Re: Valve frequency multipliers

On Tue, 4 Feb 2025 20:11:56 +0200, Tauno Voipio
<tauno.voipio@notused.fi.invalid> wrote:

On 4.2.2025 16.02, legg wrote:

On Sat, 01 Feb 2025 07:23:57 -0800, john larkin <JL@gct.com> wrote:
 

On Sat, 1 Feb 2025 10:50:22 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
>

john larkin <jl@glen--canyon.com> wrote:
>

On Fri, 31 Jan 2025 23:50:56 +0000, Cursitor Doom <cd@notformail.com>
wrote:

[...]
>

    Operating Point:
        Grid Voltage: Adjusting the grid voltage to operate closer to
cutoff can increase harmonic distortion since the tube's response
becomes more non-linear near cutoff.

>
Operate it deep in cutoff, off most of the time. A high amplitude
drive and grid-leak bias would be good.

>
That is exactly what I am doing and it doesn't appear to be working.
With 100v on the anode,  15 Mc/s at 25v pk/pk on the grid and a 22k grid
leak, the peak current for one triode of an ECC91 is around 20 - 30 mA
at the positive peak of the grid swing.  The average anode current is
around 2.5 mA, so the conduction period is about 10%.
>
A 75 Mc/s parallel-tuned circuit in the anode circuit is giving so
little drive to the following stage that I can't see any change in the
average grid voltage of that stage caused by the drive.

>
Spice it!
>
LT Spice has tube models.

 
If Spice was of any use in RF ham gear, the amateur radio guys
would have been all over it three decades ago.
 
I've modeled known-good valve power cctry only as a curiosity, to
see if spice could come anywhere close to practical results.
Curiously the nowhere-near-common valves used already had models,
so I'm pretty sure somebody else had already made a run at the
identical application. (Tek HV oscillator).
 
RL

>
>
I used, but well over half a century after the target device was built.
>
I designed and built a novice class CW transmitter in spring 1969. It
was used by several novices to get their required experience, and stored
after the novice class requirements were changed decades later. The
transmitter was found when the attic of my parents was cleaned.
>
The cleaning was done in 2020, at the worst COVID block-out time.
To do something useful, I created a description of the transmitter in
LaTeX, as an exercise. I used LTspice to draw the schematics, and as
a side product, a working model of the transmitter got born.
>
I had to create plenty of components, e.g. all tubes (EF94/6AU6,
EL83/6CK6, EL500/6GB5 and OA2/150C2). With extensive Internet search,
the matching Spice models were found, mostly from HiFi enthusiast
pages.
>
When running the models, I noticed that a real-world crystal model is
too slow to start, so I had to change it to lower Q, so that the solver
did not grow tired to start up. The simulated results matched quite well
with the built device, despite that in a transmitter, the tubes are
working well outside of the normal HiFi biasing range.

Spice is really good at operating outside normal ranges.

Some might call that an advantage.

RL