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The 13,56Mhz Vttc

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WaveRider

Mon Nov 26 2007, 10:08AM

Registered Member #29 Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500

Hi Reaching,
You may be able to improve efficiency by using a phase-correction network on the feedback network. This will allow you to (perhaps) make the switching transitions coincide better with zero-plate-voltage (ZVS can work with tubes/valves too)!

Just a thought...because it seemed to work well in my PLL design..

Your coil is beautiful. I want one of those tubes too!!!

Steve Conner

Mon Nov 26 2007, 11:45AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Well, the beauty of tubes is that you don't have to care too much about efficiency! MOSFET Class-E amps have no choice but to run very efficiently, because the losses will destroy the device if it runs inefficiently.

On the other hand, tube circuits are never that efficient to start with, maybe 75% for a fully optimized Class-C amp. The main reason is the on-state voltage drop of the tube, which is a few hundred volts at least.

So tubes are designed to get rid of lots of heat easily, and a little more heat due to bad drive or mistuning isn't going to kill them. When playing with tube circuits, it's OK to forget the math and just mess around.

There are limits though: I once had a tube ham radio rig whose previous owner had managed to melt a hole clean through the plate of the final amplifier tube! :-o In spite of that, it was still working, just a little down on power...

Marko, you can't get tubes in Eastern Europe?! You are kidding, right? Hint: Philips, Valvo, and Unitra (amongst others) made equivalents to the American 4-125, 4-250, 4-400, 3-500 type tubes, but with different part numbers that begin in QB. For example,

Reaching

Mon Nov 26 2007, 05:57PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

yep, even some russian tubes such as the gu81m or gu33b should work fine (pentode and tetrode) the gu33b has less power but will work well too. its not that hard to find big tubes which are not too expensive.

Herr Zapp

Mon Nov 26 2007, 06:59PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Reaching -

Very nice! Could you provide some additional details on your self-made socket?

Also, in the video clip it appears that filament and plate power are being applied simultaneously. You may want to modify your system to allow filament power to be applied first, and permit the filament to pre-heat for at least 10-15 seconds before plate voltage is applied. On larger transmitting tubes with thoriated tungsten filaments, the filaments should always be allowed to come up to full temperature before plate voltage is applied.

For anyone with any interest in VTTC design or operation, Eimac has recently updated their classic technical paper "The Care and Feeding of Power Grid Tubes". This is probably the single most comprehensive source of technical data for high power transmitting tubes, and its six chapters cover every aspect of tube operation, internal construction, circuit design, power supply design, bypassing requirements, operating voltages & currents, tips for maximizing operating life, etc, etc.

This latest update even contains such esoteric information as details of electron flow paths within the tube itself around the grid structure, etc. Although the pictures are primarily of "modern" ceramic-envelope tubes, the information is equally applicable to classic glass-envelope "fire bottles".

This is normally available on the Eimac website, but for some reason I can't find it today.

It is available at

, each of the six chapters being downloadable as separate .pdf documents.

Shan

Reaching

Mon Nov 26 2007, 08:40PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

Wow, thats a great yource and lots of information. . thanks :))

WaveRider

Mon Nov 26 2007, 09:18PM

Registered Member #29 Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500

Shan, your link does not work for me (get 404 error).

Marko

Mon Nov 26 2007, 09:24PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

There is a comma at the end which needs to be removed. It worked for me then.

Herr Zapp

Mon Nov 26 2007, 10:45PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Yes, for the Eimac data delete the final comma in the link URL.

Apparently, when 4HV converted the embedded text URL into the "green arrow" link, it also grabbed the comma.

The URL should be:

Also, here is another interesting article on maximizing the life of really big transmitting tubes, and how detrimental to tube life power cycling the filament is:

Shan

Arcstarter

Sat Jun 21 2008, 08:38PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

I figured i would bring this thread back to life. So anyway... How exactly does this work with no primary? I suppose the voltage from the plate is just sent through a resonator, but i am wondering exactly what does the resonator do?

Spedy

Wed Jun 25 2008, 11:34PM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

I think this works like Telsa's 3-coil resonator, only w/ 1 coil. The coil's base has current switched by the tube at the coil's resonant freq, and the HV builds up because of the resonant action. Does that make sense/is it correct?

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