFET was basically a cascode device.

If there was an advantage to be using cascode circuits today, then
you'd be seeing them.

A lot has changed. Bipolars came in, and they couldn't handle strong
signals well. The JFET came along, and it was seen as the device
to use for best performance. The MOSFET came along, and again there
was a switch. Sort of simultaneously with MOSFETs, but not really adopted
till later, bipolars started being capable of low noise and strong signal
handling. MOSFETs are now rare for receiving applications. Gasfets came
along and they seem to be be the thing for low noise RF amplification.

Michael VE2BVW