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Old 22nd March 2013, 01:24 PM   #2841
stajo is online now stajo  Sweden
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Quote:
Originally Posted by andyjevans View Post
The 75v glow tubes are pretty spectacular! But for Filipe and for myself as well, I prefer a single tube so you avoid the problems of getting two tubes to strike. Mind, the DN2540 does seem to fire up a couple of tubes pretty well. You can wrap a resistor around the top tube.
I think Mogliaa did some measures and got really good results from some russian VRs combined with a CSS but I dont seem to find it now, the article is probably archived somewhere in his excellent site.
http://www.bartola.co.uk/valves/
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Old 22nd March 2013, 01:46 PM   #2842
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Originally Posted by CV6045 View Post
Hi Andy,

Attached is a diagram which may explain it better. Since the Filament is fed with AC...hum can be cured by reversing either the Mains input or the leads feeding the filament. If that does not work then trying something like a 0.22uf from one side of the filament to ground also works. I know I have tried this a number of times
We must be talking about different things - there's a few threads going on. Your diagram is OK for the usual kind of AC (or DC) bias with a bypassed cathode resistor, but it's not filament bias, like Abe and Filipe are using. Maybe I missed the post you were referring to.
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Old 22nd March 2013, 01:46 PM   #2843
Magz is offline Magz  United States
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Quote:
Originally Posted by andyjevans View Post
The 75v glow tubes are pretty spectacular! But for Filipe and for myself as well, I prefer a single tube so you avoid the problems of getting two tubes to strike. Mind, the DN2540 does seem to fire up a couple of tubes pretty well. You can wrap a resistor around the top tube.
I run a CCS-fed VR150 + VR75 on each channel to drop 300V from the supply down to 225V, which is then fed to a second CCS on the plate that drops it down to ~135V or so at 7mA. Sounds excellent.

I don't have any problems with striking them, my trick is to use a choke input B+ supply that depends on the VR tubes to dump enough current to stay in choke input mode. Until they strike the voltage will rise up to that of a cap input supply, ensuring that there is plenty of voltage to strike the tubes. They strike after 1-2 seconds, without fail.

Of course, all the components are rated to easily withstand the max voltage from the "cap input" just in case a VR tube fails.
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Old 22nd March 2013, 02:51 PM   #2844
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@andyjevans
YHPM & email
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Old 22nd March 2013, 02:55 PM   #2845
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Originally Posted by massimo View Post
We shall consider the VAC fluctuation as well, thus the reg should operate from 210 to 240 VAC at least.
Waiting for Rod's final word
What about your work in progress?
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Old 22nd March 2013, 03:00 PM   #2846
massimo is offline massimo  Italy
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Originally Posted by merlin el mago View Post
What about your work in progress?
Still in progress.... No spare time
Two small pcbs missing. As soon as I will etch the new FolCas RIAA boards....
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Old 22nd March 2013, 03:03 PM   #2847
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Still in progress.... No spare time
Two small pcbs missing. As soon as I will etch the new FolCas RIAA boards....
Please post the pics of the boards in the Simplistic NJFET RIAA thread.
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Old 22nd March 2013, 03:39 PM   #2848
massimo is offline massimo  Italy
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When ready.
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Old 22nd March 2013, 03:41 PM   #2849
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OK.
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Old 22nd March 2013, 04:31 PM   #2850
regal is offline regal  United States
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Originally Posted by Magz View Post
I run a CCS-fed VR150 + VR75 on each channel to drop 300V from the supply down to 225V, which is then fed to a second CCS on the plate that drops it down to ~135V or so at 7mA. Sounds excellent.

I don't have any problems with striking them, my trick is to use a choke input B+ supply that depends on the VR tubes to dump enough current to stay in choke input mode. Until they strike the voltage will rise up to that of a cap input supply, ensuring that there is plenty of voltage to strike the tubes. They strike after 1-2 seconds, without fail.

Of course, all the components are rated to easily withstand the max voltage from the "cap input" just in case a VR tube fails.
\I am surprised that the VR tubes don't add hiss?
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