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Old 13th October 2008, 08:54 PM   #11
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Thanks guys,

Lots of help. The only issue it appears I may face is the screen current may be insufficient with the EL84's. I guess I will try and see.

Thanks for the link Kevinkr.
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Old 13th October 2008, 09:23 PM   #12
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Quote:
Originally posted by Andrewbee


Lots of help. The only issue it appears I may face is the screen current may be insufficient with the EL84's. I guess I will try and see.

Use source follower, something like IRF-730
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Old 13th October 2008, 09:39 PM   #13
kevinkr is offline kevinkr  United States
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I think you'll probably be ok with a single VR tube or series string to get the voltage you need. The EL84 generally does not require more than 10mA of screen current per tube, and if you use a tube rectifier to delay the B+ there will be a window within which the VR tube can live. The issue is just to make sure that you are ready to draw screen current when the VR tube starts to conduct.

You can also just use a B+ delay relay with a simple timer circuit.

Alternately you can use 0A2/0B2 pairs for each channel.. More glow = more fun..
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Old 14th October 2008, 11:02 PM   #14
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if for some reason, you wanted to use a bigger cap than .022 accross a VR, could you not put a diode between the VR and the cap, to prevent it oscillating...?
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Old 15th October 2008, 01:02 AM   #15
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All of the datasheets I've seen, as well as my own experience, suggests that 0.1u is fine. Why all the sudden concern?
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Old 15th October 2008, 03:14 AM   #16
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by Alastair E
if for some reason, you wanted to use a bigger cap than .022 accross a VR, could you not put a diode between the VR and the cap, to prevent it oscillating...?

Yeah, but it also prevents the cap from doing its job once the cap is fully charged.. (Cap is essentially disconnected once the diode is no longer forward biased.)
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Old 15th October 2008, 03:18 AM   #17
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by dsavitsk
All of the datasheets I've seen, as well as my own experience, suggests that 0.1u is fine. Why all the sudden concern?
Hi Doug,
I think that was only one of the concerns, and I have had problems at 0.1uF (probably cap tolerance issues) and generally use less..

The other concerns related to not roaching the VR tube(s) during warm up..

I use them all the time too, and have not had any problems recently.. I have seen others put them in arc mode under certain unanticipated operating conditions though which can be rather exciting.. (Like driving the outputs into cut off with already excessive current present in the screen regulator VR tube.)

Them pyrotechnics were somethin' to see..
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Old 15th October 2008, 04:00 AM   #18
rdf is offline rdf  Canada
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Quote:
Originally posted by kevinkr
I have seen others put them in arc mode under certain unanticipated operating conditions though which can be rather exciting..
That's why I like the CCS option: VR Safety for Dummies. The extremely high impedance ratio also drive noise well into the dirt.
On the topic, how does everyone handle series VR tubes? Currently I'm running a single 0.1uF cap across a series pair. It seems to me possible that ~0.05uF across each VR and one across the series string would also work. Individual VRs would see the 0.05uF across it in parallel with the other two 0.05uF caps in series, effectively 0.075uF across each VR but .15uF in the supply. Make sense? Worth it?
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Old 15th October 2008, 03:12 PM   #19
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Quote:
Originally posted by kevinkr



Yeah, but it also prevents the cap from doing its job once the cap is fully charged.. (Cap is essentially disconnected once the diode is no longer forward biased.)


Perhaps I wasnt clear. You have a supply feeding the VR from +B via resistor. The VR is connected to ground. The diode is connected to the VR hot side, and the cap connected to diode and ground. You take regulated volts from across the cap....
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Old 15th October 2008, 03:43 PM   #20
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Guys,
How do you calculate the voltages when using a CCS to feed a VR150 tube?

Let us say that the VR150 needs 200V to work correctly and ignite, and that the CCS needs a voltage drop of minimum 30V to work.
Can I just make sure that my power supply delivers minimum 230V (220V + 30V) to the CCS?
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