wiring heaters...ugh

[Andy Le Blanc]

I think heaters are the only real chore with circuit dress.
I found some solid core bell wire at the local hardware store works.
The simplest thing I've found so far, is to use the pre amp heaters as the
cathode bias resistor for a pair of 6l6, one wire to ground through the
sockets, free DC heaters and simple dress.
Other wise its more a matter of practice, its easy to make a mess.
You could use a series string to ground, but the controlled warm up
will leave you impatient, the practicallity of your amp becomes more the issue.

[PCollen]

Sorry, but it's too loose at the sockets for the twist to be effective. This is hard to do and requires practice. You've got to maitain the twist all the way to the sockets. Loops at the end basically make that whole effort nil. I recommend 20 ga solid, which stays where you put it and is easy to thread into a noval socket. Everyone learns how to do this. You will, too.

Nice pic of exceptionally good (for that era) heater wiring in a '68 JTM50:

[ampdoc1]

Here is my buss setup.

[Ken Moon]

Sorry, but it's too loose at the sockets for the twist to be effective. This is hard to do and requires practice. You've got to maitain the twist all the way to the sockets.

I don't think that's correct. I'd love to hear some more expert opinions, but this is what I've gathered over the years.

The wires should be tightly twisted only when the two heater wires are together, but when they separate and go to the tube pins, they shouldn't be twisted.

I've even read that twisting two wires carrying the same signal reinforces the hum (actually makes it worse) - I haven't experimented enough with this to have an empirical opinion one way or another on that fine point.

Look at Merlin's pic again - the wires are twisted together only up to the point where the orange and blue wires separate - where there are two orange or two blue wires running together, they are not twisted:
[IMG761]http://i514.photobucket.com/albums/t346 ... ters-1.jpg[/img]

Here's how I do them:
[IMG519]http://i514.photobucket.com/albums/t346 ... eaters.jpg[/img]

As far as playonit's wiring, his preamp tube sockets are aligned such that it would be much better to use Merlin's method (going "up the middle" to pin 9), which would eliminate the big hum loop around the preamp tube sockets.

[Bob-I]

I think some folks are missing the point of the twist. Twisting itself is not really required, what IS required is that the wires need to be equal distance from each other. Running in parallel is the same as twisting which is why the SLO parallel buss is so effective.

[Ken Moon]

From everything I've read, the fact that the magnetic fields (generated by the AC currents in the heater wires) are forced to occupy the same physical space tends to cancel them out, or to lower their strength enough that they don't induce voltage changes in nearby conductors. (I've read more technical/mathematical explanations, but I think that's the basic idea.)

I thought I read something about the twisting itself being beneficial in a theoretical way, but I don't remember the reasoning.

I can see that a zip cord or bell wire, where the conductors are side-by-side, would have the same or similar effect on the magnetic fields, but what about the bus heater systems posted above, where the lines are in parallel, but maybe an inch apart? What if they were two feet apart? It would seem logical that the closer the bus wires are to each other, the more they benefit from being in parallel. Anybody know the maths?

The only drawback I see to the bus style is that you have to be more careful about the routing of all the wires that cross the heater bus - but it does look handy when the preamp tubes are arranged across the front of the amp, and there's no back corner to stuff the heater wires into.

[Dai H.]

the main thing might be the relative (physical) orientation to the other signal wires(loops) coming in, esp the sensitive ones. Keep the loops at right angles to ea. other sort of like on PCBs where you might have a jumper cross another trace at a strict 90 deg. angle. The little bit from the main twisted length to the tube socket would be in parallel but maybe factors such as the distance, and relative circuit position can make it more insignificant. The twisting should help keep the wires in a fixed physical position (where you want them relative to the other wiring). With the Soldano-style, the wires are thick and physically stiff(once straightened, fixed into position not going to move, or at least not easily). I once tried re-doing the heaters in a JCM800 since they weren't very tightly twisted, but afterwards I couldn't detect much of a difference.

[Phil_S]

Sorry, but it's too loose at the sockets for the twist to be effective. This is hard to do and requires practice. You've got to maitain the twist all the way to the sockets.

I don't think that's correct...

OK! I am guilty of not being precise in my words, which is why I posted the picture. The Chinese were correct, that a picture is worth a 1000 words. Thanks for putting a fine point on it. FWIW, I am in agreement.

All that said, I've seen all sorts of heater wiring that works just fine. Some of it is terrible, like in my 1966 Gibson Scout, where the wires are just simple short runs, no twist, no parallel, but it works fine. I've see pictures of builds using lamp cord (keeps wires exactly parallel). I've see those nifty pictures using the naked buss wire. Some people put them up in the air (what I usually do), and others put the twisted pair in the fold of the chassis (what we are looking at here). The point is that there are several ways to get a good result. Often, you won't know until you fire up the amp. It does, however, pay to follow one of the generally accepted proven methods to significantly improve the chances of success.

I think the main point of this thread is to respond to the OP by showing him what's typically done, and to show him what to look for. Like many neophytes, he did not "see" some of the really important details. I think we've done a darn good job with this!

[rp]

So no one has had any hum problems or any other negatives from the straight bus? The lazy guy in me is intrigued but I fear a probing disaster with all that bare wire.

[dynaman]

So no one has had any hum problems or any other negatives from the straight bus? The lazy guy in me is intrigued but I fear a probing disaster with all that bare wire.

Then use insulation.

[Ken Moon]

To Phil_S:

Sorry, Man! - my wording was way too strong - there are lots of ways to wire heaters that work, if you follow the basic rules of keeping signal wires away from heater wires, and make all crossings at 90 degrees when possible.

I was trying to make a fine point about twisting, and ended up sounding like an ass

Cheers, Ken

[Phil_S]

Ken
Not at all. I was trying to sharpen the OP's eye and was not nearly precise enough. You made some really good points and I was glad you did. It was more like, "Ouch, it hurts sometimes when you've got to admit you didn't quite accompish what you'd set out to do." Really, you were not at all disagreeable. I am sorry if I implied that. I suppose my reply was a bit of knee jerk.

All's well that ends well?

Phil

[playonit]

Ken
Not at all. I was trying to sharpen the OP's eye and was not nearly precise enough. You made some really good points and I was glad you did. It was more like, "Ouch, it hurts sometimes when you've got to admit you didn't quite accompish what you'd set out to do." Really, you were not at all disagreeable. I am sorry if I implied that. I suppose my reply was a bit of knee jerk.

All's well that ends well?

Phil

FWIW....this thread couldn't have come at a better time for me...When I saw it I screamed yeee hawwww... Learning a lot here... exactly what I set out to do by posting my pics... Wonderful knowledge and ideas presented. I will be better for it and have already dismantled and re-ran wires to follow the principles put forth here ....pic to follow.... Great stuff and a big thanks!!!!! Now let's see next topic... hmmmm Chokes anyone??!!!

[Colossal]

I agree with playonit; always great to see lively debate on these kinds of topics, regardless of one's level of personal experience. FWIW, I had only seen the "parallel buss bar" method of running heaters on Soldanos (and dynaman's wonder toolbox amps) but had, for some reason, only associated that method where a heater supply was pure DC. I wasn't aware that this was being used with AC supplies, so, very cool.

BTW, Ken and PCCollen, I did not construe either of your comments as having an adversarial tone.

[M Fowler]

Well I am going to try that buss wiring and if I get buzz your getting an eye full

Good discussion guys.