Where is the trick as to be able to use this heater wiring method ??

[kagliostro]

There is a trick to apply as to avoid problem using this path for heater wires ?

Some guys do the thing in this way, does they have a secret trick as to avoid humm ??

Thanks

K

[FranciscoPerez]

Hi,
I think they just get away with that.
Your second picture looks like the way a soldano SLO is wired. I can't understand why they wire heaters like that in such a high gain design either, but they do elevate the c.t. and it seems to work well.   

[stratele52]

These wiring may induce hum in the amp .

[LooseChange]

Much less less likely to hum on the power tubes than the preamp tubes.

[kagliostro]

Much less less likely to hum on the power tubes than the preamp tubes.

That may be a clue, I didn't considered the fact that Power Tubes are less prone to admit Humm

Thanks

K

[alerich]

The Soldano SLO 100 is wired like that on the power and preamp tubes. The handful of SLO 100 amps that I have played all were relatively quiet for high gain amplifiers. Some normal hiss at higher gain settings but no more real hum. I read an article once online that explained why this approach would work (not that it was better or worse than the common method of tightly twisting the heater strand) but a quick web search for it was fruitless.

[dbishopbliss]

I saw this style of heater wiring for the first time on a another forum. The explanation can be found here.

[John]

I forgot till just now, but I think DL does his the same way, at least sometimes. I asked him about that, and he said when the runs are short it's much less of an issue (IIRC).

[stratele52]

If you think about it, a lot of the older amps, from the 50's and some from the sixty's had a single heater wire to the 12A_7's and the nine pin was grounded to chassis. 
 

Those amp are very noisy ( hum ) too . I modify the heater in two heater wire  with artificial ground ( 100 ohms to ground ) and they came quiet .

[HotBluePlates]

There is a trick to apply as to avoid problem using this path for heater wires ?

Some guys do the thing in this way, does they have a secret trick as to avoid humm ??

Much less less likely to hum on the power tubes than the preamp tubes.

LC gave you the answer. Basically, hum fields are more tolerable at output tubes where the signal level is much higher than in preamp tubes. Also, circuit impedances are generally lower, which reduces hum pickup.

I saw this style of heater wiring for the first time on a another forum. The explanation can be found here.

Their explanation is kinda B.S., but only to the extent that cancellation would only happen in the space between the parallel heater busses.

My first experience with this style of heater wiring was in a McIntosh MC-30, but while there are "preamp" tubes, the signal level is pretty high throughout as it is a power amp. That said, their matching C-8 preamp used untwisted heater wires, but they kept that relatively far from other wiring.

Bottom-line, we probably worry about twisted heaters too much, as there are many other ways to cause hum in an amp. But twisting heaters and keeping that wiring away from other wiring (and high impedance circuitry) does give you assurance that at least the wiring won't be causing hum.

[kagliostro]

Thanks to All

K