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What are the green and black wires out of the top of an AM (assuming 1958)wonderbar for? Are they the speaker wires? Also the speaker is non original (it is not even hooked up) I noticed that original speakers came with a small transformer like device near the speaker connections on the back of the speaker. I guess this is to match impedence w/ the radio?? Can I hook up the wonderbar to a modern speaker (assuming ~4-8 ohms) without damaging the radio. I just want to see if the radio even works. It lights up but it doesn't "seek" stations. Any info on wiring regarding this matter is appreciated. Thanks, Ken
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Re: 58 wonderbar
Hum, must be the 10th time this year I've given this 'pitch'.... We do have archives!
The early Corvette radios used a DS-501, germanium, speaker drive transistor. It had limitations in terms of dymanic response, but WAS a break-through implementation of AT&T's new patent (TRANSISTOR). This saved radio designers a LOT of real estate and cost (compare your WB set to an earlier unit from, say, 1956 with its HUGE speaker/power supply enclosure).
The drawback was one of audio band frequency response dynamic range or 'acoustic coloring'. To solve the problem a matching transformer was installed on the speaker (typical Chevy passenger cars had more room behind the dash and the matching xformer could be moved into or mounted on the backside of the radio chassis).
Without this matching xformer between the radio's xsistor speaker drive and the speaker itself, two 'funnies' happen:
(1) The acoustic 'quality' will be terribly different.
(2) If you drive a conventional speaker very long OR at high volume, you'll BLOW the DS-501 output xsistor.
Since there are FEW modern day semiconductor houses dealing in 'archane' germanium transistor fabrication, you'll be out a minimum of $25 to replace the blown xsister (Wow!) plus technician bench fees if you didn't go to college and get an EE degree or become an electrical tech....
This is WHY you can find Corvette radios on eBay and in swap meets that 'look good' but don't work when you get home. Prior Corvette owners decided to 'upgrade' their radio by installing a 'best money could buy' speaker and got shoddy sound quality AND shortly thereafter, found the radio quit altogether (square peg in round hole--mis-match between radio chassis and speaker).
Now, a competent repair tech, knowledgable in the art, knows he CAN run the set with a conventional 4-16 ohm speaker on the bench IF:
(1) He keeps the volume down.
(2) He doesn't exercise the set long (minutes NOT hours).
(3) He understands the sound quality will be poor/tinny.
So, the answer is a qualified 'yes'. You can run your WB on the bench with a conventional speaker IF you understand the three caveats listed above.... Also, if you want to 'soup up' your audio, you CAN buy the latest/greatest high efficiency/acoustically flat response speaker and install it IF you put the matching transformer in series with it.
Once the effect of the germanium xsistor and the speaker matching xformer was understood by designer, they took advantage of the presence of the matching xformer. It represented an acoustic response filer 'pole'. So, why not use the existing/required 'pole' in the overall frequency response of the system?
Funny--other Chevy radios improved with after-market add-in speakers EXCEPT Corvette that deteriorated.... Why? The matching xformer was IN the radio on Chevy cars and ON the speaker in Corvette.
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Other questions you ask (what is green/black wire?), get a support library with wiring diagrams to support your investment in classic Corvette. This literature is available (for a fee) and all is explained/described. But, basically, yes, grn/blk was the color code convention for an acoustic/spkr interconnect harness in those days. But, exiting the 'top' of your radio chassis seems incorrect (the only wiring on TOP was the dial indicator lamp power lead)....
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On bench power hook-up, the AC-Delco service manual will explain there are two separate power inputs to your radio set (along with complete circuit schematics). One power input supplies the chassis main power lead. Another terminal is chassis ground. The third terminal is instrument panel, dial illumination. So, without having a 'roadmap', you can get two of the three lead right and wind up simply power the dial lamp indicator bulb....
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