Improving the Universal Shop Speaker and Dummy Field Coil

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Improving the Universal Shop Speaker and Dummy Field Coil

Post by Dale H. Cook on Wed Mar 09, 2016 8:52 pm

One of my favorite home-brew items of test equipment is my Universal Shop Speaker and Dummy Field Coil, which I developed for working on a chassis without needing the electrodynamic speaker, output transformer and field coil which are mounted in the cabinet:

http://plymouthcolony.net/starcity/radios/pages/unispkr.html

A project for this spring is to add a third cabinet to upgrade it to handle speakers with tapped field coils and dual field coils. The parts are all in house, I just need to set aside some time to build it. I would appreciate hearing from anyone who can document speaker plugs and cables not shown on my speaker plugs page:

http://plymouthcolony.net/starcity/radios/pages/spkrplug.html

Any information that you can provide on which makes and models use specific speaker plug wiring would be greatly appreciated, as most schematics for sets with speaker plugs don't show the plug wiring. That will also help me to revise and expand my settings page, which is abominably skimpy:

http://plymouthcolony.net/starcity/radios/pages/settings.html
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Re: Improving the Universal Shop Speaker and Dummy Field Coil

Post by Bill Cahill on Thu Mar 10, 2016 9:05 am

On some of their later sets, and, this includes TV's, RCA tended to have a jumper wire on the speaker end that connected the rest of the filters in the tv.
On 1950 TV's, RCA no longer used voice coils in most of their equipment. They had a standard 4 pin set up that disconnected the audio output tube if the speaker was unplugged so it would not have a melt down.
Their 1948 TV's had a four prong plug with two pins un used, and, the other going to the voice coil.

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