I have seen some fenders as well as fender type kits with the heater wires above

[catnine]

 Some have the heater wires twisted but some have them above the tube sockets then drop down and other have them against the back side on the chassis and on the chassis . I don't know what I used for reference but I always laid then down before any other leades and twisted them and had them against the chassis tucked against the back edge and kept the leads so pin 7 on one tube went to pin 7 of the next and did the same with pin 2 and did the preamp tubes so they if I recall pin 7 of the output would go to pin 4&5 can't recall off hand may have been 2  to 4&5 . I have seen 5E3's above and down on the chassis . My SF champ build uses a tweed style chassis yet there was no way to have the hears leads above the sockets without them in the way or to close to the eyelet board and running them right over of near the output jacks so I ran them on the chsssis toward the back of the amp. Somewhere I read that placing them on the chassis allowed the chassis to act like a shield of sorts.

 My point is , is there a prefered way or proper way or does it even matter?

[eleventeen]

SF Champ (as mfd) grounds one side of the heater winding and one side of all the 6.3 v heaters and runs only one wire for heater power to all the tubes (except obviously the 5Y3) This was probably done out of cheapness and most Champ upgrades have either the up-in-the-air typical Fender style or against-the chassis style. Either appears to work well and lower AC hum in the output. If the PT has no center tap on the 6 volt winding, the artificial center tap deal with the 2 * 100 ohm resistors will be called for. A friend of mine just did this to a SF Vibro Champ I gave him and it made a noticeable difference.

[HotBluePlates]

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[catnine]

SF Champ (as mfd) grounds one side of the heater winding and one side of all the 6.3 v heaters and runs only one wire for heater power to all the tubes (except obviously the 5Y3) This was probably done out of cheapness and most Champ upgrades have either the up-in-the-air typical Fender style or against-the chassis style. Either appears to work well and lower AC hum in the output. If the PT has no center tap on the 6 volt winding, the artificial center tap deal with the 2 * 100 ohm resistors will be called for. A friend of mine just did this to a SF Vibro Champ I gave him and it made a noticeable difference.

 I know all the three SF champs I had, had the one 6.3 wire and grounded the pin 4&5 on the preamp to the chassis same deal with the music master bass amps . to save money. many tweeds and later SF and BF larger amps had the twisted pair . I have not seen many fender chassis on the inside. I can't recall what the 67 BFSV I had was I never had a reason to open it up. At the time if I had I wouldn't know what I was looking at anyway. THe SF champs I had were not noisy with hum yet there is not much in them so perhaps they could go without the twisted pair and it worked fine. Mine never gave a cause for concern . Even the 6G2 had the one heater wire scheme , it was later when they went with the twisted pair . I saw some video a few weeks back filmed in England think it was a marsh kit building a 6G2 and the instructions clearly showed the heaters over the tubes sockets yet the three fellows built theirs with the heater leads twisted but on the chassis at the rear.

 There was no way I could hang my heater leads above the tube sockets in my P-P princeton build they would have been right over the output jacks and right over the B+ on the eyelet board so I ran then on the chassis and at the back and have no hum . I didn't have the room since my chassis is not as deep from front to back as the princetons were. You work with the room you have.  

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[catnine]

Some have the heater wires twisted but some have them above the tube sockets then drop down and other have them against the back side on the chassis and on the chassis .

Heaters wires in original Fender amps was down on the chassis and tucked in the corner at the lip in a tweed chassis, and up in the air in 60's brown/white/blackface amps.

Each kept the heaters as far as possible from the circuit board and its components, given the physical arrangement of the tube sockets vs the board.

[catnine]

... I saw some video a few weeks back filmed in England ... the three fellows built theirs with the heater leads twisted but on the chassis at the rear. ...

Almost everyone blindly copies whatever amp they're used to looking at.

Marshall lays their heater wires against the chassis, not the way Fender did it. I'm sure the Brit guys were copying the Marshall amps they're used to looking at.

 This is my chassis



 You can see how there was no good way to run the heater leads over the sockets. It worked fine. Since the amp has the off/on switch next to the pilot lamp and my output jacks are between the output tubes I had to go around the far left of the PT or the heaters would have been over the AC line and over the OT primaries and secondaries and real close to the eyelet board . If the eyelet board where smaller like the princetons had and the power switch were at the rear and the output jacks at the back then I could have gotten away with it. Plus they would have to clear the 3 watt screen resisters which the princetons did not use and the droppers were at the left end of the eyelet board off a cap can . It was to close to risk it in my build.

[Cups]

Traynors do the "over the socket" style loop. They tend to be hummy amps but I don't think just the heaters are to blame.

The Sunn I worked on had the heaters untwisted bundled up with signal and power wires. These amps are hummy too. I rewired the heaters in twists and did other things and it resulted in a much quieter amp.

I just traced a Harmony model 305 and instead of ground referencing the usual way they referenced the heaters to the power tube cathode. Never seen this before. Have no idea if the amp is hummy. It arrived dead and is getting a rebuild. Probably hummed like crazy looking at the crazy random grounding.

[Cups]

I should clarify how the Harmony was wired (I can foresee some questions) :
It was wired at the cathode pin (pin 8) and I'm assuming it's using the cathode resistor/bypass cap as a ground reference.

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