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Tonskulus

Thu Mar 26 2009, 12:19PM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

Steve McConner wrote ...

I think what Harry is trying to get at, is that the plate and grid meters are useful to check that the circuit is working properly, and the plate and grid aren't being over-dissipated, no matter whether it's a Hartley, Colpitts, Armstrong or whatever.

I think it's simply that if the manufacturer decides to make the grid drive non-adjustable by the end user, then there is no need to have a meter for it, since the user can't do anything about the meter reading. But as the designer, I'd want to know.

Yes, this is true and thats what i was trying to say. Grid meter is necessary when tuning that circuit but when it is tuned, its ok to leave it out.

Tube should arrive tomorrow so lets see how it works. And yes, i will use grid ammeter at first.

Tonskulus

Fri Apr 17 2009, 09:35AM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

New video available:
http://www.youtube.com/watch?v=ROoN5QFQSqM

Proud Mary

Fri Apr 17 2009, 11:26AM

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

Well done, Tonskulus! A great demonstration!

Watching your demo, I realised why my opinion has so often differed to others on the forum about high power RF design - I often tend to think in terms of a circuit which must be made to work continuously 24/7/365 where everything must be generously under-rated to allow for every kind of hazard when there is no one in attendance, like a Decca or Loran slave transmitter on an island where it has to look after itself for thirty days at a time!! But to operate in short burst as you do is a different matter, as I see.... thank you for the demonstration....

Steve Conner

Fri Apr 17 2009, 04:43PM

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

Yes, around here, high power RF design is done by the method of "Crank it up until it explodes, then back off a quarter turn"

Tonskulus

Sat Jan 09 2010, 09:54PM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

Some news here. I made improvements again for my vacuum tube induction heater. We also acquired EMA induction heater workstation, its just a metal box that contains tank capacitors (two 5nF dralorics in parallel) and 22:1 matching transformer (air core, 22turn primary and 1 turn secondary). First I connected it to my smaller tube oscillator and results were impressive. 500kHz at very high current (hundreds of amperes) gives lots of fun!

Video:
http://www.youtube.com/watch?v=qFq4CujEg_0

Steve Conner

Sun Jan 10 2010, 04:02PM

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

Nice work as usual Tonskulus :) Can you explain how you connected up your tube oscillator to the EMA box?

Tonskulus

Sun Jan 10 2010, 04:44PM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

I tested two different feedback methods that can be used with remote station/matching transformer. If transmission line is very short between generator and RF transformer, both methods are ok.

If remotestation is located further away from the generator, its better that tank capacitors are installed inside of remotestation to minimize transmission line power losses. Thus, we need special feedback transformer. High inductance primary is connected between plate and gnd.

However, if output transformer is in same enclosure as generator itself or transmission line is short enough, feedback signal can be taken from small, few turn primary coil connected in series with tank coil and tank capacitor. This method takes less space.

Schematics here:

I will make special output transformer for my dual 4-250A generator, that EMA one is just too much for it. Plates will go bright yellow if larger workpiece is inserted to work coil. It just sucks too much power from those "tiny" tetrodes, too much work coil current there. So my plan is 40:1 ratio transformer, should be good match for those tetrodes.

btw, that EMA remotestation is from 7.5kW generator, and we have the whole system. We also got RADYNE 12kW / 450kHz tube type induction heater so now we have at least enough spare parts available.. :)

Tonskulus

Sun Jan 17 2010, 08:07PM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

New video (again)..
Water cooling system added now.

http://www.youtube.com/watch?v=tiD1ZunTRH4

Redstone

Tue Oct 11 2011, 01:55AM

Registered Member #2578 Joined: Sun Dec 27 2009, 09:21PM
Location: USA Utah
Posts: 31

I just want to state that tonskulus's first schematic looks very much like a hartley oscilator, if the 2nf capacitor were instead of being connected to commmons, were to go to the gid instead.

I have already tryed this variation and it works but I am not comfortable calling it a hartley yet.

Tetris

Tue Oct 11 2011, 02:23AM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

I still don't understand properly what an oscillator IS... I know its switching back and forth SOMETHING multiple times a second... but I do not understand its applications... maybe wait a few more months and they will teach us in electronics class? They just asked us to throw together about 3 oscillators and did not tell us how it works (though I already knew, wtf is its application??? I can't learn just from a few blinken LEDs, I need some explanational text, speech or video. XD so someone please explain to me what an oscillators function is because mr. scime will not tell us and the only girl in that period. :P he did give us a bipolar LED which I found quite an oxymoron...

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