Re: Valve frequency multipliers

On Tue, 4 Feb 2025 20:28:15 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

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

On Tue, 04 Feb 2025 09:02:01 -0500, legg <legg@nospam.magma.ca> 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.
 

 
RF design is still in the ancient days of load pulls and Smith charts
and slide rules. I expect that Qspice may change that. Everything
interesting is nonlinear.
 

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

 
Spice is great for modeling mosfets and phemts. Why not tubes?
 

>
Electron transport needs integral equations, so transit time effects aren’t
reducible to a system of ODEs, which is what SPICE knows how to handle.
>
You can phony something up in a restricted range, e.g. the low frequency
limit.
>
Cheers
>
Phil Hobbs

Spice usually works well with its lumped part models. Leads and wire
bonds and PCB traces usually hide the subtleties.

Spice can model thermal systems too, but badly. Thermals really need
3D diffusion models, nasty stuff. A lossy txline is a decent 1D
thermal model, but few real objects are 1D.

It's usually easier to build a thermal thing and play with it, than to
simulate it with some expensive software. I guess if I was designing a
rocket engine or something I'd go to the trouble to simulate it.