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Kolas

Wed Jun 14 2006, 02:39PM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

Oh, yes, the water cooling system works, isolation though, is still a porblem.

Which leads into my next question. The plate is cooled on this tube. How would I water cool the tube but not have conductance from my plate to what is obviously going to be a much lower potnetial pump?

Yes, I feel the armstrong circuit MIGHt work but I felt that squarewave amplification would have higher output then the sine wave amplification that the armstrong circuit uses.

thoughs?

Kolas

Steve Conner

Wed Jun 14 2006, 03:24PM

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

The usual way of doing that is with about 20 feet of rubber hose. The water still does conduct somewhat, but the long hose reduces the leakage current to an OK level.

The 6696 is water and forced air cooled. By that, I think they mean that the seal area gets dangerously hot even with the water cooling active, so it also needs an air blast directed on the seals and contact areas. I guess that might not be a problem at reduced power levels. The datasheet for the original Machlett tube mentions this.

If you look at the tube characteristic on page 5, you can see that it's possible to get several amps of plate current before the thing even starts drawing any grid current at all.

Square wave drive might well be more efficient than sine wave drive. But a properly adjusted Armstrong oscillator type of circuit will operate in Class-C where the plate current is starting to look somewhat like a square wave anyway.

Kolas

Wed Jun 14 2006, 07:01PM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

yeah i've been using that data sheet for the duration of the planning process, for the 6696a, it mentions nothing about air cooling, the 6697 it IS a air cooled tube.

Kolas

EDIT: My apologies, this tube DOES need to be air cooled as well. Thank you for bringing this to my attention.

The biggest issue with the armstrong oscillator at the moment apears to be my inability to control the voltage that goes to the grid. Since this tube is so "power hungry", raising the grid V 100V too high would cause severe power draw issues, manefesting it's self in B+ filter cap being dumped.

kolas

Steve Conner

Thu Jun 15 2006, 10:01AM

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

Controlling the grid bias in an armstrong oscillator is easy. You just get rid of the grid leak resistor and substitute a negative DC power supply in there. The only problem is that the power supply gets power fed back into it, rather than delivering power, so you have to design it appropriately.

Kolas

Thu Jun 15 2006, 09:38PM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

no no, not just the bias, the power curve is such that i cant raise the grid voltage above -300V otherewise the tube will conduct too much current and discharge my filter capacitor, which is too small anyway. On that note, anyone have a 15kJ capacitor bank at around 10kV?:P

Marko

Thu Jun 29 2006, 12:42AM

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

anyone have a 15kJ capacitor bank at around 10kV?:P

huh, isn't just a graetz or even halfwave rectification enough?

Arcstarter

Sat May 31 2008, 12:19AM

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

I know that this is horribly outdated, but did you ever do anything with this?

Patriot

Sat May 31 2008, 05:03PM

Registered Member #1507 Joined: Tue May 27 2008, 04:05PM
Location: el paso, texas
Posts: 39

Yeah, whatever happened to this project????

Marko

Sat May 31 2008, 05:11PM

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

Well, for what I know, kolas is limited by lack of several things, such as general budget, power supply and filament transformer, Proper insulated water cooling system, and enough insanity.

Indeed, unless he can get full 100kW+ feed from the power company (maybe time to directly connect to utility grid?) I myself don't see this worth of effort over simply getting a smaller tube.

Marko

Dr. H.

Sat May 31 2008, 07:06PM

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

Yes - I agree with Marko - if your power is limited to 15kW - then just use smaller tube, apropriate for such power levels - it will make your life much easier

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