SE SV-811-10 power supply

[psherriffs]

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?

[audiowize]

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.

[w5jag]

Originally Posted by psherriffs

..... 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

[Lewis1]

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

[jdg123]

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.

[Lewis1]

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.

[audiowize]

Do you have the supply loaded while you're testing it? If you power things up without a load, the B+ will be too high. It shouldn't be so high that your caps fail though, that's an indicator to use higher rated caps.