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In Reply to: RE: What am I? posted by Lee of Omaha on July 13, 2016 at 15:50:44
Hi
The field coil was often part of the power supply being a choke(inductor) between the rectifier or capacitors. Most tube amplifiers of that day had several power supply voltages, each was often taken from the highest voltage and stepped down via resistors.
The way that one is wired, it is my guess that there are two field windings and each serves different voltages (and the DC current producing the magnetic field).
Sometimes the resistance of a choke took the place of a resistor and so it may have been serving double duty.
The clever thing about this was that the residual hum in the power supply produced a hum in the speakers magnetic field which (when everything was right) canceled out the power supply hum in the voice coil drive (in this speaker the VC is the two wires that go off to the left side into a hole in the frame).
Looks like a very beefy driver if that is in scale and a 15"
Best,
Tom
Danley Sound Labs
Follow Ups:
So, from left to right, it looks like
- voice coil
- common
- field winding 1
- field winding 2
?
Hi Lee
I can't see all the details in that picture 1 but it looks to me like the thin grey and yellow wires to the left, which pass through the frame are the VC connections.
Normally these would not be connected to the field winding but I can't see from the picture with certainty that they are not tied to it at the terminal strip.
There appears to be a heavy red and black wire coming out of the right side of the field winding and I can't tell exactly where those go. Can you inspect this in more detail?
Starting at the left as terminal 1, it goes to the yellow VC wire, terminal #2 appears to be connected to the black VC wire.
I can't see if the black and red field wires also connect to that or what they do. As the output transformer VC winding is floating, to save wire, it could be common to the field but that would be unusual.
Terminal #3 is the black field wire and #4 the yellow field wire.
Can you give the black / red field wires a closer look and conform what they do?
Can you also lay a ruler across that "U" magnetic return and give me an idea how wide that is (for my own curiosity) and let me know what that speaker is out of.
Best,
Tom Danley
I don't know what it's out of--I just got the speaker. The magnet return is just short of 5 inches long.
I measured the resistance across the various terminals.
Terminal 2 is common to all three windings. The heaviest wire measures a little over 1 ohm, the other (probable) field coil measures about 12 ohms, and the voice coil winding measures a little over 14 ohms, making it probably a 16 ohm speaker.
One member responded that it looks exactly like the speaker out of his jukebox. Anyone know who made those?
Hi Lee
Well i wouldn't be surprised if it was from a jute box or large console radio. Seeburg was in Chicago as were a number of loudspeaker mfr's.
There was;
Oxford loudspeakers
Cynaudigraph loudspeakers
Jensen Loudspeakers
Heppner loudspeaker (northern suburbs)
And i am sure i have forgotten a few Chicago companies
Also parts mfr's like Alpha products, Nu way and others.
I have to say the twin field coil winding is not as common as 1 winding and based on the basket design, it looks like an American driver, perhaps an RCA or Magnevox.
Here are some sample pictures;
http://www.canuckaudiomart.com/details/648998808-magnavox_15_field_coil_woofer_1950s/images/442367/
https://www.google.com/search?q=large+field+coil+woofer&source=lnms&tbm=isch&sa=X&ved=0ahUKEwic66jkkfjNAhWIlx4KHWNhB1QQ_AUICSgC&biw=1607&bih=919#imgrc=L9PghkaO-hdyzM%3A
http://edsgoodstuff.com/edscart/bmz_cache/5/538b18bf4e29a1a6c6811c39f9f2dbb4.image.600x450.jpg
http://thumbs.ebaystatic.com/images/g/p8AAAOSwmtJXbAX4/s-l225.jpg
I couldn't see the back cover but Jensen used a cap over many of it's drivers even after going to permanent magnets.
Hope that helps
Tom Danley
Danley Sound Labs
Thanks so much for the links to photos. It looks most like the Jensen. The basket style looks the same, as does the style of the numbers.
Yeah that's a good bet i think!.
Looks like a nice driver with a magnet return that large.
When I had my Seeburg speaker reconed back in 1981, the tech said it was a Jensen.
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