• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

SE SV-811-10 power supply

model vs. breadboard

I modeled my latest design for the B+ power supply in PSUD. Took a screenshot of how it shows the PS will perform at no load (actually a 1mA load). Runs about 870V. Then I breadboarded it and got 865V. Pretty close!
When loaded, I think I will get a bit over 600V B+. The schematic calls for 500, but the SV811 seems like it would be happy with 600. Am I wrong about that?
 

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I was surprised to see this statement in the help section on the transformer/rectifier: "For full wave rectifiers, use the voltage for one side only. For example, if the transformer off load voltage is 350-0-350V (700V end to end), the correct value to enter is 350."
Does that seem right? Isn't that for a half wave rectifier?

Think about it this way:

For a full wave rectifier with the CT grounded, fold it in half and it kinda looks like two half wave circuits in parallel.
 
Progress!

Making some progress on the SV811-10 monoblocks. Pics show one chassis with the layout diagram drawn directly on it. Then I skipped over a lot of tedious cutting, drilling, sanding, priming and painting to show the bookended pair after shooting with a couple coats of two-part urethane.
 

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Power supply coming along

Then the last two are bottom views showing most of the power supply components squeezed in. I was able to get everything into the outside third of the chassis, with a little distance from the driver tube.
 

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Thanks, Audiowize and a question about point-to-point wiring

Audiowize, that is a helpful way to visualize it. Thanks!
Because of the tube layout, there will be a few inches between the 6EM7 and the SV811. Where should the coupling cap go? Close to the driver? To the SV811? In the middle? Or does it matter?
Thanks,
Lewis
 
Tonight's winner in the category of "ridiculously over-engineered"

I want a point to bring all the power supply grounds to, and I want it off the chassis. I didn't have anything suitable, so I made a pair of the little guy in the pic. It's a piece of acrylic stock, center drilled on the lathe, then tapped 10-32 on one end for a button-head machine screw to attach to the chassis, and tapped 10-24 on the other end for a brass stud to collect all the ground leads. Ain't DIY great? Imagine a production shop taking an hour to make a pair of stand-offs!
 

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A question to everyone- some time ago I built a pair of push-pull amps based on the SV572-10. About 80 watts. They sounded great, and looked nice, but I could never get more than a few hundred hours from the tubes. I got a response from Svetlana (can't remember who) that said they were having issues with gassy tubes. Did they ever go back into production? Were the problems resolved?
 
No, the SV572-10 was basically junked because they never lasted that long.

As far as the DC supply for the 811s goes, plan to put a very low value resistor between the + output of the rectifier bridge and your filter cap. I use very efficient, high power schottky diodes and about 0.04R of resistance between the output and cap in my amps to drop the voltage to 6V. This isn't the easiest thing to model, so do some bread boarding to see what you need. Having a little resistance in this position will reduce the stress on your heater winding a bit.
 
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..... got a response from Svetlana (can't remember who) that said they were having issues with gassy tubes. Did they ever go back into production? Were the problems resolved?

The 572 family of Ryazan tubes have the gettering imbedded in the carbon plate. They're made to run with color in the plates, otherwise the gettering doesn't work properly.

I have a triplet of the ceramic base 811A that can still do better than 500 watts at 28 MHz at about twenty years in service. They're getting a little soft, but I've got my money's worth out of them.

Win W5JAG
 
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beyond the power supply

Just a general question:
In the Vacuum Tube Valley schematic (SV811/SV572 SE1), Eric Barbour uses 4 33k resistors in parallel to get to 8.25k.
In the second Glass Audio schematic attached here, he uses 4 12k resistors in parallel/series to get to (I think) 12k.
I'm sure there is a good reason for the multiples, but what is it? Is it just a power handling consideration? But even if that's the point, couldn't I just use a single 5W or 10W of the appropriate value?
Lewis
 

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Some well respected designers have asserted that paralleled resistors sound better... but in this case I’m pretty sure it was a cost saving measure. The design was intended for a budget minded builder. And too, the number is sometimes hard to hit with a single piece.
 
Well, I'm learning that it is difficult to get the voltages you want if the transformer specs are to far off. My 315-0-315 transformer puts out too much voltage with a bridge (I've learned that some capacitors smell like popcorn when they pop!). And I think it will be too low if I use a full-wave tube rectifier. Back to looking at power transformers for this project.
 
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IMHO, if you can find the 811-10 at much lower price than 300B then it's worth doing. Otherwise the 572-10 is a better option.

With the 572-10 you can use an existing 211 schematics as a starting point and maybe even definitive....This also means that lowish voltage can be done but is not ideal. You are just shifting the troubles from the output stage to the driver. You can get 16W clean in class A1 without going into positive grid with 1000V/70 mA and 8K transformer. You can use self bias, transformer coupling and possibly even RC coupling (together with self biased 572 only, IMHO) if you want to start with a simple driver and then upgrade it at second time. If your speakers have minimum impedance in the 5-6R range use 10K transformer with 75 mA as a starting figure.