ODS #183 Build

[ijedouglas]

True, but either way will work just fine. The the main power supply board pattern Pfarrell is using has B+2 and B+3 grounds merged and routed to be grounded with the power tube cathodes.

I have not tried it both ways in an amp but when chatting with Jelle a while back he said there is a difference. I couldn't tell what, but in my 183 and BM I used layout with screens between power tubes and V3/2/1 at input.

[martin manning]

From a ground current return path point of view, it makes more sense to put the PI filter ground closer to the power stage, and close to or coincident with the PI cathode ground to form a local star. That's my standard practice, but from experience I find it does not hurt to ground the PI filter with the preamp filters at the input jack ground.

[rootz]

From a ground current return path point of view, it makes more sense to put the PI filter ground closer to the power stage, and close to or coincident with the PI cathode ground to form a local star. That's my standard practice, but from experience I find it does not hurt to ground the PI filter with the preamp filters at the input jack ground.

Second that practice. But might it be Martin, that signal levels are rather high around the PI, but return currents low, so that any ground potential difference would not matter much in the first place? Or am I seeing this the wrong way? I think I don't fully get the mechanisms at play here.

[pfarrell]

Getting sorted.....I'll probably steal Ian's move and add some tabs to support the grid resistors...

PF-183_16.jpg

[martin manning]

Isn't that cute! Little pink bows ;^) Good to see the all-radial-cap eyelet boards are working out for you. Did you get all the grounds sorted out?

[pfarrell]

Ha! Martin, that’s something (the pink bows) that I stole from the airline industry…where I understand that the zip tie isn’t used due to the fact that they degrade…wire and cable are bundled with that binding “string”… I’m not sure of its composition, it’s got a little tooth/wax? to it and doesn’t want to slip very easily when you knot it.

I think I understand the grounding…and your eyelet board work is awesome…

Oh, is this the first "all-radial" cap 183 build?

[martin manning]

There a problem here. Transformer HT leads (Black and Blue) go to the eyelets nearest the board mounting screw, top eyelet goes to the HT ground, and the B+ comes off the bottom eyelet.The yellow wire (HT CT) is not used. The green bias winding ground should go to the HT chassis ground lug, along with the bridge rectifier ground.

Note you could run the yellow HT CT over to the reservoir caps (middle of the stack, junction of the balance resistors), and then you wouldn't need the balance resistors anymore.

Oh, is this the first "all-radial" cap 183 build?

This is at least the first one I've seen built from those board drawings.

[martin manning]

A couple more corrections- see below for the reservoir capacitor and B+2 ground locations. The other ground on the filter board (B+3, 4, 5, nearest the front of the amp) goes to the input jack ground lug. Your relay supply board ground is correct, but the foot switch jack ground goes there too, all the way from the XLR/DIN jack. It looks like you have the B+3, 4, 5 ground routed there.

[pfarrell]

Martin! Thanks for the inspection... really appreciate that.

I re-read everything several times—and I could interpret things in more than one way (I know, I know)—I think it's easier for virtual diagnosis If I tell you what I think you are saying? I'm using the ground points as labeled on the #124 layout drawing for clarity (per earlier in the thread, attached below).

Rect/Bias board:
—I believe the HT (blue and black) wiring is correct—see this angle below—per 100W Marshall PT eyelet notes and coming off the centers of the diodes, Ian fished for clarity here earlier in the thread (appreciated!!!) when I adjusted the bias board wiring.
—Add a ground leg from top right eyelet of bias board to GND 4 (same point as Bias Gnd from bias board) / move green bias ground from transformer to GND 4
—Bottom eyelet is the B+ running to the main power board (B+ Rect)—which I believe is correct—but hard to see in previous image.

I'll disconnect and bundle the HT CT (yellow).

Main Power Supply board:
—B+1 Gnd (grounded to point near bias board, GND 4 on #124 layout)
—B+2,3 (ground point between first 2 pwr tubes—GND 3 on #124 layout)
I think both of those are correct—but unclear in the photo I posted.

The other ground on the filter board (B+3, 4, 5, nearest the front of the amp) goes to the input jack ground lug.

That ground I don't see on the board as labeled? It's "B+4,5" See pic. I'm thinking the confusion here on my part is the labeling on the drawing—where I'm reading the number after the comma as the GND number per the #124 layout... I'm thinking that's wrong! and am now getting some good learning clarification...

So, "B+4,5" should go to GND 1? I'm now seeing that per the #183 layout drawing as well...

Much gratitude!!

PF-183_17-HT.jpg

Screen Shot 2022-07-26 at 8.23.57 PM.png

[ijedouglas]

Main Power Supply board:
—B+1 Gnd (grounded to point near bias board, GND 4 on #124 layout)
—B+2,3 (ground point between first 2 pwr tubes—GND 3 on #124 layout)
....
So, "B+4,5" should go to GND 1? I'm now seeing that per the #183 layout drawing as well...

Correct.

[martin manning]

The B+4 and B+5 ground goes to ground 1, at the input jack. The B+2 and B+3 ground goes to ground 3, the power tube cathodes. I miss-typed above.
Your read-back of the rectifier bias board corrections sounds good.

[martin manning]

Edited the ground description (here: https://ampgarage.com/forum/viewtopic.p ... 98#p443098) to include all chassis ground points.

[pfarrell]

Power section pretty close. Ran out of matching 1R resistors... obviously have to run heater wires... was able to scrounge the switches and pots—used some up in the Trainwreck builds that I forgot to account for! Thanks for all the help guys.

PF-183_18.jpg

[martin manning]

At this point, making sure no DC can short to ground, I would be tempted to apply some low voltage AC to the IEC inlet through a light bulb limiter, and see if all three power supplies are functioning. With 12VAC going in, you should get roughly 10% of the expected voltages, or about 50V on the HT and on down the power rail, -5V on the bias supply, and 1.6V at the regulator input. If you do this with a Variac, you could slowly run it up to full line voltage, and then be confident that the power supplies are solid.

[pfarrell]

Good advice Martin. I do have a variac....