#124 Main Board Layout

[martin manning]

Trying to eat this elephant one bite at a time, I took a shot at the #124 main board layout and wiring using the excellent resources here, including ic-racer's schematic and the linked ods photos and notes.

I think I have most of it figured out, but there is some uncertainty about the grounding of the overdrive cathodes and the PI (as noted in the schematic). The photos clearly show two brown, one green and one black wire exiting the board in this area (where the question marks are in my layout).

I'm guessing the black is the OD cathodes going to ground 1, but either way I can't figure out why there are two brown wires. Also, there is an eyelet on the board that is in use, but the leads are under the board.

Anybody worked through this? Any insight will be appreciated.

MPM

Edit: Drawing removed; see final version.

[jelle]

The ? eyelet is a tie point for the master signal that comes from the relay and goes to the loop jack outlet.


jelle

[martin manning]

I can see the brown wire coming from the front panel... It comes from the wiper of the master, though, not directly from the relay, right? So that is one of the two brown's entering the hole in the board and going to the ? eyelet, and the other one is just the master signal leaving (from the ? eyelet)?

Seems like that lead could run all the way back to the loop jack without the tie point, and I've wondered why it isn't shielded, since it goes all the way from the front to the back one way or another.

Then the black must be the PI ground. Which still leaves the mystery of where the V2 cathodes are grounded...

MPM

[Guitarman18]

jelle wrote:

The ? eyelet is a tie point for the master signal that comes from the relay and goes to the loop jack outlet

On an HRM, the wire would come from the relay but on NON-HRM (as #124) it comes off the wiper of MV.

V2 cathodes were grounded in different ways, often by daisey chaining then to presence cap ground and V1 grounds I believe.

[talbany]

Not that it matters much but this is the design I favor with quite a few changes.. First instead of the 100K 1.5's I prefeur the 250K 3.3 or 180K 2.7 with 150K 2.2 with 5uf bypass caps..little smoother to me.. a .047 mid cap... tonestack wired like a Fender.. If you want the mids lifted either a 50K or 100K pot if you use the .002 midlift w/390 on the front I would go with the 50K.. For the Od the same 250K or 180K w/ 150K 5uf's as well... a 50K or 100k Trim pot... I like the 50 with a 470k..180K and 4.7k tail.. For the OD entrance. a 100k resistor feeding the level and a 180K feeding the Ratio...For the PI 470 ohm for cathodes a 15 or 18k for the PI Tail. NFB 25K pot w 4.7k refrence and 100k fom the 4 ohm tap..w/ 1uf electolytic... For the boost if a client plays a Strat I lift the Stack about 47K if He plays Humbuckers I break the Bass pot and lift the stack to taste.. 33k-68k... That's my fave right now.. If anyone is curious..

Tony VVT

[ic-racer]

One way to imagine it.

My picture shows the brown wire comes from the MV and routes under the boards to the isolated eyelet. From here the brown wire loops through the hole with the other wires and follows the green and black wires to the back panel, eventually to the send/return jacks.

You can see on the overtone layout that he Nik was not sure what was going on there either, and just looped a v2 cathode ground wire through there.

[martin manning]

Thanks for the replies guys. talbany, that's some dense post... it'll take me a bit to digest it.

I updated my layout to reflect the comments above, and speculated that the V2 cathodes are taken back to the OD trimmer and then to the V1 cathodes under the board and finally to ground point 1. Looking closely at the ground lug of that trimmer, it looks like there are a couple of other wires in the eyelet with it.

I think it would make most sense to take the PI ground back to ground point 2, and there is a black wire in the bundle going back to the loop jacks that may have originated at the PI tail.

If you look closely at the isolated eyelet it does appear that there are just two wires soldered there, and their ends are bent back towards the incoming brown wires.

I'm still a little puzzled as to why the MV signal needs a tie point on the board at all, and why this lead and the return from the FX loop wouldn't be shielded, given the treatment of the other long signal wires. Any thoughts on this, generally speaking?

MPM

Edit: drawing removed; see final version

[ic-racer]

Looks great. You are right, that brown wire would loop through the hole twice to match the pictures. My speculation on the single eyelet is that is just that it would keep that wire attached to the board so it could be hooked up with the rest of the wires attached to the board or to be able to put the cable ties on that wire bundle during board construction.

Be sure to indicate the 500k trimmer measured about 350k.

Is your board drawn to scale?

[martin manning]

Thanks! The drawing is not to scale. I started by tracing the sketch in the notebook photo, and then went through the schematic and pictures to tweak it into shape electrically and physically.

I've updated again to reflect comments. Thanks for all the input... one down four to go.

MPM

Edit: Corrected B+4 wire color to orange.
Edit2: Drawing deleted; see final version.

[ic-racer]

The Rectifier/Bias board and 12v supply board are very similar between #40 and #124. This #40 layout is roughly to scale and may be of some benefit to you. The FET on #124 was on a PC board. Otherwise, the FET board in #40 is also somewhat similar.

https://tubeamparchive.com/download/file.php?id=5191

[talbany]

If Someone has an accurate layout or schematic of the Skyliner stack of 124 I'll be glad to finish this Visio of the entire amp with the layout posted by martin. exact wire color and all...This way we can start with 124 and people can revise the visio to whatever mods they have done and liked..


Tony VVT

[ic-racer]

Schematic is here: https://tubeamparchive.com/viewtopic.php?t=5719
I wired mine straight from the pictures, so I never made a layout.

That schematic should give you what you need to finish the layout. Note that the RadioShack 6-0-6 really produces 12v, what you need to show is a 3-0-3v for the #124 circuit.

This public domain Ceriatone Overone layout shows a correctly wired Skyliner nearly identical to #124. Some values may be off, so use the values from the #124 schematic.

[talbany]

ic-racer

Thanks will do.. I remember the sketched layout Gill posted along with the amp... but was not sure if it was drawn correctly.. I think I remember it not being quite accurate with the pics Maybe Gill can chime in here and give some validity to the layout tell me I am wrong.. Thanks again



Tony VVT

[ic-racer]

It would be cool if you could nail all the #124 values exactly. There are plenty of layouts with various modifications of #124 out there already, but none to date show it exactly as it should be.

[martin manning]

ic-racer, thanks for the link... it is sometimes hard to keep track of where everything is here. That rectifier/bias supply board is a Fender twin, yea? Goes back to 1964, or there about.

Looks like we have a community project going here for a layout, eh? Cool. Note that I corrected the color of the B+4 wires on the main board layout above to orange.
Here's the PS filter board as I make it out.

MPM

Edit: Amended notes and colors.