Shunt Reg Using a 13E1 as Shunt Element

Cressy Snr · Post by **Cressy Snr** » Thu Dec 22, 2011 8:34 pm

Right

For a Winter project I'm looking at experimenting with shunt regulators.

I would like to try a shunt reg for the HT to my 6B4G monoblocks and am thinking of using a triode-strapped 13E1 as the shunt element.
The voltages it likes to work at are exactly what I want out of a supply ie around 360V regulated.

Shunting twice the current of the output stage at 90mA is a walk in the park
for this tube as it has a 90W dissipation capability, plus it looks gorgeous, as
all who saw my power amp lit up will testify.

Trouble is I am clueless at the moment about how to design one to fulfil these requirements ie 360V out at 45mA.
Yep...I know I can stack two 0A2s and an 0B2 to get the rough voltage out
but after that I'm stuck.

I've had a look at Steve Bench's site so far but if anyone can point me to some other articles I'd be grateful, Most shunt regs I've seen via google
are only for phono stages or preamps. There does not seem to be a lot of stuff about power stages with shunt regulation applied.

Steve

IslandPink · Post by **IslandPink** » Thu Dec 22, 2011 9:05 pm

Good luck and tell us how to do it Steve. I have a couple of 572B's waiting

Andrew · Post by **Andrew** » Thu Dec 22, 2011 9:12 pm

Hi Steve,

I shunted my 300B using the IXCY parts, the theory is the same for valves as MOSFETS.

http://www.tubecad.com/2007/01/blog0095.htm

http://www.tubecad.com/2007/06/blog0112.htm

http://www.tubecad.com/2007/06/blog0109.htm

there's more too on Broskie's site.

Andrew

Andrew · Post by **Andrew** » Thu Dec 22, 2011 9:20 pm

Here's what I was after....

Feedforward & feedback shunt reg using a depletion mode mosfet, Swap mosfet for your valve, the size of load R (614 and 309 in this case) is approx 1/gm, if memory serves.

Andrew

Cressy Snr · Post by **Cressy Snr** » Thu Dec 22, 2011 9:33 pm

Cheers Andrew

That's plenty of reading

Andrew · Post by **Andrew** » Fri Dec 23, 2011 8:16 am

Oh one more thing, JB missed this, important safety addition!

You need to add a zener diode across the cathode resistor to prevent the cathode voltage rising too high and the device conducting too much at start up. As it starts up the grid will be high too and you can end up in a zero bias failure mode as the shunt starts to conduct too much. I have a sim of this process somewhere, I also saw how, when I powered the shunt off a bench supply, the current limiter kicked in and the milliamp meter went off the scale as it started up.

All in all, in took me a while to figure out why I blew up at least one pair of shunts. And, right now, I don't see any reason why the zener wouldn't be a useful addition to a valve shunt even tho' a valve will take much more abuse before it dies. Having the zener will be much kinder to the valve concerned and its out of the circuit most of the time.

Andrew

Laurence · Post by **Laurence** » Fri Dec 23, 2011 9:04 am

There was once a 211 amp which also used 211 as the shunt reg tube. So if you could find that circuit you could adapt it. I may have read it in Sound Practices. I think the control of the shunt element was with solid state. I can't remember the author or the name of the amp.

Paul Barker · Post by **Paul Barker** » Fri Dec 23, 2011 9:34 am

"Development Notes on a Single Ended 211 Amplifier" Dennis Boyle and John Camille.

They put a 211 at the B+ with the equivalent cathode arrangement as the output valve. They controlled the grid of the shunt valve with solid state. So far I have only found the bare sketch. It was a later article where they detailed the solid state control element.

I have spelled out Steve Benches method using class A2 valves in other threads. Controlling negative bias valves is more complicated. You could do it in the same simple way by placing the VR tube on the cathode of the 13e1 and grounding the grid. But the VR tube to qualify would have to be of sufficient low voltage (AFAIK 75v is lowest) and it would pass the same current as the 13e1.

I will keep digging through the archives in case I turn up the explanation article.

Paul Barker · Post by **Paul Barker** » Fri Dec 23, 2011 9:54 am

Ok it is Sound Practices Summer 1994.

I have just done a quick sweep of the crux of it. Basicaly it is full of concepts I avoid. Loads of error correction by means of feedback using zenners and opamps.

They do point out in their article, (though they didn't blame themselves) that most people didn't like this 211 amp on the Edgar Horns.

Their excuse was that you only need 50mW to 500mW of music power. Now they claim that some nasty artifacts from zenners and solid state used in the recording chain are revealed by their marvelously perfect amplifier, and because of their extreme capability their amp is showing up nasty sounds elsewhere.

I would suggest to take a look at the opamps and zenners on the grid of their shunt valve aswell as those in the recording chain!

I don't think one is allowed to publish this actual article, but I might be able to "lend" it to a friend Steve by electronic means. Be your own judge.

Paul

Cressy Snr · Post by **Cressy Snr** » Fri Dec 23, 2011 10:04 am

Paul you have a PM

Steve

Paul Barker · Post by **Paul Barker** » Fri Dec 23, 2011 10:15 am

you have email.

Paul Barker · Post by **Paul Barker** » Fri Dec 23, 2011 10:21 am

Paul Barker wrote: they claim that some nasty artifacts from zenners and solid state used in the recording chain are revealed by their marvelously perfect amplifier, and because of their extreme capability their amp is showing up nasty sounds elsewhere.

To be fair to them and brutally honest to myself, I too experience this when listening to some music.

As you mostly know I have fully shunt regulated power supply choke input because there are no caps.

Yes I too find that small thin films of cloud are removed after you get your output stage unadulterated by the tone of capacitors and you reduce the ac signal down to another valve vertually completely. (yes I found some tone was coming from capacitors in the power supply after I removed them all else remaining equal.

BUT I imediately all of a sudden found with the extreme extra detail something which made me tired.

This was fixed by shanging the opamp in the cheap ebay dac to a burr brown.

Paul Barker · Post by **Paul Barker** » Fri Dec 23, 2011 1:41 pm

Poor old Steve is probably wading through that article now which is not exactly user friendly. But it was seminal for 1994.

Myself I would be thinking of a simpler solution.

Cressy Snr · Post by **Cressy Snr** » Fri Dec 23, 2011 2:36 pm

Paul Barker wrote:Poor old Steve is probably wading through that article now which is not exactly user friendly. But it was seminal for 1994.

Myself I would be thinking of a simpler solution.

Jeez I managed to get through it but I'm afraid I almost lost the will to live

It's not exactly encouraging is it?

And you're right Paul
I'm thinking of a simpler solution.

I'll post my ideas a bit later on so you can point and laugh

Steve

Post by **Nick** » Fri Dec 23, 2011 2:38 pm

The 45 stage of my old 211 amp used a 13E1 as a shunt. It was based on the SB site and used (I think) a ecc83 as a LTP error amp.

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Shunt Reg Using a 13E1 as Shunt Element

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