AB763 grounding scheme

[Roe]

It's not just the ripple voltage; decoupling of the stages is also important. The last filter is powering no less than six triodes, where two or at most three is usually considered the best practice. It's not quite as bad as it seems, though. Typically only one channel is in use at a time, so the worst case is it supplies four active triodes, and the phase relationship of the reverb recover stage to the others is all over the map. I find there are no issues with the one I built, and in fact the original circuit design and layout, random grounding and all, has been working pretty well for almost 60 years :^)

after rebuilding two, the noise decreased significantly

[martin manning]

after rebuilding two, the noise decreased significantly

Rebuilt how? What changes were made wrt the original?

[Oddvar R]

Yes, please?

[Roe]

after rebuilding two, the noise decreased significantly

Rebuilt how? What changes were made wrt the original?

I rebuilt the grounding and power supply, using merlin as a guide. One filter cap per preamp tube

[Oddvar R]

after rebuilding two, the noise decreased significantly

Rebuilt how? What changes were made wrt the original?

I rebuilt the grounding and power supply, using merlin as a guide. One filter cap per preamp tube

Could you be a bit more specific?

[nworbetan]

I can't help with the specific details as they pertain to rebuilding an AB763, but I'll second Roe's recommendation to read Merlin's grounding advice. He made the Grounding chapter of his his book about preamps downloadable completely free on his website.

http://valvewizard.co.uk/Grounding.html



This is a really easy follow explanation of where the current flows in the ground path, and why micro-managing current flow is important.

[Roe]

Rebuilt how? What changes were made wrt the original?

I rebuilt the grounding and power supply, using merlin as a guide. One filter cap per preamp tube

Could you be a bit more specific?

use multi-star grounding as defined by MERlin the tube wizard. see the excellent post above

[bepone]

moreover on this tip that every node must to have el.capacitor close to the valve which is supplying, it is a good habbit to think about plastic chassis. or how you can make amp in plastic chassis without humm . then if you do so, ground the amp close to input jack in one point and all is done.

[corkhead]

Hi,
I am the original poster, and I wanted to say thanks to all the contributors. The Grounding chapter a couple of posts up is a great find! Lots of excellent information there. My kit has made it to Australia, so it should only be a week or so until I have it in my hot little hands. I like the ideas and info posted. I will make a decision on which way to go with the build, and let you know how I go. Cheers all!