Heater Wiring

[FourT6and2]

Out of curiosity, can a kit be wired using bus wire for the heater wiring a'la Soldano SLO instead of the typical coiled/twisted wires? Or is there a technical reason (other than tradition) why it's not done this way in Marshalls? I'm guessing because on Marshalls the orientation of the tube sockets prevents the necessary pins from being in-line with each other?

http://www.c3amps.com/Photos/SLOBuildLo ... roPots.jpg" onclick="window.open(this.href);return false;

http://www.c3amps.com/Photos/SLOBuildLo ... Atube1.jpg" onclick="window.open(this.href);return false;

http://www.c3amps.com/Photos/SLOBuildLo ... /Bias1.jpg" onclick="window.open(this.href);return false;

It's just that the wiring on SLO's is so amazingly clean. I'd like to build my kit (when I get it) as cleanly as possible.

http://www.c3amps.com/Photos/SLOBuildLo ... s/xall.JPG" onclick="window.open(this.href);return false;

[OnTheFritz]

I don't know squat about Soldano's but maybe the PT provides DC to the heaters, as opposed to AC in Marshalls.
The wires are twisted to phase cancel out hum from the AC.

[FourT6and2]

Well, what about the other wires connecting the various pins of the tube sockets for both the preamp and poweramp? In Marshalls, the wires are all routed out and away from the sockets and then back toward the next socket. For example, the wire connecting Pins 6 of V4-V7 on a Superlead circuit. On an SLO a straight bus wire is used to run across all the tube sockets. It just looks so much cleaner and gives you more room to work.

And I'm pretty sure that the PT in an SLO carries AC as well...

I just found this in another thread here:

"They use AC. They kinda get away with it because the heater wires are equadistant from each other, and are pretty straight, but.... since sensitve wires like high impedence signal wires are in the middle of them, capacitive (AC) coupling can be an issue, so it is best to tightly twist heater wires when you are using AC, and tuck them away from any signal wires."

But I still don't understand. If it's still "best to twist heater wires together," why can Soldano get away with it? Weird.

[FourT6and2]

Another thread about the same thing: http://forum.metroamp.com/viewtopic.php ... 11&start=0" onclick="window.open(this.href);return false;

[demonufo]

There is enough of a gap between the wires to avoid back EMF causing any issues on the soldano, but I personally feel that there are too many close parallel runs going on in the power tubes, and this could be improved on. If there is enough gap between the heater lines they won't need to be twisted since they won't be interfering with each other in the same way, provided that they are kept at an equal distance.
The reason we twist heater wires is not to stop them from inducing noise in other wires, it is to stop them interfering with each other via back EMF, amongst other reasons.
If you imagine an electrical current carrying wire giving off a magnetic pull when it is energised, and another electrical current carrying wire 180 degrees out (effectively what is happening with single phase AC) which gives off a magnetic pull in the direction it is going, the magnetic pull from these two wires inhibits the flow of electricity to the other wire. Making it a difficult load, and prone to hum, since the transformer has to work harder to get the required current to flow.

I do like the soldano preamp method though, it's just that you would have to orient the preamp tubes slightly differently in order to do that in a marshall, but the marshall method is still better IMO.

The Marshall way isn't that bad in practice, it just isn't pretty.

Now if you're talking Hiwatt...


That's what I call tidy. AND functional.

[FourT6and2]

Yeah, the tube sockets in an SLO layout are rotated slightly to accommodate the parallel runs of wire. This would require getting a un-drilled/tapped chassis and drilling your own mounting holes. Not worth the trouble for me.

But, I'm trying to find a way to wire everything up so it's super clean. I may copy a few wiring/layout methods from an SLO because it's probably one of the cleanest layouts I've ever seen. Well, that and a Mako.

Another option is to mod the circuit to run DC... Then running everything untwisted wouldn't be an issue.

[demonufo]

Another option is to mod the circuit to run DC... Then running everything untwisted wouldn't be an issue.

Really not worth the bother IMO. For decent results you need a seperate transformer, since you can't rectify 6.3AC down to full wave 6.3DC. And where would you put that to keep the layout clean and tidy? Just more mess to add to it.

Hiwatt style layout is the better (maybe even best) option, but it involves a complete layout re-design, and certainly isn't going to work with a standard Marshall-type chassis.

[FourT6and2]

How does Hiwatt do it? I'm having a hard time finding any decent pics. But from what I can tell it looks like they just route the wires to opposite sides of the sockets? So they're parallel, but further away from each other?

Or... not? I've no clue what's going on here: http://www.performing-musician.com/pm/j ... ternal.jpg" onclick="window.open(this.href);return false;

Looks very similar to Soldano's method. How is this different? http://www.tubetone.net/big%20photos/before.jpg" onclick="window.open(this.href);return false;

[Roe]

hiwatt twist the hearer wires. a slo isn't a quiet amp, so the lead dress may not be optimal

[FourT6and2]

hiwatt twist the hearer wires. a slo isn't a quiet amp, so the lead dress may not be optimal

Every SLO I've played has been noise-free, at least for a high-gain amp...

Are those photos I posted not Hiwatts? Because there are a lot of parallel lines.

[Roe]

I thought SLOs are known to be noisy? old/real hiwatts had twisted wires. the new stuff is quite different in many ways

[FourT6and2]

I thought SLOs are known to be noisy? old/real hiwatts had twisted wires. the new stuff is quite different in many ways

I've played 3 or 4 different SLO's and they've all been noise-free. Maybe a little hiss when the gain's turned up. But nothing out of the ordinary for a high-gain amp.

[demonufo]

hiwatt twist the hearer wires. a slo isn't a quiet amp, so the lead dress may not be optimal

+1.
Also, Hiwatt do twist the wires, but orient the sockets so it is neater and easier. But the whole amp layout just looks so pristine. At a quick glance I found this example, which looks like the amps that Harry Joyce's team built for Reeves (hiwatt).
http://www.tdpri.com/forum/amp-central- ... 100-a.html" onclick="window.open(this.href);return false;

[FourT6and2]

I found a good writeup on heater/filament lead dress here: http://www.freewebs.com/valvewizard/heater.html" onclick="window.open(this.href);return false;

An excerpt:

The lead dress of AC heater supplies is very important for noise reduction. The AC heater wires will have significant EM radiation and should therefore be routed well away from all signal wires, and are usually tucked into the corner of the chassis. The wires should either be made from twin cable (bell-wire) or better still, should be made by twisting the wires neatly and tightly together. In this way the wires are kept perfectly parallel and close to each other, which increases opposing field density and encourages the radiated fields to cancel out. Loosely twisted wires are no use at all.
When heaters are wired in parallel [as apposed to series], power valves should be first in the heater chain, followed by driver valves, with the input stage being last in the chain. This keeps current, and therefore radiated fields, at a minimum around the most sensitive stages of the amp. Even better is to run the pre-amp and power-amp sections from separate heater chains. If signal wires must cross the heater wires, they should do so at right angles.

The common pre-amp valves (ECC83 / 12AX7 etc.) when run from a 6.3V supply, should be wired from one side only, not by looping one heater wire all round the valve socket, which would create a hum loop and cause excessive interference noise (though many amp makers DO make this mistake and get away with it). The wire twisting must be kept very tight right up to the socket, where it matters most. Their pin arrangement is also deliberate, so that the main heater pins (4 and 5) can be orientated towards the chassis wall, allowing heater wires to be run along the wall away from any other sensitive signal wiring.

Now I understand why the Soldano SLO, Wizard Metal and some Mesas use straight bus wire instead of the typical twisted-pairs.