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 Post subject: Chevy Truck Radio, lots of AC Noise???
PostPosted: Dec Thu 30, 2010 4:49 am 
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Location: Sandwich, IL, USA
I just finished a 986771, 1954 Chevy Truck radio. Re-capped it all, re-stuffed the filter, tested all the tubes, installed a SS vibrator and 1600v cap. Tried it in the basement, then upstairs in the garage and there is a lot of what seems like AC noise in between stations and when I have a weak station tuned in. I don’t notice it much when I’m tuned to the strong stations. When I grab the antenna with my hand the volume drops quite a bit but the noise almost disappears.
I turned off the 4’ fluorescents and the compact fluorescents, that didn’t help.
Any ideas??

Denny Graham
Sandwich, IL


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PostPosted: Dec Thu 30, 2010 5:07 am 
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Sometimes they are a lot quieter when installed in the vehicle than when operated on the bench. I believe this has a lot to do with the massive amount of metal surrounding the radio acting as a ground plane against the antenna. You also have to use a battery to power the radio when doing final testing, almost any type of power line operated battery eliminator only makes the noise situation worse.

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PostPosted: Dec Thu 30, 2010 5:32 am 
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Tks Dennis, the vehicle is in Albany, New York and I'm 60mi. west of Chicago so that taint gonna happen till I ship it back to the guy in a few weeks. I don't have a bench power supply, my HP power supplly crapped out on me and they wanted hundreds to just open it up so I scraped it. Now I just use a 6v battery out of one of my Trucks. I've got the antenna mounted on the edge of an 8'x3' metal shop table, don't know if that would count as a ground plane. Never did understand that ground plane thing.
Denny Graham
Sandwich, IL


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 Post subject:
PostPosted: Dec Thu 30, 2010 5:48 am 
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I would expect that substantial metal bench to be a decent ground if the radio and antenna base were both connected to it.

Where's Meade? Let's get his input on this one.

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Dennis

Experience is what you gain when the results aren't what you were expecting.


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 Post subject:
PostPosted: Dec Thu 30, 2010 1:18 pm 
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I will assume this is being powered by a battery.

If the noise & Hum dissapears with no antenna connected (assuming it only has the normal plug in car type). Then the noise is external and there will be precious little, that you can do to be rid of that.

Marc


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PostPosted: Dec Thu 30, 2010 2:12 pm 
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It seems my shop is the worst when it comes to AM car radio interference. Yet a Philco 60, sitting a couple feet from the bench, works just fine. I just attribute it to a lot of interference from bench test equipment, not to mention the poser supply. As was just mentioned, does the noise drop or disappear when you remove the antenna? If so it's in the air, and the radio is only doing its job.

The one and only thing INSIDE the radio that can cause this is the vibrator power supply. These are always noisy, and of course there are filter and buffer caps, and this section is generally shielded off from the rest of the radio -- sometimes even on a separate chassis.

However generally when I hear a lot of noise and am suspicious, it's usually before I even GET to the power supply. With vibrator and rectifier removed I connect 230 volts from a bench supply -- and hear the noise. I've gotten so used to it, I can tell whether or not the radio's normal. Sometimes a bettery or isolation transformer to the power supply will help, sometimes not.

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 Post subject:
PostPosted: Dec Thu 30, 2010 5:07 pm 
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There was a faulty grounded piece of eqpt in my shop and everytime a car radio was fired up there was so much noise wasn't able to get any stations.

Even had the local utility company come down and they replaced boots and connectors at the feeder,

Then one day the source was disconnected and all the restored car am radios started playing fine. Some external source could be causing the problem as you already know.

Good luck.

billn


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 Post subject:
PostPosted: Dec Thu 30, 2010 5:34 pm 
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startinagin wrote:
There was a faulty grounded piece of eqpt in my shop and everytime a car radio was fired up there was so much noise wasn't able to get any stations.

Even had the local utility company come down and they replaced boots and connectors at the feeder,

Then one day the source was disconnected and all the restored car am radios started playing fine. Some external source could be causing the problem as you already know.

Good luck.

billn


I've had things like that in the past. Some strange noise, affects anything in the room. Unplug pieces of test equipment one at a time, suddenly goes away. Nowadays I live with it. Again, I'm so used to it I can tell if the radio is acting up or it's normal.

