Bill Turner wrote:

On Mon, 17 Nov 2003 10:23:42 +0100, Claude Frantz
wrote:

Where can I find good information about the design of frequency
multipliers using vacuum tubes ?

Claude

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ARRL handbooks from the '50s had numerous articles and examples of
frequency multipliers using tubes, since that was state of the art back
then. Basically, you just overdrive the grid in order to create severe
distortion, then tune the plate tank to the desired harmonic. It's
normally done at a low power level because the process is relatively
inefficient. If memory serves me right, getting efficiencies of 10-20%
was considered pretty good when using the second or third harmonic.
When higher harmonics were needed, two or more multiplier stages were
commonly used.

A typical six-meter rig of the '50s would use an 8.334 MHz crystal or
VFO oscillator, tripling that to 25 MHz and then doubling that to 50
MHz. Also common was to operate an 8.334 crystal on its third overtone
of 25 MHz and then doubling that to 50 MHz.

Ahhhh, the good 'ol days. :-)

Once the PLL became inexpensive, frequency multipliers became a thing of
the past. But they do get the job done.

--
Bill, W6WRT

And then there was the sub-harmonig generator with zero plate volts,
power going in to the plate and power out of the grid.
Not a joke; saw it done at Sylvania in the late 60s.
Used a tetrode, 2nd grid had about 30V on it to act as a plate in
Hartley oscillator configuration.
Set to not oscillate with zero signal, would "slowly" ring up on
application of RF; like someone sitting on a swing and then starting it
by mere pumping.