Gas regulator tubes (VR tubes)

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Max N
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#1 Gas regulator tubes (VR tubes)

Post by Max N »

I've seen a couple of circuits recently where the HT supply uses a solid state CCS feeding a gas VR tube(s)

There's the one that Mark linked to in Richard's thread
http://www.nutshellhifi.com/GarysAurora.gif

And this one
http://www.nutshellhifi.com/preamp.gif

In both cases, it seems to me that at start-up, or if the amp is powered up without tubes in, or if for any other reason the load current falls to zero, then the current through the VR tube will exceed the rated maximum current. Am I missing something? Is it actually safe to operate VR tubes like this?

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Max
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Nick
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#2

Post by Nick »

Well, its unlikely that anyone will die. I try (like in the phono you borrowed) to keep the CCS current to less that the max current of the VR tube. Those circuits may not, which as you say is a bit naughty. But a lot of circuits out there only need one failure to go badly wrong.
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Paul Barker
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#3

Post by Paul Barker »

Also don't forget Max VR tubes are valves not solid state, solid state devices 1% over absolute max and you have a fuse.

Valves shrug off abuse way over their max ratings for a prolonged period.

in the scenario where a vr tube is shunting current it is similar position to a capacitor. in either case when something goes wrong elsewhere to cause voltage increase above rating of capacitor or current pull beyond ratings of VR tube it is a hang tough situation until someone notices something is wrong and cuts the power.

Either would hang on for a 1/3rd over their rating and work later as normal.
Go over that it would probably survive but future performance handicapped. Go over 1/2 and probably lights out. Brown smelly stuff comes out of end of capacitor, Vr tube glows very bright, but doesn't die absolutely like the capacitor, though it is quite likely crippled. Nicads which are pushed over their current go off like party poppers and fire strands of something across the room.

conversely silicon devices make no fuss at all, but never work again in any way shape or form without a warning.

Out of the devices I estimate the solid state is safest as it fuses. the VR tube is pretty safe i have made a few go to destruction they don't set fire or anything, not even get hot, they go brighter and a different to normal colour, if you persist they go out all together never to work again. Valves get reduced transconductance to none in the event of total failure. Which tends to be a fairly safe end to the situation. capacitors batteries and resistors are the danger. they give off toxic substances in their death throws and could generate enough heat to cause a fire.
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Nick
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#4

Post by Nick »

conversely silicon devices make no fuss at all, but never work again in any way shape or form without a warning.
I had a mosfet in a power conditioner/UPS go bang with a very loud bang and bits of plastic shooting across the room. But mostly they go gentle into the good night.
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#5

Post by Andrew »

What you let the magic smoke out? They don't work when you let the magic smoke out......
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Nick
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#6

Post by Nick »

The magic smoke insisted on coming out, and it wanted to show the world the little bit of silicon inside.
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Max N
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#7

Post by Max N »

OK, thanks guys - I will stop worrying about poor abused VR tubes :D
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Paul Barker
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#8

Post by Paul Barker »

ah well the thing is you don't operate them outside their limits. But you don't have to be critical about what might happen to them if failure in another part of the circuit takes them over. They would probably survive for long enough while someone realising the music has stopped gets out of his chair and turns off.

When in puting together direct coupled amps of the scary type, if there is a failure due to over voltages and currents it tends to be the triodes which go before the Vr tubes. though i have killed both while tuning in a design. what I have has not been arrived at without empirical research. I have learned a lot empirically and very little theoretically.
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Dave the bass
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#9

Post by Dave the bass »

Nick wrote: I had a mosfet in a power conditioner/UPS go bang with a very loud bang and bits of plastic shooting across the room.
Yep, we repair a PSU called a Bio Rad PowerPac 300 that does that on occasions. We get a report of "no longer working, seems to be something loose inside...". Open up casework and there's often a MOSFET nekkid inside showing its innermost workings, it's clothes scattered in bits across the PCB.

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#10

Post by ed »

Nick wrote: I had a mosfet in a power conditioner/UPS go bang with a very loud bang and bits of plastic shooting across the room. But mostly they go gentle into the good night.
should only work with FETs that have attitude, but it is good to choose those that are aware of Dylan Thomas.......... dismiss the namby pambys!
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#11

Post by IslandPink »

In the cases shown, you won't be getting any music, and you'd pretty quickly ask yourself - why did I take the valve out of its socket ?
:!:

I never had a case where this caused a problem , it's just an unlikely occurance.
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#12

Post by Mike H »

Dave the bass wrote:Yep, we repair a PSU called a Bio Rad PowerPac 300 that does that on occasions. We get a report of "no longer working, seems to be something loose inside...". Open up casework and there's often a MOSFET nekkid inside showing its innermost workings, it's clothes scattered in bits across the PCB.

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lol .. :lol:
 
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pre65
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#13

Post by pre65 »

A valve based (pun :wink:) turkey fryer ?:shock: :lol:
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Mike H
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#14

Post by Mike H »

I got a "this topic or post does not exist" for this one Image
 
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