Re: [Qucs-help] Q: Vacuum tube schematic symbols & SPICE models

[Gene H. <ghe...@sh...>]

On Thursday 23 January 2020 18:32:20 Dr. David Kirkby wrote:

> On Thu, 23 Jan 2020 at 19:24, Federico Miyara
> <fm...@fc...>
>
> wrote:
> > Gregg,
> >
> > Vacuum tubes are by no means a fossile specimen buried in technology
> > ancient history. Most electric guitar players will die for a good
> > tube preamplifier. It may be arguable, but these are the facts.
> >
> > Federico Miyara
>
> At the high power end they win too. You can get a couple of MW
> continuously out of a tube amp. I suspect that for short pulses 1 GW
> is practical.
>
> I used to work at Marconi. On the same site was E2V which was part of
> the Marconi group of companies. Before they could run some of their
> big valves, they had to get permission from the National grid, because
> the power they used was so great. I suspect that one tube would take
> close to 4 MW of power.

As a retired broadcast Chief Engineer, with extended time in the care and 
feeding of klystrons back in their heyday, since I became an occasional 
user of Qucs, I have often wondered if there were ways to synthesize 
their operation in Qucs?  Those would have to have a way to plug in the 
effects of E=mv2 from Einsteins theory as that is the only way to 
explain the waveform distortions they introduce to the output signal, 
and which we had only very rudimentary means to correct by 
pre-distortions.  The Ward Equalizer was king, but had no means to 
correct for its variable group delays due to the instantaneous power 
levels.

Simply put, its electrical length varied with the instant power level due 
to the non-linear effect of not being able to speed the beam up by the 
same velocity change to match the slowdown on the other half cycle of 
the sine wave input.  Said another way, at 20kv for beam voltage, the 
electrons in the beam were moving at speeds where E=mv2 could be 
observed. Because they got more mass when sped up they put that energy 
into their mass so they didn't speed up as much, and lost mass when 
slowed down so the same energy slowed them easier, the beam appeared to 
get longer when that variation was at the high power end, sync tip power 
in a ancient mary (VSBF) tv transmitter by 100ns or more.

Better ways to make shorter tubes were invented at about the same time, 
reducing that distortion at about the same time ways to pre-distort in 
the time domain AND the dc power level were developed. These new tubes, 
called klystrodes were a bit cheaper than the $100,000+ for a klystron, 
and considerably more efficient, so in just 5 years or so, the reduced 
power bills bought most UHF broadcasters a new transmitter with the 
savings. Quite a few couldn't finance it and went dark too.  That was 
all 40+ years ago. Yeah, now I'm an old man, and my parts list is 
beginning to look like Lee Majors. But theres been a heck of a lot of 
been there and done thats in my time here. 

Cheers, Gene Heskett
-- 
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