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Old 7th November 2012, 10:07 PM   #31
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Information on VR tubes here



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Old 8th November 2012, 08:28 AM   #32
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Originally Posted by DF96 View Post
Explain what? The voltage drop across the upper element during normal operation has nothing to do with striking voltage. Striking voltage is the applied voltage at which the regulator begins to conduct, thus reducing the applied voltage. This tells you nothing about the voltage on the other end of the resistor/CCS.
I think it's fair to ask for an explanation of how to use VR tubes with a CCS - there's nothing in the data sheets or application notes about this since they were written before such devices were used. We know the voltage on the load which is 150v in the case of a 0D3, and we have the "headroom" needed for a VR to strike with a resistor, which is 35v above 150v.

My question is what headroom do you need with a CCS? In previous posts it's stated "apply any voltage to the CCS and it will do it's job", but is there a minimum voltage that needs to be supplied to the CCS above the 150v? And does this headroom change for one or two devices?
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Old 8th November 2012, 09:51 AM   #33
DF96 is offline DF96  England
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Any CCS will have a minimum voltage for normal operation, but remember that a non-conductive VR will take very little current (almost zero) so the CCS will probably have very little voltage drop across it at first. However, once the VR strikes the CCS must be able to supply the required current.

Your question is actually about CCS, not VRs!

If the CCS drops too much voltage for VR striking but is OK when running normally then you can add a resistor and diode to fix this situation, provided that the supply rail is above the strking voltage. The CCS feeds the load, whatever that is. A high value resistor (few hundred k ish) feed the VR and ensures striking. A rectifier diode connects the two junctions together, arranged so that it is reverse biased before striking but forward biased once the VR pulls its side down. You can see a similar arrangement here, although for different reasons.
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Old 19th November 2012, 01:54 AM   #34
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Hey All,

I want to use a VR150 in My RH84 to regulate screen voltage for 6P15P's. I found this formula; Source voltage - regulated voltage/ mean current + load current = series resistance. So for the RH it would be 300 - 150 / 22.5ma + 9ma = 4.76ohms? Does that sound right? And you all seem to be saying the tube needs a bypass cap? .1uf @ 300volts? Also, The current window for this tube is between 5 and forty ma. Is the 9ma grid current of the 6P15P's too low for the tube to work properly? Or do I have to add a parallel resistor with the load to get to the mean current of 22.5?
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Old 19th November 2012, 08:24 AM   #35
12E1 is offline 12E1  United Kingdom
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Quote:
Originally Posted by mr2racer View Post
Hey All,

I want to use a VR150 in My RH84 to regulate screen voltage for 6P15P's. I found this formula; Source voltage - regulated voltage/ mean current + load current = series resistance. So for the RH it would be 300 - 150 / 22.5ma + 9ma = 4.76ohms? Does that sound right? And you all seem to be saying the tube needs a bypass cap? .1uf @ 300volts? Also, The current window for this tube is between 5 and forty ma. Is the 9ma grid current of the 6P15P's too low for the tube to work properly? Or do I have to add a parallel resistor with the load to get to the mean current of 22.5?
You have an error in the maths...

300V - 150V = 150V

22.5mA + 9mA = 31.5mA

150 / 31.5mA = 4761 ohms (use 4.7k ohms, 5 watt minimum - 10 watts would be good)

(clue - you are using milli-Amps, not Amps).

But why choose 22.5mA? You don't need to reach the average current level. Wouldn't 10mA though the regulator give the same result, save power and wasted heat and also give longer life, ?

(300V - 150V) / (10ma + 9ma) = 7984ohms (so use 8.2k ohms, 3 watt minimum - 5 watts would be good)
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Old 19th November 2012, 10:26 AM   #36
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Thanks 12E1,
My degrees are in English and Geography. I'm truly awful at algebra. The website I found said the draw should be in the middle of the tube's range. If it will work at 10ma all the better! Thanks again, Math challenged
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Old 19th November 2012, 12:59 PM   #37
12E1 is offline 12E1  United Kingdom
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Some VR150 data specifies a range of 5 to 30mA, so I would be very happy running it at the 10mA level. You should be able to go a bit lower still if needed. then you can go with a 10K 3watt resistor - would probably be easier to find.

Last edited by 12E1; 19th November 2012 at 01:02 PM.
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Old 19th November 2012, 09:20 PM   #38
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I found an 8k, 5 watt, 5% wire wound at Digikey for $1.55. Can't get much closer than that.
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Old 20th November 2012, 01:04 AM   #39
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Don't forget, the screen current isn't constant... you need to allow enough for peak screen draw - and the VR tube draws the extra current in the meantime. If the VR tube goes out on audio peaks, you need more current.
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Old 6th December 2012, 03:30 AM   #40
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Hey Guys,
I used the 8k series resistor. but I could only get 2ma for each screen. And the result is only 15ma draw on the 6P15P. I changed to a 6.8k series resistor with no change. Still only 2ma to each screen grid. What am I doing wrong? When I had just a 10k resistor between B+ and the grids the tube drew 28ma so I'm pretty sure the problem is in the regulator circuit.
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