1956 wonder bar operation

[James S.]

After a long period of non use I started to run through a operations check, everything was great until I did the radio check !!!!! Radio plays and has a good strong signal but, the wonder bar when pushed continually scans and won't stop plus the pre-set buttons won't stop the scan working ???? Don't claim 2 B a radio tech, sure could use some expert advice .... Jim S.

[Jerry R.]

Re: 1956 wonder bar operation

Change the 12AU7 tube whose function it is to control the seek start/stop relay. Change the last 12AV6 tube while you're at it.

The push buttons may still be unreliable as the circuit board in the assembly, sliding conductive clips on the board (10 total) and another set of contacts in it are undoubtedly corroded beyond belief. That may or may not be a related problem.

Don't mess with the PB assembly unless you like taking chances. It's easy to clean up but easier to mess up.

Also, the PB control circuit as designed is not stable in the first place. It is best changed to a simpler design and approaches 100% reliability for very long periods of time when modified. (Just trivia info...)

There's a lot more that it could be but the 12AU7 and 12AV6 you can handle and not hurt anything. You said you have strong signals so it's probably not one of the other tubes. After that you're into changing wax caps and repairing 'IF' transformers...

Hope it's an easy fix!

[James S.]

Re: 1956 wonder bar operation

Change the 12AU7 tube whose function it is to control the seek start/stop relay. Change the last 12AV6 tube while you're at it.

The push buttons may still be unreliable as the circuit board in the assembly, sliding conductive clips on the board (10 total) and another set of contacts in it are undoubtedly corroded beyond belief. That may or may not be a related problem.

Don't mess with the PB assembly unless you like taking chances. It's easy to clean up but easier to mess up.

Also, the PB control circuit as designed is not stable in the first place. It is best changed to a simpler design and approaches 100% reliability for very long periods of time when modified. (Just trivia info...)

There's a lot more that it could be but the 12AU7 and 12AV6 you can handle and not hurt anything. You said you have strong signals so it's probably not one of the other tubes. After that you're into changing wax caps and repairing 'IF' transformers...

Hope it's an easy fix!

Hi Jerry !!!! Thanks for the quick response, I am planning on checking it out tommorow morning. I was just reviewing my 56-57 Corvette Radio service and shop manual and I see the 12AVU7 but no 12AV6 ???? there are 12BA6's.... Can you email me or give me a call 248-933-0946 Jim S.

[Jerry R.]

Re: 1956 wonder bar operation

I'd say that was the result of a senior moment but I'd rather give the credit to the inability of this PC to auto correct for my memory errors. Surely it just needs a memory upgrade.

12BF6.

Pins 5 and 6 are rectifier elements in that tube and often fail. The signal feeding the 12AU7 comes from that part of the circuit. The audio is pulled off the intermediate frequency (262KC) there also.

I'll drop a note via email Jim.

[Steve H.]

Re: 1956 wonder bar operation

James,
Let us know if it works as mine acts the same way.

Steve

[Jack H.]

Re: 1956 wonder bar operation

A few other tips...

(1) The radio has a sensitivity control to determine the received signal strength profile of a target station to stop on. Make sure you don't have a 'cockpit' issue here that thwarts the Wonderbar's signal stop function.

(2) These radios were NOT designed to withstand an 'infinite' seek situation. Don't let the radio scan the full dial more than a few times. You might be disappointed to see that puff of smoke from either the treadle or power solenoid going 'bye bye'...

[James S.]

Re: 1956 wonder bar operation

A few other tips...

(1) The radio has a sensitivity control to determine the received signal strength profile of a target station to stop on. Make sure you don't have a 'cockpit' issue here that thwarts the Wonderbar's signal stop function.

(2) These radios were NOT designed to withstand an 'infinite' seek situation. Don't let the radio scan the full dial more than a few times. You might be disappointed to see that puff of smoke from either the treadle or power solenoid going 'bye bye'...

Hey Jack thanks for the info, can U define cockpit issues???? I've tried tube swaps, antennia matching and printed circuit clean-up. Now trying to figure out next step!!!! Jim S.

[Jack H.]

Re: 1956 wonder bar operation

Hey Jack thanks for the info, can U define cockpit issues????

Cockpit issue = you've got the sensitivity switch set for a received signal strength level that's higher than the actual signal levels you're getting in your neck of the woods.

I've tried tube swaps, antennia matching and printed circuit clean-up. Now trying to figure out next step!!!!

You've covered the 'no brainer' issues. Now, it's time to take your copy of the Delco Radio manual's schematics, haul out your oscilloscope, and actually OBSERVE what's happening in the seek system's trigger circuit (12AU7)...