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Old 15th October 2008, 05:12 PM   #21
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Quote:
Originally posted by bequerel
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?

Yes, this is why it is VR Safety for Dummies. The CCS will, in essence, figure out how much voltage to drop for you. Just be sure the CCS has a proper heatsink, and you can feed it anything you like.
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Old 15th October 2008, 05:27 PM   #22
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As I said, use a VR tube with a source follower, such way you keep current through it relatively stable, also you can implement a RC filter from it to gate, so no shunting capacitor is needed. I use such approach in several models of my amplifiers, it works fine, and tubes are glowing many years without need to replace them.
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Old 16th October 2008, 06:40 AM   #23
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Quote:
Originally posted by dsavitsk



Yes, this is why it is VR Safety for Dummies. The CCS will, in essence, figure out how much voltage to drop for you. Just be sure the CCS has a proper heatsink, and you can feed it anything you like.

Cool, thanks!
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Old 1st November 2012, 03:21 AM   #24
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Hey Guys,
I want to use a VR150 to regulate 2nd screen grid on a 6P15P and 6GK5 plate voltage in an RH84 SE amp. I found the formula to derive the load limiting resistor. But I still have a couple questions. First the data sheet says input voltage minimum is 180 volts but doesn't spec a maximum. Can the source voltage be at B+? In this case 300 volts? Second, the mean amperage is 22.5ma. Two 6P15P grids and two 6GK5 plates total 32ma. Will this allow enough range that it won't overamperage the tube and cause arcing? And lastly the bypass cap mentioned earlier is to shunt noise? And should be an electrolytic?
Thanks, Kevin
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Old 1st November 2012, 03:23 AM   #25
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PS I was thinking of using the RH84 as the front end for a large SE amp. A pair of KT120's in parallel. Any reason this wouldn't work?
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Old 1st November 2012, 04:39 AM   #26
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Kevin, I have a little test rig here that I use to quickly check VR tubes. Off load voltage is 330v and doesn't give any problems with any good VR tubes (it finds the ones that have had their gas leak out though).
If you are concerned about the current carrying capability, get the VR150/30 version, it is rated at 30mA continuous.

Gary
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Old 1st November 2012, 04:59 AM   #27
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Quote:
Originally Posted by Andrewbee View Post
Hi all,

Quick ?,

I am rebuilding my RH84 (EL84 Pentode SE) and am considering regulating G2.
I have never used Gas tubes before, only zeners but have a VR150. So, I am thinking about the VR150 and was wondering if there would be a problem using it with SS rectification for the B+.
Makes no difference. If you've used Zeners, VR tubes are no different. Just make certain you don't connect a capacitor in parallel. Being that it operates by means of a glow discharge, that means a negative resistance characteristic the Zener doesn't have, and negative resistance means possible oscillation. Also, the noise that Zeners make is more objectionable than that of VR tubes.

Quote:
I did read somewhere that they do not like being turned on and off and on again quickly.
They don't. The spec sheets usually tell you to make sure they operate for ~20 minutes. Otherwise, you could compromise the accuracy of the regulation. I use 'em for voltage references:

Le Renard Screen Regulator

Works like its SS counterpart, and have not required any adjustments since this began service five years ago. Future iterations won't require a variable resistor, since once set, it hasn't been touched at all. In this case, the VR tube isn't under any sort of load, doesn't need to pull any big currents, and a simple RC LPF is really all you need for noise protection.

The pentode half of that dual requires special attention to layout details and stoppers since it's a high gain pent. Since the screen voltage required is just 150Vdc, the Vhk ratings aren't stressed, and so don't require a separate heater xfmr with a voltage lift to keep from exceeding a Vhk limit.
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Old 2nd November 2012, 12:35 AM   #28
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This might help: The VR Tube
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Old 7th November 2012, 08:08 PM   #29
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I tried feeding a VR150 with a DN2540 and then with an IXYS 10M45. Both worked OK. For 58mA (36mA load plus 22v for the VR150) with a dropper resistor the B+ before the resistor is 200v. With the IXYS it's 180v. With the Supertex it's 172v. In all cases the VR150 lights up.

The stated strike voltage is 185v with a resistor. In both cases, with the active devices, the strike voltage is less than that.

Can anyone explain this?
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Old 7th November 2012, 09:01 PM   #30
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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.
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