Heater lead dress

[C Moore]

Why does everybody have hardly any twist in the heater wires of their Express builds???
I am not a very experienced builder, so pardon me for asking, but my Express has tight heater lead dress just like all other amps.

[M Fowler]

Ken F. designed the Express with what has been called the lazy loop filament wiring style. For a traditional TW amp it's required

If your building along the lines of less traditional adding other things or redesigning then you may want to go with tightly twisted filament wiring, DC wiring etc. Its up to you.

Mark

[C Moore]

So what was Mr. Fischer onto? When he was working the Express chassis, did he have some problem that he fixed by opening the loops of the heater wires? You wouldn't start a new design like that.....would you?
Thanks

[crbowman]

Somebody correct me if I'm wrong on this...........
I think Ken took some inspiration (certainly in regards to the Express) from the earlier Marshall amps which also had this kind of lazy loop flat against the chassis heater layout although Marshall did dress the heater wiring closer to the rear wall.

[PlinytheWelder]

It works fine just as long as you keep the other wires at 90 degrees and raised and all the other stuff that goes for good lead dress.

FWIW on mine, I put each preamp tube heater out of phase with the next one... It seems to work.

[RJ Guitars]

Lazy or tight, if the two stay close enough to each other it's good enough.

I figure Ken just didn't get the joy out putting two pieces of wire into his electric drill and making a tight twist. This activity happens to be one of my personal favorites.

rj

[gearhead]

I figure Ken just didn't get the joy out putting two pieces of wire into his electric drill and making a tight twist. This activity happens to be one of my personal favorites.
rj

Me too! Thought I was alone in this affection.

[Noel Grassy]

^+1

Does everyone wind theirs in reverse?

[Structo]

No, does that help keep the electrons suspended?

[rbryerton]

No, does that help keep the electrons suspended?

It depends on which hemisphere you're in.

[rp]

I figure Ken just didn't get the joy out putting two pieces of wire into his electric drill and making a tight twist. This activity happens to be one of my personal favorites. rj

gearhead
Me too! Thought I was alone in this affection.

You know, you guys can get jobs as alarm / security installers and do this half the day.
javascript:emoticon(':lol:')
My fave part too BTW

[Cliff Schecht]

There is another reason why Ken could get away with his lazy loop method. Look at how he has the decoupling setup on each stage. The first two stages are connected to the same B+, whereas the lone third stage gets it's own RC decoupling network. With the first two stages, each stage is inverting so any hum induced in the first stage tends to get canceled out by the second inverting stage. So the B+ there (B5 in the schematic) stays relatively clean by the self-canceling action of the two inverting stages. Since the third stage (the B4 stage) is all alone, it gets its own RC decoupling to keep noise in that stage down. The last two push-pull circuits have their own inherent noise cancellation but also get decoupled to keep noise low.

The lazy loop method works if you are clever about how you manage noise in the design and layout phases. The spots where signals do have to cross heaters are at 90 degree angles and are at least somewhat physically isolated. This is the tried and true method for keeping heater noise down in any tube amp (minus DC elevated heaters).

[RJ Guitars]

Cliff,

It's always great to have the engineering perspective, nice work in sorting that out!

It occurred to me after I made my first comments on this topic that one other thing can be done with the lazy loop. I think of the tube heater circuits on each tube as having a polarity, meaning you want to connect the center tap of each heater, on each preamp tube to the same wire.

I've found that I can run a single wire from the source to each tube, then add the 2nd wire after the fact. With a lazy loop this is possible and it allows you to use the same color wire (like all red) and never get them confused. I know this isn't a big deal but just a little something you can add to your bag of tricks.

rj