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Old 6th November 2008, 07:05 PM   #11
JoshK is offline JoshK  Canada
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I think it might be Ardon that glows purple. Thyratrons is a general category for gas filled tubes, no?
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Old 6th November 2008, 08:41 PM   #12
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by JoshK
I think it might be Ardon that glows purple. Thyratrons is a general category for gas filled tubes, no?

No Thyratron = gas filled triode, generally used for the same sorts of applications where we today use SCR and triacs. (Power control)
Some small thyratrons were also used in relaxation oscillator circuits and the like.
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Old 6th November 2008, 09:01 PM   #13
coresta is offline coresta  France
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Hi Gianluca , how much current do your 394A last ? I have 20 + left too ciao! Pierre
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Old 6th November 2008, 11:26 PM   #14
Gluca is offline Gluca  Italy
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Ciao

I am using them in my 211 preamp. I believe I am drawing something around 50-60mA. Its a full bridge (thyratrons + solid state diodes) to get 500VDC out of a 300+300VAC transformers.

Thyratrons need many amperes for the filaments. If my memory doesn't fail, 394A filament runs at 3.5A. The bigger 355As and 354As a whopping 15A!

Gianluca
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Old 6th November 2008, 11:28 PM   #15
Gluca is offline Gluca  Italy
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Quote:
Originally posted by kevinkr
have you tried tying grid and plate together?
Hum ... no. Should I?
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Old 7th November 2008, 03:24 AM   #16
Jeb-D. is offline Jeb-D.  United States
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I've seen some Xenon filled rectifiers and thyratrons glow purple.
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Old 7th November 2008, 05:46 AM   #17
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thanks guys for any info...

i have found somewhere this schematic for half wave manually controled rectifier.......
the left transformer is clear - high voltage...
the one in the middle also - heating of the tube....
but the oneon the right is not very clear to me......what's he used for.....
and also - that variable capacitor - what is he used for and how to tune it - to what to tune it.....
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Old 7th November 2008, 06:41 AM   #18
coresta is offline coresta  France
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Hi , this is the heart of the systeml . The variable condenser will change the slope of the sinus voltage fed to the grid and thus change the conducting time of the conducting periode of the gas ... exactly the same as an halogen lamp fed by a variable triac "variator"
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Old 7th November 2008, 02:06 PM   #19
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by coresta
Hi , this is the heart of the systeml . The variable condenser will change the slope of the sinus voltage fed to the grid and thus change the conducting time of the conducting periode of the gas ... exactly the same as an halogen lamp fed by a variable triac "variator"

Coresta is dead right, the left hand transformer provides the grid voltage for firing the tube each half cycle, the phase shift network changes the firing angle so that the half wave output can be "chopped" to vary duty cycle and hence effective power into the load, and the right hand transformer provides the voltage to the load. This is basically a half wave lamp dimmer..

I am not sure whether or not grid and plate should be tied together, I'm just wondering about the dissipation rating of the grid, you are using it in ways for which it was not intended.
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Old 7th November 2008, 02:36 PM   #20
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With the 394A, as Gianluca mentioned using the grid solo drops the PIV from 1250V to around 350V. Tying the grid to the plate, doesn't alter the PIV but it does shift the blue glow up a bit. Sound wise I could not hear a difference between the two connections. In the case of the thyratrons in question, the grid is much larger than the plate so dissipation isn't an issue.

If you need to get more than the 350V from the 394, you need to limit the current to the grid and I found that a 1K resistor from grid to plate allowed me to go upwards of 600V where I ran out of rotation on my variac. I do think I noticed a change in sound when run this way an I'd be interested if Ginluca would try the different configurations and report back.

dave
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