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Old 28th January 2003, 03:46 PM   #1
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Default HV Valve Shunt reg.

I have been looking at how to build a valve shunt reg for high voltage based on my experience with ss shunt regs. There I found that simple disceate designs were easier to optimise than more complex designs - and sounded better.

I have come up with a simple circuit and wonder you would be kind enough to critique it. I've not designed valve regs before so all comments welcome...

Thanks

James
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Old 28th January 2003, 04:22 PM   #2
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Seems to me the VR90 is a waste and could be done instead with a resistor divider from the +105V.
I have no idea what your error amp is, but you'll probably need extra bias current to your VR105.

The plate load resistor on the input side of the diff amp looks superfulous. Come to think of it, the diff won't work at all since the cathode is held constant!

I've never heard of a VR280(?!?) but you can probably get by with less, depending on the Gm of the shunt tube, and perveance of the error amp.

Personally, to regulate 1250V, I might use a more typical pass arrangement (which is also more efficient) and just load on some 0A2s for a floor of say, 900V. (Or zeners, if I had 'em..)

Tim (you'll mostly hear pass regulator from me, since that's what I have more experience in designing )
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Old 28th January 2003, 05:19 PM   #3
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First, I should make it clear that I have not actually built a valve shunt regulator.

I have wondered about valve shunt regulators. The key problem is that the shunt element only needs to see a few volts on its grid, yet needs to be DC coupled to another valve's anode.

Why not earth the cathode of the shunt element, add a subsidiary negative supply, and return the reference and tail of the error amplifier to it? That way, you would avoid large, and variable currents passing through neon references (your VR280). A PL519 (TV line scan valve) would make a very nice shunt element.

Why does your error amplifier have a voltage source under its cathode rather than a current source? What did you have in mind?

Perhaps something like this horrible sketch?
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Old 28th January 2003, 05:31 PM   #4
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Ah! That looks much better.

The idea of a -230V supply seems rather pointless (I want to say stupid, but that word isn't very kind), what with at least 1000V to burn off anyway.

A CCS seems a bit much to bother with in the tail, just use a resistor. We're not going for a perfect phase split, after all.

I'll agree that an EL519 would work fine. A more common tube such as a 6L6 won't, since it has a kV across it. A sweep tube seems perfect, since they were built for HV.

Tim (off to try a higher current tube - 6CD6 instead of 6BG6 - for plasma tweeter/Tesla coil)
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Old 28th January 2003, 06:21 PM   #5
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Default Pointless -230V?

I agree the -230V supply is a pain (and it's going to get worse in a moment), but it allows the cathode of the shunt element to pass directly to ground.

The -230V supply needs a bit of regulation because the potential divider that samples the +1250V and refers it to the 85V reference is sat on the -230V. But all is not lost. The -230V rail passes a constant, small current, so a simple neon reference string and series resistor will suffice.

Just a little thought. Shunt regulators are very rarely proof against open-circuits...

The pentode increases the error amplifier's rejection of power supply noise. If the error amplifier was an ECC83, drawing 1mA per side, then the pentode would only need to sink 2mA of anode current, and an EF91 (dead cheap) would suffice. In fact, any old rubbish would do.
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Old 28th January 2003, 07:08 PM   #6
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Ah yes, good point on the pentode. Come to think of it, you don't need a cathode bias resistor, just use a neon light and voltage divider to hold screen constant. Seems to me Rp depends on current more than relative control grid potential.

Tim
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Old 28th January 2003, 08:18 PM   #7
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Ah, but if you have a cathode bias resistor, its value is multiplied by the mu of the valve, which is an awful lot for a pentode. But you're right, a neon for g2 is a possibility. I suppose it all depends on what you have in stock.

When will the originator of this thread respond? I want to know what he needs the regulator for. Will it stabilise a 2" CRT, or an 845 push-pull amplifier? Details. We want details!
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Old 28th January 2003, 08:39 PM   #8
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Default SHUNT REG.

Hi,

Quote:
When will the originator of this thread respond?
Why do I get a nagging feeling someone I know may find a very good use for this little reggie?
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Old 28th January 2003, 09:10 PM   #9
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Default OK, it's me'eee

Hi,

Thank you James for instigating this thread.
I had nothing constructive to add at it's concepture. In fact I spent a little time wondering how / if it would work.

Yes, a 1250 volt shunt regulator is just what i need for my OnRyoku 845SE amp.
So I'm watching, and listening.
Thank you all for contributions so far.

I'll comment tomorrow when I have some time.

Cheers,
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Old 29th January 2003, 07:44 AM   #10
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Default ..Work is a pain...

Hi Chaps,

Many thanks for all the replies so far - I have a serious problem at work - someone is trying to take us off-air - that I have to sort out before I can think about my replies - sorry. I'll reply later today.

Ciao

James
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