Re: Valve frequency multipliers

john larkin <JL@gct.com> wrote:

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.

I don't know the parameters that I need for this job, the valve manuals
only publish static figures and some basic curves.  Finding out things
like the gm of an EF91 when the signal is applied to G2 or G3 is almost
impossible as an academic exercise, it is quicker to solder up a test
rig and get the answer by experiment.

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk