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Small dirty VTTC from scratch done in one hour

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RayeR

Fri Feb 20 2009, 11:21PM

Registered Member #333 Joined: Mon Mar 20 2006, 06:02PM
Location: Czech Republic
Posts: 45

Hi,
I just got LD2 tube - a small transmitting triode with Pa 12W made by german Wehrmacht (I guess it was used in aircraft transceivers) from my colleague at work. I wanted to demonstrate to colleagues what such tube can do so I decided to quickly make a small VTTC from scratch. I also wanted to try out the bottom feeding method directly from tube's plate. I took a glass and wound ~52 turns of 0.35mm wire from some old XFMR as TC resonator. Then I made 7 turns feedback coil wounded on cylindric from, fixed by hot glue and then put down from the form. I put together minimalistic circuit with tube, mains rectifier, RF blocking choke and feedback and resonator coil. First I turned it on via 60W bulb as current limiter. I need to play with feedback little bit. It seems that circuit oscillates better with weak coupling than with tight coupling - this is the reason why feedback coil is under resonator and little bit side away from center. When I found optimal FB position I thow bulb away and connect it directly. I was quite surptised that such poor resonator wit few, not perfectly wounded turns, can fire up about 1cm sparks. It can light up fluorescent tubes around 20cm distance and make plasmaglobe from a bulb when connected directly to resonator output. It is operating at ~3,7MHz. Filter cap is low so modulation shape is nearly half sine wave. It can operate 15 minutes without failure and overheating :)

I well know that this circuit is simple dirty and dangerous because of direct connection to mains so it is not good idea to touch the sparks but for demosntration I did it, we have well insulated floor :) So take it just like spontaneous technical curiosity not a recommended guide.

SCHEMA

Proud Mary

Fri Feb 20 2009, 11:57PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Here is the LD2 data sheet for anyone who is interested:

Tom540

Sat Feb 21 2009, 12:06AM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617

That's cool and really simple. I also couldn't help but notice that awesome speaker box you made.

Weston

Sat Feb 21 2009, 12:36AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

What American tubes would this work with?

Arcstarter

Sat Feb 21 2009, 12:45AM

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

Weston wrote ...

What American tubes would this work with?

Pretty much any triode. This thing requires an insanely small amount of current, his vacuum tube is only made for 30 ma :). I think, cannot read different languages good. I shall try this with an 811A and higher voltage source, higher freq coil, and stuff...

RayeR

Sat Feb 21 2009, 02:00AM

Registered Member #333 Joined: Mon Mar 20 2006, 06:02PM
Location: Czech Republic
Posts: 45

BTW did someone tried direct bottom feeding with some real power tube at higher voltages? What results can I expect compared to classic VTTC with parallel resonant primary circuit? And is there some equation to roughly calculate impedance of bottom feeded resonator? I guess it would be greater than typical tube plate impedance so it's usually used at high frequecnies where the impedance should be lower.

>Tom540
yeah cartoon "woofer" but it's usable for sometimes watching youtube movies :)

Arcstarter

Sat Feb 21 2009, 02:13AM

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

RayeR wrote ...

BTW did someone tried direct bottom feeding with some real power tube at higher voltages? What results can I expect compared to classic VTTC with parallel resonant primary circuit? And is there some equation to roughly calculate impedance of bottom feeded resonator? I guess it would be greater than typical tube plate impedance so it's usually used at high frequecnies where the impedance should be lower.

>Tom540
yeah cartoon "woofer" but it's usable for sometimes watching youtube movies :)

(large tube)

(small tube)

(awesome tube with very powerful arcs, came from a new thread on here)

These are awesome, i am making one right now.

RayeR

Sat Feb 21 2009, 03:05AM

Registered Member #333 Joined: Mon Mar 20 2006, 06:02PM
Location: Czech Republic
Posts: 45

Arcstarter wrote ...

(large tube)

(small tube)

(awesome tube with very powerful arcs, came from a new thread on here)

These are awesome, i am making one right now.

Huh, all this looks like lighters rather than TC :)
And did it someone tried with classic big secondaray, say 200kHz or it has too bad performance. I'll try myself on my existing TCs...

Arcstarter

Sat Feb 21 2009, 04:50AM

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

Well, i tried it with an 811A with a mot as power supply. It worked, but the tube is cherry redin about 3 seconds :'(. I knew that was going to happen though. It is ATM unrectified, and the sparks reach out about 1 inch. The ground arcs are incredibly thick and hot, if i could draw an arc for a second, it would melt pretty much anything i'm sure. When i get it running good, i shall start a project thread :P.

Weston

Sat Feb 21 2009, 05:10AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

Could I use a 12au7?

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