GU5B VTTC project / Projects / Forums

Forums

4hv.org :: Forums :: Projects

« Previous topic | Next topic »

GU5B VTTC project

previous 1 2 3 4 next

Move Thread

LAN_403

vasil

Wed Jul 22 2009, 05:50AM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

Yes, I keep a little free space on the wood plate with the RC network for a staccato circuit, so it can be added later.

vasil

Sat Jul 25 2009, 06:49PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

FIRST LIGHT

-40 primary turns
-21 feedback turns
-1.46 nF @ 18 kV primary cap
-1.36 nF grid cap
-11 nF filer cap
-5 microF doubler cap

The final setup:

Primary cap

Coils:

First light: 60 cm sparks to a grounded copper rod.

http://www.youtube.com/watch?v=wUbfZzKTpiw&feature=channel_page

I am using 2200 V output MOTs in my doubler. I will try to find some 2500 V output ones, so maibe I will have a few inches more in spark lenght.

brtaman

Sat Jul 25 2009, 07:27PM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Amazing coil, vasil!

Those are some very nice sparks. Do you plan on adding staccato? How much more do you think you can squeeze out of that monster tube?! Gonna start searching the Internets for a GU5B. :O

Again great work, your project is really coming together.

vasil

Sat Jul 25 2009, 07:32PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

No staccato yet, have to see how much can get out without it.
I have already a plan to modify the power source to get more juice.

Dr. H.

Sat Jul 25 2009, 09:57PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Good day Vasil

nice looking coil. Congrads on first light. :)

Looking forward to breaking the 1m barier. With that tube you shoud be able to pull double the size of those streamers. Start tinkering with the feedback coil and the primary circuit.

Keep up the good work sir.
Cheers.

vasil

Sun Jul 26 2009, 06:53AM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

Are you sure?

For, let say 3600 W on plate, the Freau formula predicts only 0.5 * sqrt (3600) = 30 inches sparks for a well balanced system.
Maibe I can break 1 m but it would be a risk for the tube.

Steve Conner

Sun Jul 26 2009, 10:01AM

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

Nice work Vasil! :)

Spark length is determined by peak power, but plate dissipation is determined by average power. So you can get longer sparks without damaging the tube, by increasing the peak power without increasing the average.

This is what the staccato circuit is for. If you set your staccato to every other cycle (25Hz PRF) you can now retune your tank circuit for twice the RF power. Or increase the HT voltage by a factor of 1.4, or whatever.

Given the size of the tube you're using, I think the power supply would burn out before the tube does! :O Just watch out for overheating of the control grid. You can't easily see it glowing because of the metal envelope and bright filament nearby, so a grid current meter would be a really good idea.

Dr. H.

Sun Jul 26 2009, 05:26PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Good day Vasil

YES - I am absolutely sure - if you look at my thread about the double GMI-7 coil you will see that I am using two MOTs in series, and the plate dissipation rating for each of the tubes is like 180W and I am hiting the 1m (40inch) ceiling without any problems (and the system is still not tuned because have problems with flashovers.) And also have in mind - I do not use staccato (for now that is).

Cheers Dr. H.

vasil

Sun Jul 26 2009, 05:55PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

Thanx

From datasheet I can not know a few things:

http://www.tubes.ru/techinfo/Broadcast/gu-5b.html

What is the max power dissiaption on the grid? The max grid current?
How much is the peak voltage supported by this tube? If I increase slowly the plate voltage are the eventually breakdowens fatal for the tube?
Where do I have to put the A-meter (on the grid or between RC network and negative pole? Have to use a DC A-meter or AC one? (didnt use anything like that before).

This is the actual power source schema (4 MOTs in phase and doubled):

I will modify this to get twice voltage:

I would not go above 7 kV (at 7.2 kV an 833 suffered breakdown in Freau VTTC magnifier) though for safety reasons for the tube. Thats under 140 V on variac from my calculations.

Steve Conner

Sun Jul 26 2009, 08:30PM

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

Dr. H: If I remember right GMI-7 tubes are designed for extremely high pulse currents in radar modulators. They have huge oxide-coated cathodes that can deliver several amps of current. So it's not surprising that they can generate high peak RF power and colossal sparks. The peak power capability of Vasil's tube might well be less, even if the average power capability is greater.

As for all those questions, we'll need to hope that someone who reads Russian comes along. :( I do know that the grid current meter should be DC, and you insert it in series with the grid leak resistor at the grounded end.

previous 1 2 3 4 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob