Re: Valve frequency multipliers

On Fri, 31 Jan 2025 13:51:25 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:

I am trying to use a 15 Mc/s crystal oscillator to generate a 150 Mc/s
signal, the obvious multiplication ratios are x5 and x2.   The 150 Mc/s
has to be distributed to two other units by a 120-ohm screened cable.
>
The whole thing must be done with the minimum number of valves and no
semiconductors.

Why?

 The Colpitts-derived xtal oscillator is an EF91 and the

multiplier stage(s) can be either another EF91 or an ECC91. 

Why not use a 150 MHz xtal?

>
I have tried picking the x5 signal (75 Mc/s) off the anode of the
oscillator with a tuned circuit but can only get a couple of volts
pk/pk.  This isn't enough to drive the ECC91, which I  had hoped could
be used as a 'push-push' doubler, it also won't drive an EF91 over
enough of the curved portion of its characteristic to give sufficient
frequency-doubled signal.
>
Alternatively, I have tried using a parallel-tuned circuit at 15 Mc/s in
the anode of the xtal oscillator to drive one of the triodes of the
ECC91 which can then act as the multiplier.  There is a whopping great
15 Mc/s signal going into the grid of the triode (about 25v pk/pk) and,
with the cathode earthed, this develops enough grid-leak bias that the
valve is conducting anode pulses of over 20 mA about 10% of the time.
>
I would have thought that under those conditions the triode would have
given a large signal at 75 Mc/s in an anode circuit tuned to that
frequency - but it doesn't appear to.  I can't use the triodes as
straight earthed-cathode amplifiers at those frequencies because of the
Miller capacitance effect, but they should be perfectly satisfactory as
multipliers where the grid and anode circuits are  tuned to different
frequencies.
>
Does anyone know how to determine the optimum conditions for generating
the 5th and 2nd harmionics in valves?

One dual triode could make two injection-locked oscillators.