The AM Forum

This is a very long coil of heavy copper wire wound around a hollow fiberglass tube. Several series of triple tap loops are evenly spaced along the assembly.

If this was home-crafted then someone did very neat work.

Any thoughts? It looks unused...

I vote for a HB plate choke, tappable to work different bands.

73DG

At five and one half feet, regularly spaced but three tapped at only segment ends, quite the mystery. Possibly a short for freq. , vertical antenna loading coil.  Note the slats under the windings, probably superfluous as if someone was slavishly trying to match a published diameter but only had undersized tube stock, or for cooling, or for approx. air wound  "Q."

. At any rate the wire size can carry many amps, not ma. So must have been for a loooong and big glass bottle if it's plate choke.  ;D

Maybe it's a primary tapped winding for a Telsa-like coil. The secondary winding would be wound on a smaller diameter stock with much finer wire and fits inside the primary tube. Rather then moving the primary coil and securing it at various locations along the secondary coil, everything remains stationary. To vary the amount of secondary output, you make your various connections up or down at the tap points.

Or maybe it's a tapped coil for a big-rig mobile antenna tuner.

Looks like an inductor.


klc

I think it's a garage door spring,  probably another one somewhere,  usually you need two.   Most likely some sort of loading coil for an antenna.

That's the thinking that persuaded me to buy it. You know, one of those "I'll come up with a use for it on the way home" purchases. The XYL version is "I'll have to find a party to go to now that I have the perfect shoes".

The larger gauge wire will lend a wider response curve at the low SWR it was tuned for. Same deal with a dipole, driven element, ect. Or perhaps part of a still disguised as an antenna loading coil. Hi

Best
Doug
N5DMC

Hmm... did you measure the inductance?  I can think of one possibility - it _could_ be a PWM filter input inductor for a tube PWM.

I've would some, and there were tube PWM transmitters using large inductors as the input element to the filter.

Maybe not, but a possibility.  The inductance would be a strong indicator.

Using a signal generator and a series resonance test circuit, it measures around 140 to 150 uH end to end (frequency and capacitor accuracy dependent)

part of anode line for a distributed amplifier.

pulse forming network coil for radar or similar pulse modulator.

I think that coil is just part of a network where two are needed to feed ac to a tower lighting system. That would be the reason for so many taps. You would select the correct amount of inductance depending on the frequency that was being transmitted. When you found the least amount of RF at the ac feed point, you had the correct inductance. Towers for AM are above DC ground in case there are some out there who are not aware of this, except for monopole configurations. Maybe that was not the original purpose but it could be used that way.

One of the benefits of posting this kind of question is that it triggers all kinds of research not experienced since college daze.

I've got to go with the Pulse Forming Network answer for several reasons. First is the high length to diameter ratio for an inductor, allowing the large capacitors to be lined up along the coil. The second is the bunching of three taps at evenly spaced intervals, allowing the pulse duration to be adjusted.

(https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQJY20b2ulPJtBH6NBy6WdYxKqbkjXwhi2kliwSNkfz-ONOj1OdEA)(https://www.researchgate.net/publication/260708771/figure/download/fig4/AS:302064770011138@1449029261066/A-schematic-of-the-pulse-forming-network-used-to-generate-the-comparatively-long-lived.png)

That said, I still see it as a kick-butt antenna loading coil...

Sure looks like it but who can say?  Its geometry and appearance was familiar to me from hobby experience though I never messed with a radar powerful enough to require that large of a coil. It was some years ago but I still think it would be great to get some more hands-on that kind of gear. There is a great book on pulse forming networks and related topics. It's easy enough to read, yet detailed enough to experiment and design from. High-Power Electronics, March, 1989, by W. James Sarjeant (Author), R. E. Dollinger (Author)

... or it's a quadular magnetic paralysis-flux excursion controller for a potato launch system.

Really it's an audio delay line for echo phools.  Predates bucket brigade IC's by a half century.
Some listeners were way too picky about their phased arrival time golden ears, hence the tri-taps.
Best used with Western Electric theater amps. in small rooms.