Simplistic Mosfet HV Shunt Regs

[Salas]

Originally Posted by Hearinspace

I have a line stage on the go running VT-25s at about Vp=265VDC / Ip = 30mA.

Right now ICCS is set at ~ 60mA. Vin is about 300VDC and I'll push for as high a Vout as I can so as not to change the operating point of the 10Y more than I need to. I just want to see what sort of influence the shunt regulator will have on the preamp circuit. If it it looks good then next I'll raise the B+ by about 20VDC or so to get your recommended 50V across the CCS. If still good I'll do a newer version on a nice clean board !

35V drop across the reg is still fine. Don't bother raising the reg's Vin in case you like the sound together with your pre. Let us know if it will bring perceivable subjective changes. How did you supply the DHT pre till now? Passive filtering?

[Hearinspace]

Originally Posted by nicoch46

30ma is not too much for 10Y line stage ?

I don't think so. This isn't a power stage but I'm driving a line transformer and it seems to sound best in this set up around 30mA. Vp is much lower than some have used. If I remember it right, Larry Moore recommended running the 10Y at 425Vp-k/35mA ! !

Originally Posted by Salas

35V drop across the reg is still fine. Don't bother raising the reg's Vin in case you like the sound together with your pre. Let us know if it will bring perceivable subjective changes. How did you supply the DHT pre till now? Passive filtering?

I'm running it in a old chassis that has been used a hundred times. The last few tubes have had to put up with power supplies made from the same old parts. This time it's 350VAC>Bridge> LCLC > One LC per channel> OT primary.
(The only thing purpose built for the 10Y's at this point are the heater supply boards from Rod Coleman which I'd highly recommend. I was running LT108- based current regs before this and am really surprised that you can net such an impressive qualitative improvement from there to here.)

I've noticed that if I set up the Simplistic regs and then shut down, when I fire everything up again the regs just sit there with only the CCS Vref voltage difference below the B+ at the output. I have to play with the trimmers again to get them to move. My first thought is that maybe the regulator doesn't like working straight into the reactance of the OT. I'll try a cap across the output to see if that changes it.
Sound ? It's very good but the shift in the tube's op point is too much to be able to make a flat A-B comparison. Fine detail is everywhere - both structural and tonal - yet no sense of dryness or analytic sound. This is all just impressions but it's my guess if I get them running a little more predictably that they'll be excellent.

[regal]

Hearin Space, are you using a separate regulator per channel? If not the ICCS set to 60 mA, is not enough.

[Hearinspace]

Yes, one per.

[Salas]

Originally Posted by Hearinspace

I'll try a cap across the output to see if that changes it.

It better has some ESR. It will surely bring the zero phase cross much lower and maybe like the OT a bit more.

P.S. Go ahead and modify to the newer recommended reg. No point in matching the old. The new one is better in sonics also.

[Hearinspace]

It is as you say master. The left channel decided the low esr cap was just the ticket to freedom and is now gone on holiday. B+ on that side is now a steady and non-negotiable 74.5VDC.

The strangest part of it is that it sounds very nice. I think I've found a new op point for 10Y line stage tubes.

Now to figure out what exactly blew on that board . The heat sink was stone cold . . . . .

[Salas]

The MPSA?

[Hearinspace]

Originally Posted by Salas

The MPSA?

I'll try that one first.

Originally Posted by Salas

It better has some ESR. It will surely bring the zero phase cross much lower and maybe like the OT a bit more.

P.S. Go ahead and modify to the newer recommended reg. No point in matching the old. The new one is better in sonics also.

Which version ? The one with 2SK170 and MJE350?

[Salas]

Yep.

[Hearinspace]

OK. I'll build the new version as soon as I can get the 2SK

It wasn't the mpsa . . .

Any reason you can think of why a two LM336-5 reference diodes (for a 10V ref) in place of the 3 LEDs wouldn't be a good idea? It's what I had on hand and seemed to be a simple choice.

I'll pull the rest of the transistors and see how they are. I'm quickly learning why a roomy layout is a good idea for an experimental board especially when it comes to using small sand parts.