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3 Feet of Superhet

6/2/2015

1 Comment

 
A new addition to the museum graciously donated unrestored from the estate of Mel Sylvia K6CRW.

OAKLAND AUTOMOTIVE SPECIALTY CO.        INVINCIBLE
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Research on this 10 tube superheterodyne leads to the manyfacture of the transformers, Madison Moore, of which it has the set of 5, numbered 1 through 5. Other leads to the Oakland auto manufacture, which became a part of GM seem to be a dead end. It is almost certain that this radio was sold around 1925 or 1926 as a kit. There are examples of an 8 tube variation for which the schematic is listed in the Riders manuals.

Underside view showing the chrome cased Madison Moore transformers.
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This radio differs from the 8 tube version most significantly by the use of push-pull UX 171 output tubes which incorporate a center tapped plate choke with the center tap going to the high impedance speaker.

The first audio transformer has a secondary winding that measures 27K ohms. That must be a LOT of wire. Fortunately it is intact.
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An interesting note: All of the capicitors have the values either scrapped (paper) or ground (Bakelite) off of the labels.

Video of operation. Touching controls, once tuned, is- well- it gives you something to do.
At just under 3 feet long, it take up a lot of shelf space.
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The only modifications, following the original construction, seem to be the addition of a second headphone jack (interior) and combining the dial indicator lamp switch function from two switches into one. The second switch is still there but has no function.

A very nice addition to the display.
1 Comment
Wilson Lamb
11/11/2022 08:16:38 am

Hi Russ,
I just posted on the forum for info on an Invincible, cabinet style, on legs. Then I found yours, which is entirely different. Radiomuseum has data on one from Australia, but no picture. Do you know anything about the cabinet model?

In your video, there is a heterodyne squeal on both sides of the station. My first super, a Lacault, does the same thing. Can they be cured? So far, I don't have a workable theory about what's happening. Could the LO signal be so dirty that there are spurs that beat with the signals? Would reducing the LO amplitude help?
Wilson
NC

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CUSTOM DESIGN BY SUE WEBB  06/2013       Redesigned by Russ Webb     Approved by Fuzzy   Updated:  Pretty much all the time, but I forget to change this date
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Photos used under Creative Commons from valart2008, rafeejewell