Best practices - transformer lead dress

[Lindz]

I'm working on a high gain build (SLO derivative) and would appreciate input from folks in the know about best practices for PT and OT lead dress

Several questions below - I have searched and done a lot of looking at various builds but get varying opinions and thought I would post to see what folks think.

OT - Should I twist primary leads and center tap together or just twist primaries? If I just twist primaries is it good practice to bundle the center tap with them, or better to run it separately and away from them?

I assume I also twist OT secondaries.. again should I twist the common with them or run/bundle it separately?

This layout has a fairly long run for the secondaries to the tubes (between 9 and 13 inches depending on how I rout it)

I can run them under the board about 3" away from the tubes and 1-1.5" away from most of the caps and signal components (9" run in total), or I can run them a little further around the back edge of the chassis for about 12" and get no where near the board except where it enters the chassis. If I rout that way they would pass parallel next to (or could be bundled to) the primaries and under the speaker jacks for about 5 inches along the back of the chassis (or I could move them apart somewhat).

Is running OT primary and secondary leads parallel to each other or bundling primaries and secondaries good practice? How about bundling the primary b+ with either or both?

PT - I am thinking I should twist the HV leads but not sure about bundling the or twisting the center tap with them?

Heater leads - again twist but what about center tap? bundle or twist with them until the ground point where the heater leads would continue on twisted to the tubes?

AC mains - I am thinking I should twist from the IEC jack to the switches and rout away from everything else against the edge of the chassis as possible. Since I have a 6.3v lamp is it good practice to bundle the 6.3v AC with the 120v AC or move them apart? I assume I should not twist them all together?

Leads from choke - twist? Should I be concerned running them by or over any AC? if so - parallel or perpendicular?

Footswitch - this amp has a shorting footswitch that switches several LDR's for channel switching. There is also a shorting toggle switch on the front panel with a pretty long run to the jack and switching points on the board. Should I twist those leads? Should I keep them away from signal, AC or DC runs? How about bundling along with the OT primary and secondary along the back of the chassis? I could also run it under the board no where near any of them?

Footswitch jack - schem calls for grounding using switchcraft shorting jack with crush washer to chassis. Any issues using an isolated jack? I thought using an isolated jack might give me more control as to the ground point in case of loops

Fuzzy picture below from my cel phone of partially complete build - should give you the idea. PT on left under cap board, OT on right at right end of chassis. OT primary leads red and blue shown twisted behind board, b+ currently runs along edge of chassis at back separately. OT secondary leads shown run along back by jacks at right rear

[martin manning]

I just twist filament leads and bundle others as needed to get a neat result. Below is an ODS with everything bundled together, including primary leads from the relay transformer. No issues.

[Leo_Gnardo]

What Martin said, and (it should go without saying but I'll say it anyway) keep OT leads away from your input circuits to prevent ultrasonic or RF oscillations.

I do more repairs than building but it's evident that even some big name & boutique manufacturers have trouble with this. On occasion I've sectioned off the interior of Mesa/Boogie amps with sheet copper, to keep the input from "seeing" the OT leads sprouting out of the chassis only a couple inches away. Without the copper shielding, lots of "blocking" from ultrasonic noise, and the wrong kind of distortion.

There's also the case of an early Fargen (s/n 7) where he parked the most sensitive part of the circuit (dry/rev mix point similar to Fender's) right on top of the OT leads, less than half an inch away. It didn't take much gain to set this amp into constant ultrasonic oscillations that might be entertainment for dogs & bats. I made a shield of grounded copper foil sandwiched between sheets of fish paper and slid it under the circuit board in the sensitive area, then the Fargen started to behave itself (and sounded mighty good too). Since then I hope Mr Fargen has figured out what and what not to do.

Say Lindz how's that 3D printer going? Have you gotten any interesting assignments for things to build?