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Which is easier?building a good SSTC or building a good VTTC?

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hsieh

Mon Oct 24 2011, 08:29AM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

I build several SSTCs several months ago.But I only get small sparks and my MOSFET gets very hot at low power.I checked everything I could and cannot find out whats wrong.I also build a VTTC using two 811 that runs on halfwave rectified MOT and get 15cm sparks(but the plate turn orange after about 30 seconds)

I am now considering to build several TC and I find someone selling high power tubes at a very low price.Since the circuit of a VTTC seems simpler and has fewer components,is it easier to build a good VTTC than build a good SSTC?(SGTC is not an option)

Thanks

Dr. Dark Current

Mon Oct 24 2011, 09:55AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

The VTTC is indeed easier, but usually requires more expensive components.

christensenda

Mon Oct 24 2011, 09:56AM

Registered Member #3062 Joined: Wed Aug 04 2010, 02:07AM
Location:
Posts: 22

As far as complexity goes building a VTTC would probably be considered easier than most SSTCs. I have been considering lately building either a 4-250A I was told to expect somewhere from 10-12" for a well built 4-250A or that a 833A VTTC could achieve 18-24" inches depending on whether or not you plan on running it in Staccato mode which would add to the complexity but the run times for your tube should be much more significant.

Mads Barnkob

Mon Oct 24 2011, 11:13AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

I build my first VTTC before my first SSTC. With a oscilloscope the SSTC is by far easier to build when you understand the concept of a simple interupter driving a half bridge of switches.

A VTTC can be much trickier to get to work properly as you have to experiment A LOT with primary taps to tune it, not always that easy as many turns are needed, people often resolve to use wire, adding tap points to that is a drag. The feedback coil is a whole story to place it correctly and find a proper feedback RC value that drives the valves within reason.

I would advice for a SSTC as the first if you understand electronics good and a VTTC if you are more into "lets move this part and see what happends" science.

Patric

Mon Oct 24 2011, 01:43PM

Registered Member #2899 Joined: Wed Jun 02 2010, 06:31PM
Location: Deinze, Belgium
Posts: 255

If something goes wrong, then you see the VTTC dye, and you can (most of the time) save it. A SSTC is 'gone' before you know it.

Daniel Kramnik

Wed Oct 26 2011, 03:52AM

Registered Member #3885 Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94

Patric wrote ...

If something goes wrong, then you see the VTTC dye, and you can (most of the time) save it. A SSTC is 'gone' before you know it.

Not if you're carefully monitoring temperature and primary current - also, a "dead" SSTC means 5 minutes of replacing $4 transistors while a damaged VTTC means you'll either have to settle with poorer performance (if you damage your tube) or wait weeks for a new $100+ tube to come.

I can see the value in building a small VTTC as a starter coil (as I did), but I can't justify the expense of a large VTTC when there are so many better options available.

hsieh

Wed Oct 26 2011, 03:45PM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

I found someone selling 4CX250 at about 17USD each at a local website and someone selling a giant tube(1.5KW plate dissipation) for induction heater at about 40USD.

I also found a lot of free MOSFET in the trash can at a school lab.

If cost is not a very important consideration,which one is easier to build? which one is safer?

Inducktion

Wed Oct 26 2011, 06:39PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Well, considering a VTTC has high voltage on both sides (since tubes use a good amount of electrons :P ) A VTTC I would think be slightly less safe than a STTC. (since, a SSTC just has logic and a bus supply) But, they're both Tesla coils, and both put out High voltage high frequency electricity. Not something you really want to be touched with. RF burns hurt a lot from my understanding.

Dr. Dark Current

Wed Oct 26 2011, 07:54PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

The SSTC is a lot safer - the plate supplies for tubes are often deadly (and not far away in parameters from an electric chair).

Mads Barnkob

Wed Oct 26 2011, 08:09PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

One topology isn't safer than the other, it all depends on how you go about working with electronics. For all we know you could be safe working with 2000 Volt, but choke to death on a 1.5 Volt battery...

That being said, my first VTTC had a 3000 VDC plate supply and the SSTC had 320 VDC, I know which one I would rather get shocked of. None of them!

I will still suggest building a SSTC as its a straight forward design as used in so many other daily used electronic devices. You have a logic part you can easily debug with a oscilloscope. You are not dependant on tuning your primary circuit for resonance, you just use a feedback to the logic circuit.

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