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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Steve McConner wrote ...
I think the simplest oscillator you could make with these would be a shunt-fed Tesla coil. You'd connect the tube anode to the top of the resonator, and feed something like 25kV DC (from TV flybacks?) to the base. To get voltage gain, you could tap the anode down from the top, maybe halfway up the resonator or something. Grids could be driven from a feedback coil, like in a normal VTTC.
It would probably be limited to 10s or 100s of kHz in order to keep the Z0 of the resonator high enough. Connecting 10 or 20 tubes in parallel would help of course
I might just give that a try, Steve. I have the EHT on tap, so only have the valves to tinker about with.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
If you do what Steve is suggesting, try and take measurements of the output vs. frequency. I'm interested in how much it will vary over the sweep. You should see a lot of variance and an enormous increase/decrease around the resonance of the inductor.
That was why I was asking about how stable you want the output.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
I don't think you understood what I was getting at. I'm trying to say the Bode plot of the output response will have quite a bit of slope to it and I'm interested in what that Bode plot looks like, especially at higher power levels.
You should get some unexpected results as the frequency and SWR changes near the resonance point and near the lower and upper cutoff frequencies, I'm just curious what its curve will look like.
See, I'm trying to get an amplifier going too, but my s#$t just doesn't work well, ;( , so I'm going to play with a couple of tube things soon.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Hazmatt, I think you're getting confused between an oscillator and a broadband amplifier. Harry wants to make an oscillator, as the first post states.
If you tried to use his proposed oscillator as an amplifier, of course it would show a huge peak in gain at its resonant frequency. That's how you make an oscillator: you take a narrowband tuned amplifier and feed some of its output back to its input. The more sharply tuned the amp is, the better the oscillator will be.
This is related to Murphy's law of electronics: "Amplifiers oscillate and oscillators don't." The reason is that they're both the same thing. The amplifier malfunctions because of too much feedback, and the oscillator refuses to work because of a lack of feedback.
PS, when manana isn't enough, there's always "la proxima semana". When your boss needs something done "ayer", hide until he goes away.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
I'm looking forward to the plots.
Steve, unless you employ active feedback and an output detector like a constant amplitude signal generator, the output amplitude will still vary quite a bit and that's what I'd like to see on the plot, the amount of variance.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Well, Hazmatt, if you asked me to guess, I'd guess that the output will fall with increasing frequency, with odd spikes and troughs here and there caused by unwanted resonances, sudden Q loss effects, parasitics, harmonics, jitter, corona noise, and so on. But we shall have to wait and see...
I don't have any very accurate means of measuring HF RF voltages of >20kV so whatever I come up with will be an approximation.
And don't go expecting anything even vaguely digital from me! Drop by drop every cell of my body and brain is being replaced by calcite, a Living Fossil of the Thermionic Age
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
HAHAHHAHAH. Harry, I do frequency response plots data point by data point as well. I have an analyzer sitting behind me right now but the bugger refuses to plot or talk (GPIB). So I will devise my own 2 port analyzer on a uC and have it plot for me.
I know where you're coming from. I'm considering building a massive class C amp right now for my project because I'm getting fed up with the transistors I have on hand. I need to talk to Motorola because I'm not an RF engineer.
I hear ya...hahahhaha.... 20KVAC ADC would be nice. oh boy. So much to do... such little time.
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EHT HF/VHF Triode VFO Concept
