Filament / heater wiring tech

[CoffeeTones]

Hello, is there technical reason or electrical benefit that in many amps, especially Fender and Dumble style amps with overhead / floating heater wiring, the heater wires are twisted but then are left parallel instead of twisted, right up to the socket pin terminal?

Given room for twisting, wouldn't twisting be beneficial?

[Stevem]

You can twist them up as much as you have the mental composure to deal with working with them that way, but getting them any better than in your photo is a waste of time!

When it comes to amp wired up like in your picture what gets you the most bang for your buck and time is to use a first gain stage tube that has a twisted filament, as its only in gain stages where the signal level is less then the AC filament voltage where 60 hz hum needs to kept at bay.

If you want to go to town you can strip out good Mic cable for its braded shielding , slip that over the long lengths of the heater run, solder jumper from section to section, heat shrink those sections and then ground that back at the PT ground point .

[JazzGuitarGimp]

If you're asking if the the two red wires (or the two blue wires) going down to the socket should be rwisted, the answer is no, it's not necessary, and gives no benefit. Twisting the horizontal pair (one red and one blue) reduces the electro magnetic field the pair emits because the magnetic fields of the two wires are 180 degrees out of phase with one another and by twisting the pair, a good amount of the EMF cancels itself out. The two red wires going down to the socket are of the same phase, so twisting them does nothing as far as EMF phase cancelation goes.

[CoffeeTones]

If you're asking if the the two red wires (or the two blue wires) going down to the socket should be rwisted, the answer is no, it's not necessary, and gives no benefit. Twisting the horizontal pair (one red and one blue) reduces the electro magnetic field the pair emits because the magnetic fields of the two wires are 180 degrees out of phase with one another and by twisting the pair, a good amount of the EMF cancels itself out. The two red wires going down to the socket are of the same phase, so twisting them does nothing as far as EMF phase cancelation goes.

That is the information I was seeking. Is there any harm in twisting the two red and / or the two blue wires all the way to the socket?

Thank you!

[Phil_S]

Is there any harm in twisting the two red and / or the two blue wires all the way to the socket?

What you are asking about is actually very challenging to do and it will have no benefit. The wires are neat and parallel, and that has the same basic effect as twisting. Twist to that small length will create more bulk and make it more difficult to work at the socket. To be direct, there is no actual "harm" done by twisting them, but you'll find out quickly that you'd rather not do that.

[JazzGuitarGimp]

Hi Gerald,

You're welcome. There is no harm in twisting the red/red or blue/blue pairs to the sockets. I think most people wouldn't do it just to save time.

I have noticed the same with regards to twisting PT & OT windings; some people do it, and some do not. Personally, I do. I figure the more I can do to reduce any and all stray electromagnetic fields in the amp chassis, the better it will be. You should not include center taps in the twisted pairs for two reasons; 1) They are usually kept steady at one potential (ground) or another (B+), and 2) Including them will interrupt the desired symmetry in the twist.

Cheers,
Lou

[CoffeeTones]

Thanks for the replies and sharing of knowledge and advice.

[pdf64]

...with regards to twisting PT & OT windings; some people do it, and some do not. Personally, I do. I figure the more I can do to reduce any and all stray electromagnetic fields in the amp chassis, the better it will be. You should not include center taps in the twisted pairs for two reasons; 1) They are usually kept steady at one potential (ground) or another (B+), and 2) Including them will interrupt the desired symmetry in the twist...

My thinking is that it's fine to include a CT in a balanced pair twist, as any dc reference on the CT won't affect the radiated ac field, eg the CT wire is effectively 'invisible'.
The CT of an OT primary will have ac ripple on it, but that will be common mode to all 3 wires, so best to keep them together (eg in the twist) away from sensitive areas.
I suppose there's a slight drawback, in that 3 wires can't be twisted as tightly as 2.

