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Is the GI23B tube good for VTTC?

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grzesiek94

Wed May 12 2010, 01:36PM

Registered Member #2854 Joined: Wed May 12 2010, 01:18PM
Location:
Posts: 8

Hello,

I am going to build a small VTTC powered by the microwave oven transformer, and I wonder what tube I should use. I could buy a GI23B triode, which has a 300W output power, but I don't know much about vacuum tubes. Can I use this tube for the VTTC? I have never seen a VTTC with this tube.

Datasheet of this tube is here.

I've got a one more question - is it possible to use a Staccato controller with this small tube?

Sorry for my English, I live in Poland :P

Arcstarter

Wed May 12 2010, 06:32PM

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

Yes, that would be a very nice tube for a medium power vttc. It seems to have a very high anude voltage, apparently 14kv max... It also has admirably low heater current, which that is always a plus. And any tube that will work for a vttc can be used with staccato.

Be careful though, i am willing to bet this tube has an incredibly fragile filament and grids. If you so much as bump it while hot, it could break the filament. Be careful!

Dr. Dark Current

Wed May 12 2010, 06:42PM

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

I think it should work, it seems to be for pulse duty however. To what Arcstarter said I'll add, be careful with the grid driving power, the "external anode" tubes need less power and you might as well melt the grid if you just put the tube in the place of an internal anode one.
And of course you must cool the tube with a fan, but I guess you already know that

grzesiek94

Wed May 12 2010, 08:35PM

Registered Member #2854 Joined: Wed May 12 2010, 01:18PM
Location:
Posts: 8

Thank you for reply.

I'll buy this tube. As you are writing this tube is fragile, so what value of the resistors and capacitators I should use with this tube? I am going to use a Class-C Armstrong oscillator like this used in Steve Ward's VTTCs with a VTTC level shifter to increase anode voltage.

So what modifications I should do to this schematic?

I don't want to burn this lamp because it is difficult to get.

Herr Zapp

Thu May 13 2010, 04:58AM

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

Arcstarter wrote:

" i am willing to bet this tube has an incredibly fragile filament and grids".

What would lead you to make this assumption? The datasheet in the link provided by grzesiek94 shows the tube is rated to withstand a single shock event of 150 Gs, multiple impacts of 75 Gs, and 10Gs continuous vibration between 5 and 1,000 Hz.

Doesn't sound "incredibly fragile" to me ....... remember, this tube was designed to continuously switch 40,000 watt pulses in a military application.

Regards,
Herr Zapp

grzesiek94

Thu May 13 2010, 06:29AM

Registered Member #2854 Joined: Wed May 12 2010, 01:18PM
Location:
Posts: 8

Uh, I'm confused now... So I may use this tube like the "normal" one?

This tube is directly or indirectly heated? In datashet is written that tube is indirectly heated, but symbol looks like tha directly heated tube.

Dr. Dark Current

Thu May 13 2010, 07:51AM

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

I would use something like 3x higher value of the "grid leak" resistor...

Steve Conner

Thu May 13 2010, 08:43AM

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

Mechanically fragile and electrically fragile are two different things.

RTFDS, it will give you a value for maximum allowable grid current and/or dissipation. I just looked and it says 25 watts, seems plenty tough to me.

There are other similar Russian triodes, the GI-7B is very popular with hams and has a whole website devoted to it.

grzesiek94

Thu May 13 2010, 01:36PM

Registered Member #2854 Joined: Wed May 12 2010, 01:18PM
Location:
Posts: 8

Finally, buy this lamp or not?

If so, what value of grid leak resistor and capacitor I should use?

At least, it's a Russian military triode. I've seen GU50 pentodes (max anode voltage 1200V) powered by a 2100V from MOT in VTTC configuration. And it somehow works.

How many microwave HV capacitors I should connect in parallel for a voltage doubler used to power this tube?

Herr Zapp

Thu May 13 2010, 08:12PM

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

grzesiek94 wrote:

"This tube is directly or indirectly heated? In datashet is written that tube is indirectly heated, but symbol looks like tha directly heated tube."

No, the filament symbology corresponds with the "indirectly heated" description in the datasheet. The filament is shown linked to the tube's filament pins, while the indirectly heated cathode is shown as a small arc-shaped line just above the filament.

If the price is reasonable, buy the tube and build your coil. The optimum values for grid leak resistor, feedback coil location & turns count, etc. can only be found by experimentation.

If you've not previously worked with high voltage apparatus, be aware that your voltage-doubled microwave oven power supply has the potential to be instantly fatal. Use bleeder resistors across each HV capacitor, and everytime you turn the power off, manually discharge the caps with a shorting jumper before touching anything.

Regards,
Herr Zapp

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