) writes:

1n4007 as varactor (freq multiplier) and also Varicap.
That's not really a new thing, or specific to the 1N4007.

Sam Harris, in that first article about parametric amplifiers in
CQ circa 1958, goes into detail of what's required, and then
practically leaves the issue of the varactor to the end. At
the time, they were new, likely expensive, and not easy to get.
Sam had it easy, he worked at Microwave Associates at the time.
So then towards the end of the article where he attends to the
issue of the varactor, he basically says use whatever's available,
try things, and at least practice with those other devices until
you get good at it, at which point it's time for the "real thing".
I have quoted that bit in the past, but I don't know where I've
put the article to get the exact wording.

And ever since then, influenced by his words or maybe independent
thought, the magazines have been full of mention of using whatever's
available as a varactor, the results varying with the diode (or
junction, since some have used part of a transistor) and of course
the application.

And of course, there was one article where the author mentioned a lot
of hum in his six meter synthesizer that used something like a 1N914
for the varactor. He then realizes that the problem was the light
of a nearby lamp getting to the actual diode theough the glass
case of the diode, and hence modulating the VCO that way.

Michael VE2BVW