Grounding plan for OR120 clone

[focusbob]

Hi, I am building an Orange OR120 clone using the Weber 6O100 kit. I have attached their layout diagram. After reading about tube amp grounding schemes, including the excellent Hoffman grounding plan, I am concerned about Weber's suggested grounding scheme, which for example has all filter caps on the main grounding buss (which includes the preamp circuit) and which grounds each el34 to a seperate local chassis grounding point.

In trying to improve this suggested grounding scheme, making it closer to the Hoffman grounding scheme, I am having some difficulty adapting the Hoffman scheme to my (Weber's) layout. For example, I am having a hard time understanding where the "main board ground wire" begins and the preamp grounding points end. I'm also just doubting myself on any changes I come up with.

In general, how would you recommend modifying the suggested grounding scheme on the attached Weber layout?

A few changes that stood out to me, though that I am second guessing, are: 1) moving the power supply filter cap connection from the common ground buss to a direct connection to the PT grounding lug and 2) connecting grounds among the power tubes and running that line direct to the PT grounding lug. Do these changes make sense? What other changes would you recommend? Thanks!

[acheld]

The way I have organized this is to group the grounds for each separate each B+ node.

So, for example, if you have 4 nodes, B+4 would incorporate V1 and (usually) your tone stack and recovery stage(s), B+3 usually your PI, and so on back to your first node.  Those are your organized groups.

Then, decide where you want to ground each group.   I normally use a Hoffman derived plan, and so the high-sensitivity pre-amp group(s) get grounded at or near the input jacks (which I do not bother to isolate).  The remainder are normally grounded near the PT using a terminal strip.

For a simple amp, this really means your first stage and tone stack are grounded near the input, and everything else is near the PT.   However, more complex amps, such as some of the Dumble inspired amps I've been inspecting and building recently may need additional ground points.   To me, the organization remains the same -- eg, which B+ node serves the section in question.

There may be one exception to the above, and that would be a reverb tank.   The tubes for this might share B+4, but lately I've being grounding all reverb items at a single point at the reverb "out" connector.   I do not know if this is correct, but I have had a lousy track record of reverb related hum, and this approach seems to help a little.

Hope this helps, and I'd love to hear how others think about it.

[tubeswell]

Merlin Blencowe (a.k.a Valve Wizard)'s excellent 'daisy chain' galactic ground system for signal grounds. Each part of the circuit goes to a 'local grounding star' situated at the same point as where that part of the circuit gets its power supply (filter cap node) from. Each of local ground stars is located along the 'daisy chain' ground buss. The only point of this daisy chain that contacts the chassis is the input jack sleeve. The high current ground returns are all at the opposite ('floating') end of the buss. This stops the high-current returns from interfering with the low current returns (because the low current returns are closest to the chassis ground)

You expand this basic concept to accomodate more preamp stages