The Official Dual Rail Thread

[mooreamps]

yeah, that's right. I was trying to see if gary could be led through realizing that he didn't draw the schemo correctly. Dang. Now the surprise is spoiled! :d

schematic is drawn correctly...

yep, you'd get a pot full more than 600v. The variable losses in the tube rectifier make it soggier than that, but close.

I was going to get him to lambast me about how it actually worked and then lead him into that one. Near as i can tell, he probably gets about 600 and 300, and so he made the intuitive leap to the secondary ac being the same as the output dc. Which means he either doesn't know how a rectifier/capacitive filter works or can't articulate it if he does know.

b8llsh2t... 775 volts unloaded ; right at 600 volts when i bring up the power tubes. You wantna f8ck!ng bet me ; yfmo.........

[imaradiostar]

As I used to say on the vortex- in before the lock...or in before the ban. This isn't acceptable conversation any longer.

[Gregg]

I once watched and took notes while a fellow derived Maxwell's Equations on a black board (this was before whiteboards) in 50 minutes, start to finish.

If you're talking about Maxwell's original 20 quaternion equations with 20 variables 50 min is a very good time

[R.G.]

If you're talking about Maxwell's original 20 quaternion equations with 20 variables 50 min is a very good time

Well, I do remember that for those of us who used ball point pens, there were thin curls of smoke from the tips of the pens.

[Steve Conner]

What exactly did he derive them from?

The whole point of Maxwell's equations is that he discovered them. Or at least, he took the existing equations for electric and magnetic fields: Gauss's law, Ampere's law and so on, and added one new term, displacement current. There was no mathematical way to derive that new term, he must just have decided to try it for fun. He probably just liked the idea, that if he assumed the existence of displacement current, the whole mess could be put into the form of a wave equation, and he could have electromagnetic waves.

In Maxwell's day, there was no equipment capable of measuring displacement current, but now we deal with it every day. (It's what makes your guitar hum louder when you take your hands off the strings.)

[Gregg]

The original Maxwell equations are describing very complex phenomena which are still not well known to modern physics (or according to some deliberately left out). Because the equations were too complex they were reduced later mainly by Heaviside to the well known few equations. Even Lorentz had to do some "reducing" to get rid of some phenomena initially included by Maxwell in his original equations.

[Steve Conner]

Oh no, not more free energy conspiracy theories. References from peer-reviewed journals or it didn't happen.

[Gregg]

Oh no, not more free energy conspiracy theories.

I don't know about that or about complex mathematics. Just mentioning other opinions on the subject. But that's irrelevant to the thread anyway.

[tedmich]

Larry Niven (yes related to David) had a Maxwell's Demon in one of his short stories; he was very small and made sure the faster moving air molecules left the cave, kept the slower moving ones, kept it cool.

[imaradiostar]

So, back on topic. I bought a bag of SPP04N80C3 before they were listed as obsolete- maybe because they were cheap. They're a 4 amp 800 volt part. I have a few transformers that result in plate voltages in the 500 to 550 volt range- a little too high for the screens of some of the tubes I intend to use. I'm going to make a super simple zener + mosfet screen voltage regulator and see how it goes! I figure I should be able to easily get 75 or so watts from 6L6's or EL34's depending on output impedance.

Jamie

[Steve A.]

Resurrecting an old thread from 2010

Well since my OT Plate Load thread kinda morphed into that, I figured I'd start a separate thread dedicated to dual rail technology...

Can someone post a link to the OT Plate Load thread?

Thanks!

Steve Ahola

[defaced]

I think this is it. http://music-electronics-forum.com/t18454/

[xjbear]

There were a few dual rail Univox's from '69-'70 I believe. I own a 1001 and rebuilt it and it sounds freaking amazing. anyway heres a schematic that's pretty close, this ones for a 1011. It works and kicks ass and its still running on the original power tubes and pre amp tubes 44 years later.

[JC1]

I think it's best to think of a so-called "dual rail" amp as just an ordinary amp with the following modifications:

Add on an extra, higher voltage supply just for the plates, and increase the OT load impedance.

You could modify any amp in this way, there are no special requirements.

If you doubled the plate supply voltage, and doubled the load impedance, you'd get twice the output power from the same tubes. But with the following caveats:

1) Too much voltage and things (OT, tubes, tube sockets) might arc and break down.

2) You have to bias it colder, because doubling the plate voltage also doubles the idle power dissipation for a given idle current. This will affect the tone.


My experience with dual rails was with my old Ninja Toaster design. I started with a PT that gave 550V DC, and thought this was too high. So I installed a MOSFET-based regulator with two outputs: 475V for the plates and 360 for the screens. I also had a 6.6k OT, and this worked great with EL34s giving exactly 50 watts with a 1k shared screen resistor.

But with 6L6s it would only give 30W. I installed a switch to bump the screen voltage up to 475, and this gave 50 watts with 6L6s. But flipping this switch with EL34s installed, they tried to make nearly 70W with an impressive light show of glowing screens.

It works with every tube I've tried, from 6V6s to KT88s, on one setting or the other. Well apart from those CV4060s I bought on Ebay, which were a complete disaster. Those would be great for dual-rail amps, because they need a REALLY low screen voltage: even 360 was too high. People sell them as 6550 replacements, but that's misleading, they're more like a 6146B without a top cap.

CV4060 / S11E12 / VX6114

I'm currently using the Sovtek "Tung-Sol 6550s" on the 360V setting, and get about 60W. Oddly I get the same power whether I use an 8 ohm or a 16 ohm load, but that suits me fine because the OT only has one tap.

Lately I turned the regulated voltage down to about 400V, because since I started using the larger tubes, the regulator dropped out and sagged that low under heavy load anyway. That would decrease the screen voltage to about 310, 320.

I've had it for 10 years and I've never seen it blow a power tube yet. I guess one day it will happen and, as per Murphy's law, take the MOSFETs with it.

People say that an amp with a regulated power supply must sound bad, but I've always enjoyed playing it.

Steve, I like your idea, could you furnish a schematic of this? I'd like to look it over for an idea in one of my amps. I'm the one running KT90's in a modified Marshall, 1983 JCM800 4210 50w (was 50, now 70'ish) & I changed the PT from a 390v plate voltages to now 500 - 520v on the plates. I'm thinking of converting back to EL34's or a nice pair of KT77's brown base ones I have still lying around and would like to either make a switch or just lower the screen voltage to a more safer level, say 450-460v, but leave the plate voltage alone. I've considered the Zeners in series with the screen resistors or maybe your seperate Mosfet regulators.

I get about 570v before load & 458v loading right at on set of clipping or 72w. Before it was 36w with KT77's and the old 390v PT.

Thanks. JC

[Steve Conner]

Stabilised power supply

There are simpler ways of doing it of course