In this particular case, the radio was on a battery, and it was moved to another room. Good troubleshooting, but still did not provide a conclusive answer.If it were me, I'd try disconnecting the antenna. If noise quiets down along with the reception, that's proof it's picking up the noise from the air. Only other thing to check is alignment -- which can help increase signal over noise, but if everything on the radio checks out, it should be fine. BTW, did you check the antenna trimmer? Be sure to give instructions for adjusting this in the truck. Once installed, reception should be sharp -- probably so much better in the truck that he won't notice the noise even if it DOES follow the radio there, which it most likely won't.

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 Post subject:
PostPosted: Dec Thu 30, 2010 6:12 pm 
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Bench and cabinet were connected, however, it makes no difference when they are, I ran a strap between the two and it dint change a thing.
Yes Marc, 6v battery powered. I’m not the best at trouble shooting so I didn’t make the connection in my mind with the input till you mentioned it. Nope, no noise when the antenna is disconnected, just a very, very slight background noise I suspect from the vibrator. Does a SS vibrator still generate some back ground noise??? Like I said Gary, it’s battery powered. Has to be something generating the noise in or around the house.
Man, I’ve turned off about everything in the house or within 50 feet of the radio and none of it helped. Actually I didn’t try this before but my digital JVC tuner gets the same sort of noise at low power stations and I can even hear it a little in the back ground on the strong stations so it is being broadcast from something local.
Yep Gary, I adjusted the trimmer, but just for the antenna setup I have at the bench, not actually in the truck. I’m bout 99% sure now that it’s external.
Maybe the best test would be to load the radio, the battery and the antenna into the car and drive out into the country to give it a test. Then, maybe I can feel confident enough to box this thing up and send it off to Albany.
Believe it or not, I’ve got over 75 hours of bench time on this piece of scrap that should have been sold for the few parts that were still usable. And many more chasing down parts, de-rusting in the phosphoric acid tank and driving to pick stuff up that aren‘t logged. I’ve sunk about $200 in parts with the plating and all. New speaker, dust shield, vibrator, caps, tubes, cad and chrome. I’m really gonna take the pipe on this one for sure. This came with four other radios that were pretty much junk also that I was supposed to get a radio for myself out of and an electric wiper motor. Both the ‘54 radios and electric wiper accessories are fairly rare birds so I didn’t want to take the chance of missing them.
I almost turned down the deal, but the challenge was there and then once I got into it, I couldn’t back out of it. Well this nightmare is almost over, then I can look forward to attempting to piece one together for my own ‘54 truck from the left over parts.
Thanks for the comments, have a good new year.

Hey Gary, sent you a PM

Denny Graham
Sandwich, IL


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 Post subject:
PostPosted: Dec Thu 30, 2010 6:43 pm 
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Location: Detroit, MI USA
Denny Graham wrote:
B
Maybe the best test would be to load the radio, the battery and the antenna into the car and drive out into the country to give it a test. Then, maybe I can feel confident enough to box this thing up and send it off to Albany.


I really like that idea. Should give you a definitive answer.

In my experience, Solid State vibrator replacements can create every bit as much background noise as mechanical ones, sometimes maybe more, because they can have very sharp on-off switching. I have built a fair number of FET based replacements for those who insisted on a modern solid state device but don't see any real benefit considering the limited use these old radios will get.

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Experience is what you gain when the results aren't what you were expecting.


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 Post subject:
PostPosted: Dec Thu 30, 2010 8:48 pm 
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The SS vibrators in the car radios are almost a necessity now days in most cases Dennis. The original mechanical vibrators are next to impossible to find. I wasn't smart enough to figure out how to repair a radio when I was a teenager in the 50's so I either did without or had someone who knew his stuff fix it for me, mostly did without though. I've read that even back in the day when you could run into any Western Tire store or local Radio & TV repair shop and pick up a vibrator they were only good for about a year. I’ve taken several apart and cleaned the contacts and re-adjusted them on my tube tester and they work good. In fact I‘ve got one I rebuilt in the stock AM radios in my 1950 Chevy truck. But like you say, those radios don’t see that much use now days. Heck, I’ve been trying to get my girl friend (that would be my “big old wife”) out on a date and then go park with me on some lonely road and listen to the radio all night for years, but I tain’t had no luck lately. Bout the only use the radio gets now is when me and the dog go for a ride in the country a couple of times a week.
Denny Graham
Sandwich, IL


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 Post subject:
PostPosted: Dec Thu 30, 2010 10:52 pm 
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That radio might be a piece of crap, but believe me it's got some value. Lots of trucks being restored, small percentage have radios. The radios that ARE out there look like they've been through the mud with the rest of the truck for 50 years. So a nice clean example is worth its weight in gold.

