Attempted to do a quick bench test on my 65 radio. I used my 12 Volt battery charger. All I got was a loud humming noise with or without the antenna plugged in. Is the DC coming out of this charger too noisy for a bench test or should I pack her up and ship her out to the radio repairman? I did remove the faceplate to see the little black string which pulls the window for the AM/FM selector was off the wheel. Still the same unpleasant HUM. Who do you use to repair your radio's? Dick Gutman
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Re: Radio Bench Test
Often, the output of a battery charger isn't very 'clean' DC... Obviously, the way to tell is look at it with an oscilloscope, but most don't have one of these puppy dogs hanging around the garage. The majority of the chargers I've looked at with an o-scope deliver VERY 'lumpy' DC with voltage peaks rebounding at AC line frequency (50-60 Hz).
If you have to use a battery charger in place of a dedicated automotive grade bench supply, the best way to do so is to load it by connecting it to a real battery and then tapping the output of the battery to supply power to your test item.
You'll find a number of commercially available automotive power supplies for lab bench applications (eBay is pretty good source for used ones) that'll be rated at 13.8 VDC with current profiles in the 10-40A range. These are handy.
Another neat solution is to find a computer grade, uninterruptible power supply. Some of these have banana plug jacks on the back to let you 'daisy chain' additional DC batteries to extend the UPS unit's standby power output. If you use these taps as a source of power on the bench, you're essentially looking at the output of a motorcycle battery under trickle charge and it's a ROBUST automotive power source with a substantial reserve current profile! Used/rebuilt UPS supplies can be found on eBay for $20-40... -
Re: Radio Bench Test
Thanks Jack: I was trying to get a feel for the condition of this old radio before I sent it off for repair. I will try a battery next to see if that helps. At work we have power supplies up to 8VDC. Most of the power supplies we use are in the 100mv dc and below. We use to calibrate XY plots/ current sensors etc, of our Draglines DC machines. There are shunts in series with the armature circuits and we derive mv measurements from these shunts. Some of these DC armature currents are in the excess of 4000 amps DC. Coalmine chatter, sorry. Dick GutmanComment
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Re: Radio Bench Test
Hi Dick, just use a regular car battery and run a 12 gauge wire with a fuse on the positive side, then ground the radio to the negative side of the battery, and it's that easy.Comment
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Re: Radio Bench Test
Just use a set of jumpers and some small gauge wire and wire clips on the bench.
make sure you are using the correct speaker with the transformer, that might be your problem with the hum. I have tested mine with a 6 amp battery charger, and it worked.
Jerry FuccilloJerry Fuccillo
1967 327/300 Convertible since 1968Comment
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Re: Radio Bench Test
Hi Dick,
Following Jerry's recommendation as well as the those of the others, if your testing is less than satisfactory and you send your radio out for evaluation/repair, send it along with your speaker. The problem could be with the "transformer" (others refer to it as a choke or loading coil) on the speaker. It is considered a component of the radio, simply mounted externally for space and heat dispersion considerations, and many have gone out-of spec. I also understand that most of the reproduction speakers come with improperly rated coils that will cause the DS-501 transformers on the back of the radio to overheat after a short while, causing distortion, and eventual damage.
I have no experience with repairmen, so I can't personally endorse anyone, but Tony Mac Crutchfield (www.wonderbarman.com) and Carles Siegfried (www.nadjaart.com/charles/) do have a lot of useful information on their websites.
Best of luck,
LouisComment
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Re: Radio Bench Test
Dick,
I used a 12 volt battery to test my radio prior to installing it in my car and got the same results, just a hum. I was using an antenna. I was ready to send it out for repairs and called the person I had selected to do the repair and asked if he thought I had done enough investigating to determine the radio defective. He told me to make sure I had continuity through the antenna. The Corvette factory antenna has a capacitor built in some where and you won't see continuity with an ohm meter. How ever I was not using a factory antenna for my test so I was able to look for continuity and it was not there. I changed to another antenna that had continuity and the radio played fine.
Then I tried the radio in the car and it would not play. I had a brand new antenna but was using the old antenna lead in wire. Since it isn't possible to see continuity through the lead in cable I just bought a new one and gave it a try. It worked fine.
All I'm saying is check your antenna before you send the radio out.
I hope this helps, PhilComment
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Re: Radio Bench Test
the hum is caused by the charger. it is unfiltered. use your car battery and some long clip leads. i restore radios so if you need help let me know.
regards dickComment
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