Crawls Backward (When Alarmed)

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Tube Filament Wiring, Part 1

While you weren't looking, I mounted the power transformer, choke and output transformer to the chassis.  It now weights a ton and since the PT is at one end, it's also unbalanced.  Not that any of that matters, but I just thought I'd throw it out there.

So, lookit all dem wires!  Geez, what the heck? 

It's actually not too bad - the reds are the B+ (high voltage) line, the yellow is the rectifier filament (5v) and the green is the filament line.  Ve chust poot dem to de right place, ja?  Hopefully.

I have to make a set of twisted pairs for the filament wiring.  So I just chuck them in my English 'egg-beater' drill on one end, and in a vise on the other.  Then I turn them and voila! you have a tightly twisted pair.

Coupla things.   This time I procured some solid core 20 gauge wiring to do this.  This stuff is real hard to turn, so I wound up using an electric drill rather than the hand one.  It went ok, I just used a real slow speed.

Second, I don't think I'll be using cloth-covered wiring for filaments anymore.  In twisting it, the outer cloth layer tore a tiny bit in a few places.  The inner (white) insulation is fine, but the little tears don't look great - if anyone would ever get six inches away from it and look.  So I think I'll use modern wire the next go-round.

On the other hand, it does look very cool, and of course, vintage-appropriate.  If you look at the bigger version of this image, you can see the fuzz on the cloth.

Why do we twist the filament wiring, you ask?  It's because the filament line is AC (6.3 volts in this case), and AC voltage will produce hum in the amp's output if it's close to signal wiring.  Early telephone and radio engineers figured out early on that twisting the filaments in this way concentrates the AC field around the wires.  If the filament line is kept away from signal wiring, it will be much less liable to introduce hum. 

The rectifier is wired up and I'll get the other wiring going too.  I need 2 days to bring the amp up on the variac, so I'm hoping to have it done by the weekend when I can fire it up.


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