About the only saving factor, that's kept the value out of the stratosphere, is the fact that reproduction radios are available -- new stereos that look original. But if someone wants a 100-point vehicle, he'll pay big bucks for a good original AM radio for this truck. And actually, this radio is NOT really a piece of crap, aside from the torture it has taken over the years. It's not a bad performer. No pushbuttons, I think these were done away with due to the rust/dirt factor of the truck. These trucks had manual radios right on through the mid 1960's.

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 Post subject:
PostPosted: Dec Thu 30, 2010 11:03 pm 
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Denny: I have nothing to offer on your noise problem, but I'm curious: how do you test and adjust a vibrator on your tube tester?


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 Post subject:
PostPosted: Dec Fri 31, 2010 3:41 am 
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Location: Sandwich, IL, USA
By using an adaptor made by Sencore back in the day Alfred. A couple of lights on top of the unit both trigger when it is adjusted properly and balanced:
http://www.pbase.com/dennygraham/image/131505527/large

So, what do you think this restoration is worth Gary??
http://www.pbase.com/dennygraham/image/131505524/large
What you said is just why I took this project on to begin with. Hard to find these as this model truck because it was only made for a little over a year and the radios are specific to the ‘54-’55 1st series trucks.
This was the starter:
http://www.pbase.com/dennygraham/image/131506082/large
http://www.pbase.com/dennygraham/image/131506085/large
http://www.pbase.com/dennygraham/image/131506101/large
Denny Graham
Sandwich, IL


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 Post subject:
PostPosted: Dec Fri 31, 2010 4:07 am 
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Is it possible that it could be caused by a bad connection, a cold solder joint on a bypass capacitor or some shielding? Have you tried substituting tubes? Nice work on the metal box by the way, actually what you started with didn't look too bad other then the speaker, I've seen some car radios that looked like they were salvaged from a bog.
Best Regards
Arran


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 Post subject:
PostPosted: Dec Fri 31, 2010 5:04 am 
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The solid state vibrator still puts out a fairly good square wave, which as has been pointed out, is equally as savage as the points of the mechanical type.

The battery does make a good filter however I have seen 200uF on the battery side of some vibrator sets. The "Spark" plate in some radio's, is actually a large capacitor.

Do not be tempted to up the value of the filters on the B+ as that can cause hassles with stripping the cathode, with a valve rectifier.

I would think with the noise of the truck a small amount of square wave noise may only be noticed when it's stopped.

Just make sure all the earths are good along with any shields.

Marc


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 Post subject:
PostPosted: Dec Fri 31, 2010 8:34 am 
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Marcc wrote:

If the noise & Hum dissapears with no antenna connected (assuming it only has the normal plug in car type). Then the noise is external and there will be precious little, that you can do to be rid of that.

Marc




Here's another possibility: Maybe the noise is picked up externally, but is caused by something internal----If the test antenna is close to the radio, and the radio's covers are off (especially the little square metal cover over the power supply section in this model radio), the antenna could be picking up noise from the radio's vibrator power supply. In this case, unplugging the antenna would stop the noise.

Sorry I got in on this one late; I've been off trying to find a control shaft for Gary's 49 Cadillac radio. No luck yet, Gary. :cry:

I've had solid state vibrators cause a high pitched whine in the audio in some radios. Experimenting with an electrolytic capacitor on the incoming power section usually cures it. Something on the order of 220 to 470mfd at 16 volts worked for me; sometimes before the line choke, sometimes after the choke. Observe polarity of course.

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 Post subject:
PostPosted: Dec Fri 31, 2010 1:51 pm 
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Well Arran, thank the Lordy we don’t have any Bogs around here, or sure as heck some would be digging thru one and surely I’d be the one that ended up trying to what ever they dragged out of it. If you’ve salvaged radios that looked worse than that then you’ve go a lot more moxey than I have, that’s the worst one that I’ve had to work on in 20 years. Of course this is just a hobby and I don’t restore all that many radios.