Regarding heater wiring to 9 pind sockets, I think Merlin has the best method http://www.valvewizard.co.uk/heater.html

The Merlin method has RJ's seal of approval! https://tubeamparchive.com/viewtopic.ph ... c&start=15

[CoffeeTones]

I've tried the Merlin approved heater wiring and it would be fine in some cases, however in other cases it is not so good. For example, if you have a parallel wired preamp tube, an EF86, or even a cathode follower with it's socket mounted plate resistor. With those, it is too bothersome and too close to some sensitive parts. I really don't care for the Merlin approved heater wiring when it closely crosses with the jumper from pins 3 and 8 on a long tail phase inverter tube either. IMO, the Merlin approved wiring seems great if you only consider using it in a way that is similar to the picture.

In future builds, I'm considering a combination of the Merlin approved version and the Fender, overhead version. This will keep the long runs against or in the corners of the chassis and then raise the wires that jump over the tube, in order to avoid the situations I described above.

Obviously, the Fender, overhead version gets away from everything, but does not use the chassis for shielding. Other versions that do use the chassis for shielding, cause you to run wires over the heater wires, unless you have a layout that allows you to not have any wire circling around to the rear of the tube. Compromises.

[Malcolm Irving]

Not saying this is the best way or anything, but I’ve ‘evolved’ towards the following:

The V1 tube is easy to wire with a tight twist for the heaters (because there are just two wires to deal with, not four). At some point I got slightly worried about the current rating for a single daisy-chain, and started to run two ‘parallel’ daisy chains (with odd numbered tubes in one chain and even-numbered tubes in the second chain). Now both V1 and V2 become ‘easy to wire’.

Keeping in mind that for some configurations, when the volume is turned down, V2 can be just as much a source of hum as V1, this becomes a useful feature.

Finally, I’ve found that from V3 onwards twisting is not necessary. I just run the two wires touching each other and held together by cable-ties. Then V3 and the rest become easy to solder as well.

[xtian]

Nice practice, Malclom. Can post photos?

[Malcolm Irving]

Next time I have a chassis out of its cabinet, I'll take a photo.

[pdf64]

I've tried the Merlin approved heater wiring and it would be fine in some cases, however in other cases it is not so good. For example, if you have a parallel wired preamp tube, an EF86, or even a cathode follower with it's socket mounted plate resistor. With those, it is too bothersome and too close to some sensitive parts. I really don't care for the Merlin approved heater wiring when it closely crosses with the jumper from pins 3 and 8 on a long tail phase inverter tube either.

Not sure what is meant by a parallel wired preamp tube?
With an EF86 and other 6V heaters across terminals 4 & 5, why not mount the socket rotated 180 degrees?
Socket mounted resistors and links can just loop over the heater wire to terminal 9, allowing plenty of clearance.
And such DCCF and LTP are generally 2 or more stages along from the input, so making these things a bit less stringent.

[CoffeeTones]

Yes, the EF86 could be worked out fairly easy. IMO, looping any resistors or links across and above the heater wire is not much different from looping the heater wires around the tube, it seems to recreate the hum loop that we were trying to be eliminate in the beginning.

Below is a parallel wired 12AX7 example.

[TUBEDUDE]

I have always twisted the heater wires, tightly as possible. It seems, at least intellectually, that the wires run parallel will emit some of a electromagmetic field as the wires don't occupy the same exact space, just close. Must be good enough though, if folks are using it with good result.
In my last build I twisted the xfmr heater leads and soldered them to the octal sockets. At the last octal, I connected two balancing resistors and tied them to the output cathodes to elevate the heaters. After this, I experimented by continuing the string through the Noval sockets with small gauge silver coated copper with Teflon insulation. I pulled the wire through the pins eyelets, carefully stripping the Teflon at the eyelet to solder, then twisting tightly to the next socket, pulling the wirewire throught the 9 pin, and the 4n5 pin combo l, stripping.....etc. (Hopefully you can see this in the picture) Not sure if it was overkill, and a coincidence, but this is the quietest amp I've ever heard. Unfortunately my curiosity is not great enough to get me to strip and rewire the amp to see if another scheme is as good.