Re: Valve frequency multipliers

On Sat, 1 Feb 2025 21:53:43 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:

john larkin <JL@gct.com> wrote:
>

On Sat, 1 Feb 2025 17:08:20 +0000, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:
 

On 01/02/2025 15:40, Liz Tuddenham wrote:

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.

 
...but I haven't got Spice.

>
LT Spice is free and works very well indeed. And you can't beat the
price. No idea how good it's valve models are but I bet they do exist.

 
It has a triode, a tetrode, and a pentode. I haven't tried them, but
there are a zillion YouTube videos about LT Spice.

>
I'm afraid that doesn't sound very promising.  A triode could be
anything from a water-cooled UHF transmitting valve to a PX4 to a
1.5-volt battery-powered miniature audio type.  At VHF all sorts of
things come into play, including the material of the valveholder.

Tubes have model files, and you can adjust various parameters.

>
For me to find a version of Spice that works on my computer under OS8.6,
then learn to use it well enough to get any useable results would take
years - with almost no chance of the outcome working any better than if
I had guessed at the component values to start with.