Tube Voltage Regulator Flicker...

sonata149 · 1st March 2007, 08:06 PM

I built an SE amplifier using 807s with the screen grid 250 volts fed from two valve regulators. On crescendo passages, the VRs' glow flickers - brightens and dims and even blocks out. At first I thought it was the bass but it also happens with rich female vocals (Mina - this evening).

Has any member had a similar experience with VRs? Any info and guidance would be greatly appreciated. Thanks - Joe A

EC8010 · 1st March 2007, 08:17 PM

You need more quiescent current through your VR valve.

kevinkr · 1st March 2007, 08:37 PM

Had no idea that Mina was still around. My sister's preferred artist for a while..

Reduce the value of the dropping resistor feeding the regulator tubes, depending on type they can handle up to about 30mA or so quiescent. A slight amount of flicker is acceptable at high levels, but they should never extinguish.

sonata149 · 1st March 2007, 08:38 PM

Thanks EC8010. As I'm not very technical, does that mean I should lower the value of the dropper resistor?

EC8010 · 1st March 2007, 09:08 PM

Yes, as kevinkr says. If you can post a diagram, we can even tell you what value to reduce the resistor to.

Miles Prower · 1st March 2007, 09:27 PM

Quote:

Originally posted by sonata149
I built an SE amplifier using 807s with the screen grid 250 volts fed from two valve regulators. On crescendo passages, the VRs' glow flickers - brightens and dims and even blocks out. At first I thought it was the bass but it also happens with rich female vocals (Mina - this evening).

I would not rule out the possibility that your regulator isn't completely stable. You might have a damped oscillation in there. You'll need to o'scope to see if this is happening.

Johan Potgieter · 2nd March 2007, 12:55 AM

I agree with Miles.

In days of yore we had several occasions of less than perfect tube regulators. Also, take into account that with beam tubes the g2 current can vary appreciably between low-max. output. You do not mention whether the VR tubes are used as primary regulators or whether they form part of a higher current tube regulator. Whatever topology, the problem is the same. Make sure the regulator can cope.

jlsem · 2nd March 2007, 04:37 AM

Quote:

You need more quiescent current through your VR valve.

I agree with EC8010. In a Class A 807 amp the screen grid (@250V) will probably not draw the 5ma minimum current requirement of most gas regulator tubes.

John

sonata149 · 2nd March 2007, 02:28 PM

Hi Folks,

Thanks a lot for your feedback. Although it's getting a bit confusing for me (with damped oscillations), I'm starting to think seriously about it. I have dropped the resistance by about 500 ohms and I'm still getting the same results.

I'll post a diagram of that section later on as I'll be out. But I wanted to say thanks to you all for your help.

kevinkr · 2nd March 2007, 02:45 PM

Depending on the value of that resistor you may need to drop to something like half its current value. As a minimum you would probably need >25mA flowing through these vr tubes if they are supplying the screens of both output tubes.

Got your email, am writing a long winded reply..

1st March 2007, 08:06 PM	#1
sonata149 diyAudio Member Join Date: Sep 2006 Location: Malta, Europe	Tube Voltage Regulator Flicker... I built an SE amplifier using 807s with the screen grid 250 volts fed from two valve regulators. On crescendo passages, the VRs' glow flickers - brightens and dims and even blocks out. At first I thought it was the bass but it also happens with rich female vocals (Mina - this evening). Has any member had a similar experience with VRs? Any info and guidance would be greatly appreciated. Thanks - Joe A

1st March 2007, 08:17 PM	#2
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	You need more quiescent current through your VR valve. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

1st March 2007, 08:37 PM	#3
kevinkr Contributing diyAudio Member Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 4	Had no idea that Mina was still around. My sister's preferred artist for a while.. Reduce the value of the dropping resistor feeding the regulator tubes, depending on type they can handle up to about 30mA or so quiescent. A slight amount of flicker is acceptable at high levels, but they should never extinguish. __________________ www.kta-hifi.net

1st March 2007, 09:08 PM	#5
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	Yes, as kevinkr says. If you can post a diagram, we can even tell you what value to reduce the resistor to. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

2nd March 2007, 02:45 PM	#10
kevinkr Contributing diyAudio Member Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 4	Depending on the value of that resistor you may need to drop to something like half its current value. As a minimum you would probably need >25mA flowing through these vr tubes if they are supplying the screens of both output tubes. Got your email, am writing a long winded reply.. __________________ www.kta-hifi.net


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1st March 2007, 08:38 PM	#4
sonata149 diyAudio Member Join Date: Sep 2006 Location: Malta, Europe	Thanks EC8010. As I'm not very technical, does that mean I should lower the value of the dropper resistor?

2nd March 2007, 12:55 AM	#7
Johan Potgieter diyAudio Member Join Date: May 2005 Location: Pretoria, South Africa	I agree with Miles. In days of yore we had several occasions of less than perfect tube regulators. Also, take into account that with beam tubes the g2 current can vary appreciably between low-max. output. You do not mention whether the VR tubes are used as primary regulators or whether they form part of a higher current tube regulator. Whatever topology, the problem is the same. Make sure the regulator can cope.

2nd March 2007, 02:28 PM	#9
sonata149 diyAudio Member Join Date: Sep 2006 Location: Malta, Europe	Hi Folks, Thanks a lot for your feedback. Although it's getting a bit confusing for me (with damped oscillations), I'm starting to think seriously about it. I have dropped the resistance by about 500 ohms and I'm still getting the same results. I'll post a diagram of that section later on as I'll be out. But I wanted to say thanks to you all for your help.

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