Marcc, the filter can was a pair of 20uf @ 400v and I re-stuffed it with 22uf @ 450v, that shouldn’t be a problem should it? In these old trucks in order to hear anything you have to have the volume up half way. Just didn’t know if the SS vibrator would generate much noise but it sounds like I can expect some. Only shield is a tin over the vibrator circuit under the chassis., its in place, down tight and well grounded to the chassis. I went to the trouble of stripping anything that would come loose and having it Cad plated just so I wouldn’t have a grounding problem, I’m not a big fan of paint on radio chassis. Some times it’s the only solution. I did have to resort to using a little paint after wire brushing the outside of the chassis on this radio which can be seen as the center ring in the pictures. With every thing that is riveted to the chassis I’ve yet to find a practical way of fixing a rusty chassis. I did check ground continuity of riveted components, I’ve had problem with rusty rivets loosing contact before.

Thanks for chiming in Meade. No the radio is complete now, surrounded totally by its metal shell. I know what you mean about those controls. The VOL & TONE were fine on this one but the ON/OFF switch at the bottom of the stack was intermittent. Can’t find the CTS WH switches any where so I’ve had to go in and fix them like I did on this one. Some pixs of the fix: http://www.pbase.com/dennygraham/986771_radio&page=all
I had a Philco radio/record player up on the bench last year which had the phenolic board in the volume control broken into 5 pieces, I managed to fit it back together and re-glue some thin stiffeners under the cracks. It worked out great and is still working fine. Tried Mark Opatt over the years but I never seem to get any response from him. The problem with repairing controls, especially ones that are a triple stack like this is the time involved. I can spend a whole day just rebuilding one. There have been times I’ve have had to make new support posts on the lathe and tooling to re-rivet them back together.
Got no high pitched whine on this one, thank god! As I mentioned earlier, I’m getting the same noise at the other end of the house on a JVC boom box and it’s a tunable noise with the volume and its gone with the antenna unplugged so I’m sure its external now.

Once again, thanks a bunch for the input guys and have a prosperous new year. What did we ever do with out the internet!!!!

Denny Graham
Sandwich, IL


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 Post subject:
PostPosted: Dec Fri 31, 2010 2:31 pm 
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Hi to all. I've had this problem a few times. Most often it's in the 2-chassis MoPar sets in the 1949-54 era. I had one especially stubborn 1954 Chrysler radio for noise that I worked on 3 or 4 times. Power supply or 6 volt battery, didn't matter. In fact the owner packed it poorly one time, the volume control took a BAD hit and I had to get a parts radio to fix it. The "umbilical" cord between chassis had been repaired twice before I got to it and was so bad I made up a new one. I went over every connection-all were good. The electrolytic can was not restuffed on this radio-it was rewired so all the caps were under the chassis. I tried all sorts of tricks with lead dress-nothing seems to help. In desperation I tried some high-value electrolytics along the 6 volt input. A 220 uF /16 volt cap dramatically reduced the noise. I made sure the owner was going to keep the car positive ground so I put cap in the right way. Radio happily never came back.

I repaired a similar '54 Chevy truck radio about a year ago. It is a rare bird. I was fortunate that the one I did was easy-just needed new caps and a vibator. It took several phone calls to get the owner to hook the speaker up corectly.

I have only had SS vibrators a few times. I note the noise they make seems more like a whine as opposed the buzz from mechanical vibrators. I still repair my stash of mechanical vibrators. A few % of them work OK as found. I usually open them up and rework them. With my luck, I'll get a call/email 6 moths down the road saying, "the radio quit" if I don't make sure the vibrator is trustworthy.

I've had a handful of volume control sad stories in 2010, the bulk of them from being p+++ poor packing. Several ARF-ers have been of great help to me in that department. I've had some practice as well with my Dremel tool cutting shafts and making "split ends".

A blessed 2011 to all of you.

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Yes, it plays. No, there was no FM stereo in 1932. Yes, some people still enjoy AM radio.


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 Post subject:
PostPosted: Dec Fri 31, 2010 3:26 pm 
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I rarely bother re stuffing cans, however, the main thing is to make sure that there is little scope for the positive of one, shorting to the neg. of the other (non conductive wad), or the positives shorting too the can. In some cases I have lined cans with a bit of elephant hide (insulation paper).

Do beware that I have found Silicone compounds that are conductive

Marc


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