Two-Way Run Inside Shielded 4-strand Cable?

[Lancer X]

I am building the 5E3MM "Mod" version of Rob Robinette's  Deluxe Micro amp design.  I have a question, if you'd be so kind:

There are a couple preamp options in this design, which are controlled by 3-way switches.  I am planning to run shielded Canare L-4E5C quad mic cables from the board to switches on the front panel.  In each cable, one of the 4 wires would run from the cathode to the switch, and the other three wires return from the switch to the three different options out to ground.

TL;DR:   My actual question:  is it okay to have a ground path wire both sending and returning within the same twisted quad cable? 

Guessing it's okay since this isn't signal and is just a grounding path??  Or could my design create a cross-talk problem?

[sluckey]

You don't need any shielded wire to switch resistors and/or caps on the cathode.

[Lancer X]

I'm using shielded wire because the switches are closer to the power section and the wire is a long run from the preamp tubes.

Thoughts about the cathode ground wire running from and back within the same twisted quad-conductor wire?

[sluckey]

I'm looking at Rob's schematic. What you propose will work but seems a bit awkward and unnecessary to me.

[Lancer X]

I'm looking at Rob's schematic. What you propose will work but seems a bit awkward and unnecessary to me.

Perhaps a picture is worth a thousand words - see attached.  I have used RobRob's board layout for the "vanilla" Deluxe Micro and simply added more eyelets to accommodate the extra resistors and caps for the switch options.  My shielded quad-cable scheme was an effort to accommodate the board layout as-is.

Eyelets 1-3 are the three possible Bypass mod paths:
1)  From switch to "Normal 5E3" path to ground
2)  From switch to "2.7K with 1uF bypass cap" path to ground
3)  From switch to "Unbypassed 2.7K cathode resistor" path to ground
4)  wire from V1A cathode, then wire continues out to Bypass mod switch.

Shielded cable allows me to fly a single wire from the board to each physical switch on the front panel, while avoiding noise generation.

Same thing with the Negative Feedback Loop switch:
5)  From switch to "Normal 5E3" path to ground
6)  From switch to "no cathode bypass capacitor" path to ground
7)  From switch to "Feedback with no cathode bypass capacitor" path to headphone jack
8)  In from V1B cathode, then out to NFB switch

I hope this explanation makes sense.

How would you propose to tackle this situation?

[sluckey]

I would do the bypass switch like this. Components neatly arranged between the switch and the MV ground lug. Single wire direct to tube socket.

[Lancer X]

I would do the bypass switch like this. Components neatly arranged between the switch and the MV ground lug. Single wire direct to tube socket.

Thanks!  I'll see if I've got available real estate for this layout tonight!  Shielded single strand for that run to the tube?

Hmm, the NFB switch will have a second wire to the output section though.  Hmm...   

[sluckey]

I would do the bypass switch like this. Components neatly arranged between the switch and the MV ground lug. Single wire direct to tube socket.

Thanks!  I'll see if I've got available real estate for this layout tonight!  Shielded single strand for that run to the tube?

Hmm, the NFB switch will have a second wire to the output section though.  Hmm...   

You can use shielded cable but it's really not needed. Connect the shield to the MV ground lug only. No need to connect the shield at the tube socket.

As for the NFB switch, think about it for a bit. You'll find a good simple solution. No shielding needed.

I just realized that I put a NFB label on the bypass switch. You knew what I meant, right?   

[Lancer X]

I just realized that I put a NFB label on the bypass switch. You knew what I meant, right?   

Yep - no worries.  Your layout makes me want to build this amp as point to point (Rob created a layout for that.)

Doesn’t really make sense with this combo cab though.  Maybe a future project if I love this one. 

[Lancer X]

Well, with respect to real estate, turns out I ain't got none.     Never realized these full size 3-position switches were going to be so chunky!   They almost didn't fit.  This pic before doing some shaving...   

[sluckey]

This switch would have given sufficient room...

     https://www.tubesandmore.com/products/switch-carling-mini-toggle-spdt-3-position-solder-lug

[Lancer X]

Yes, sir - live and learn.