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Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Hey Dr. Spark,
I bet you could build a modulator for quadZilla that wasn't supper big. Using a buck or SLR topology.
You could probably even do 4 individual supplies to drive the 4 plates! You could force current sharing among the tube this way even with them unmatched!
It would be supper cool to see a supply do this, I can only imagine qaudZilla with AM audio modulation. 50Kw plasma sub woofer hehe
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
Would it be pausible to just modulate the grid of a 833 to create a ramped power envilope? This could be done by using a PWM to tern the tube on for a spesific time period that would be equal to 90 deg or less of the primary tank cycle. Some how the ZCS would have to syncronise with the PWM rising edge so the tube turns on at the right time. The tube is a natural choice to excite a parallel primary tank cycle.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi guys
Well my personal evil plan was to use two pulse tubes in a half bridge configuration to base drive a resonator directly ;) Depending on whether I could beat Steve in making the buck-less QCW work there might be a number of ways to achieve QCW operation with such a setup (including feeding a ramp to screen grid if tubes used are tetrodes) Wondered if those GMI6 tubes would be good for start...
But too many a project already so better keep this dreamware for now...
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
I imagine if you did some kinda grid modulation it would be similar to Steve's delta sigma modulation. As you would be forced to switched at ZCS or with ZVS. So the low freq ripple would be present on the output.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
crazyivan wrote ...
So all Phillip did was feed the plates a ramp current? Just with an inverter? Just curios...
Nope, he used a modulated SLR power supply with a big IGBT brick, as far as I recall. Which I guess is about the same hassle as building a buck converter for a DRSSTC.
I think the first and easiest approach for tubes would be to modulate the tetrode screens. I think it might be possible to use a big inductor in series with power supply to ease the losses on the tube.
Next would probably be sigma-delta QCW. One could use "staccato" modulator to turn the tube on and off while sensing the primary current. So far it's unknown whether this would work.
Finally, there's the possibility of using two big high voltage pulse tubes to feed the resonator base directly. If I ever get a chance to own some awesome pulsed tubes this is how I would build a QCW.. I also think sigma delta would have far more chance of working that way due to 1-order system and naturally slower energy transfer time constant.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
SLR and buck are both noteworthy systems that would work to modulate a coil.
SLR has the advantage of being more efficient because of ZCS and also inherent current limiting. This come at the price of complexity though.
Buck also works but is less efficient and needs a separate current limiting circuit, but they are darn easy to get working and have very few parts.
In the end it's up to preference. Although I like the idea of no modulator and doing all the modulation on the bridge or with the tube screen, I still have doubts about it's piratical application. Mainly the ripple present in this kind of system and also the lower coupling required for it to work properly. But I'm still hopeful!!!
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QCW Documented
