First time on a modern spot, I felt guilty, like I was only doing half my job!
Where as the Troupers used an AC clock motor for carbon feed, the Supers used a DC motor, with the "field" coil actually being a loop of the carbon-feed cable. No arc, no feed, which was pretty cool if one was flipped on and not struck. (no self-stike/meltdown.) The drawback was, it was a brush type motor, so if the
commutator got dirty, you could end up with a dead spot and the motor wouldn't run. Easy to clean, but few knew about it! Also had motor speed wire-wound pot that would get dirty and have dead spots.
Hints:
1) First used in projectors for nefarious /cheapness reasons.
2) Engineers at Strong would have cringed!
Hello John;
In my mind, Troupers were AC arcs with matching carbons, both the exact same type, length and burn rate.
As you said, AC clock motors, constant speed, always ran the same direction, always pushing the rods towards each other.
Supers were DC arcs; front and rear carbons were different diameters, lengths, composition and burn / feed rates.
Front rods had hard centers, and soft perimeters so the perimeters would burn away easier and the centers would not become deep, shadowed craters.
The intensely bright end of the front rod was
the light source at the
reflector's
focal point, you were projecting a well focused
image of the business end of the front rod.
Rear rods had soft centers and hard perimeters so the center would burn away without extending into a long, thin, easily breakable
point.
Without the differing compositions (if they were both manufactured with identical compositions) the front rod's crater would get ever deeper while the rear rod's conical
point would grow ever longer. Were this allowed to continue, your intensely bright source would be deep within a cavern with the rear rod's
point way down inside and shadowing the source from reaching the
reflector. The difference in relative feed rates was accommodated by different thread pitches, threads per inch, on the common feed shaft driven by the DC motor as described in your post.
Whereas the AC Trouper's feed motor would operate when turned on, regardless of whether an arc was struck or not, the Super's DC motor would rotate the opposite direction upon turn-on, pulling the carbons apart, until an arc was struck when it would instantly reverse and begin pushing the rods together; one more reason for the spring loaded action required for igniting.
As to your comments on dirty spots on the speed adjustment and / or motor;
If your feed stopped, you only had so long to realize and correct before your arc was too long, blued and extinguished.
If your arc actually went out, the feed motor would begin happily pulling the rods even further apart.
Once you were a competent arc operator, keeping an eye on many things became second nature and life was easy.
Before you reached that plateau, every annoyance was rapidly a panic situation.
We’ve yet to get to the differences between silvered glass and polished metal reflectors nor have we touched upon drip shields and drip catchers within the
lamp house.
Sorry for blathering on, for those who ran arcs this is all 'old hat' but I suspect it's pretty bizarre info for those who've never shared the 'joy'.
As to the odd little gizzy pictured; I'd love to see three rods in the same photo; an AC, a negative and a positive to compare OD's to the diameter of gizzy's solid end. I was beginning to think it was some sort of extension to permit burning short stubs from the
butt pail but there’s no evidence of scorching / burning.
Geeeeze! I’m starting to write like Brian!!
Toodleoo!
Ron Hebbard
