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From: john larkin <JL@gct.com>
Newsgroups: sci.electronics.design
Subject: Re: Valve frequency multipliers
Date: Sat, 01 Feb 2025 15:42:56 -0800
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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.