excess internal static in radio

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excess internal static in radio

Post by Sinatra1982 on Sat Oct 22, 2016 2:25 am

Replaced all caps and bad resistors. Get excessive internal static when trying to tune in stations. I can receive a couple of stations barely. Static is at low volume and high volume. Static bad when tuning low or high stations. Retired and just started working on radios. Also couldn't find good schematic. Nostalgiaair did not have it.

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Re: excess internal static in radio

Post by Wildcat445 on Sat Oct 22, 2016 2:34 am

First off, welcome to TRF! This is a good bunch here ready to help any way we can.

As to your radio, we really need more information on what you are working on....make, model. Is the volume of the static controlled by the volume control? A guess would be that the antenna is inadequate or something is wrong in the antenna circuit. Maybe someone else has a suggestion as well. Good luck.

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Re: excess internal static in radio

Post by Sinatra1982 on Sat Oct 22, 2016 2:42 am

Radio is a Philco Transitone Model PT-26. When volume is turned up the static is louder It one 4 foot antenna wire coming out thjrough the back of the chassis from the bottom inside of the chassis. All tubes light up but have not tested them on tube checker. Could a tube still be bad and light up? Not sure I know what you mean by he antenna circuit. Thanks.

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Re: excess internal static in radio

Post by Wildcat445 on Sat Oct 22, 2016 2:54 am

I don't have the schematic for your radio in front of me, but perhaps I can help some anyways.

Does your radio have a loop antenna on the back? If not, it uses a hank antenna, simply a length of wire. Typically, a four foot hank antenna is not sufficient unless you live somewhere with several strong local stations. A simple first step would be to attach a longer piece of wire to the antenna, maybe 20 feet or so if you have some. Most any type of wire will work for a test antenna. See if that makes any difference in the signal you receive, and if the noise is less or more. A tube can light and still not work. The antenna circuit consists of the components from the antenna itself, any antenna matching coil and part of the tuner in most radios. Good luck.

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Re: excess internal static in radio

Post by Sinatra1982 on Sat Oct 22, 2016 2:59 am

It does not have a loop antenna, just a 4 foot wire. There is a wax covered coil on top of the chassis next to the cap tuner. It has a paper cap going from one wire to the chassis. I can't get to it, so didn't replace that one. Could it be that cap?

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Re: excess internal static in radio

Post by Sinatra1982 on Sat Oct 22, 2016 3:00 am

I tried a lot longer wire to no avail.

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Re: excess internal static in radio

Post by Wildcat445 on Sat Oct 22, 2016 3:17 am

Have you checked for an external cause for the static? Lots of things we use nowadays can cause static in an AM radio. The possibilities are endless. You might move the radio to another room and see if that changes the static. You are almost to the point where you need to perform certain directed tests to chase down the exact cause of you trouble. For that, you will need a schematic. What type of test equipment do you have. VTVM? Tube tester? Signal tracer? Signal generator?

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Re: excess internal static in radio

Post by Sinatra1982 on Sat Oct 22, 2016 3:22 am

I have a VTVM, capacitor checker and tube tester. I can't find a good schematic for this radio. I have tried he radio away from any outside electrical interference, but no luck.

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Re: excess internal static in radio

Post by Wildcat445 on Sat Oct 22, 2016 3:59 am

You are really at a disadvantage without a schematic. Like baking cookies without a recipe.

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Re: excess internal static in radio

Post by 75X11 on Sat Oct 22, 2016 4:39 pm

Here is a good source for schematics.  They come on a DVD and you can print them out as you get new projects, or look at the schematic on one you are considering to see how difficult it is. 

http://www.ebay.com/itm/Vintage-Tube-Radio-and-Amplifier-Schematics-DVD-PDF-600dpi-/110319473326?hash=item19af8d92ae:g:VV4AAMXQwKdRfT6P
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Re: excess internal static in radio

Post by John Bartley on Sat Oct 22, 2016 4:49 pm

This may help for a schematic :

http://antiqueradios.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=155436

Does the static increase and decrease with the volume control? If so, the problem lies ahead of the control. If it doesn't, you may have a crystallized solder joint or a resistor breaking down in the audio circuit after the control. I had a steady static in an AA5 set one time that I traced to a screen resistor breaking down

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Re: excess internal static in radio

Post by Sinatra1982 on Sat Oct 22, 2016 7:40 pm

The static increases with the volume control, I can pick up a couple of stations faintly. When tuning the dial going up the scale it get louder.

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Re: excess internal static in radio

Post by Sinatra1982 on Sat Oct 22, 2016 8:08 pm

John thanks, got the schematic from your site. What does a crystalized solder joint look like? I soldered new caps and one resistor in the radio. Perhaps that is the problem. It got worse after I did those. I am not sure what it is called, but I believer it is a wax covered looking coil on top of the chassis next to the tuner cap. It has a small paper capacitor coming from one the connections on it and the other end is soldered to the chassis itself. I didn't replace or check that one because it is hard to get to. It is the only one I didn't change. Thanks.

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Re: excess internal static in radio

Post by 75X11 on Sat Oct 22, 2016 8:39 pm

A good solder joint should be clean and glossy on the surface like a water's surface.  Are you able to get a couple of pictures so we can see what you are describing?  That can help a lot.  A crystallized joint looks rough and often has points where the iron was lifted from it.  Liquid flux can keep that from happening.  It would be a good idea to go on and replace that last cap you mentioned that you hadn't replaced.
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Re: excess internal static in radio

Post by Sinatra1982 on Sun Oct 23, 2016 2:34 am

Just got the schematic for my Philco PT-26. My radio has a 4 foot single wire antenna, however the schematic shows it shows a loop antenna. Could that be why so much static and poor reception? Would any one know how the loop antenna is connected in the radio.
One end looks like it goes to the antenna IF transformer, but not sure where other end goes to, looks like maybe to a tube. Not good at reading schematics yet.

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Re: excess internal static in radio

Post by Wildcat445 on Sun Oct 23, 2016 2:51 am

One end of the loop antenna connects to the tuner, the other end connects to the AVC buss. The four foot wire is connected to an IF transformer, so that would probably be the AVC. Try connecting a piece of wire to the tuner and see if that helps reception. One part of the tuner would be the oscillator, so that one will not help performance. The oscillator part of the tuner should have a wire going to the converter tube, so maybe that will help you identify where to connect a dummy antenna. If this makes the radio play, you will either have to locate a suitable antenna or kluge something up that will work. Reception may not be great the way it is, alignment may help, but reception may not be optimal without the correct antenna. Good luck.

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Re: excess internal static in radio

Post by 75X11 on Sun Oct 23, 2016 9:35 am

What kind of static are you getting?  It is a white noise static?  Is it a rumble kind of like a thunderstorm.  Is it a 60 cycle hum, or a combination of two of them?  Did it change any when you tried the different length antennas?
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Re: excess internal static in radio

Post by Dan Walker on Sun Oct 23, 2016 11:09 am

http://philcoradio.com/phorum/
Try the Philco Phorum,, For the answers to your questions. Those guys know all about the Philco sets

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Re: excess internal static in radio

Post by Sinatra1982 on Mon Oct 24, 2016 2:13 am

It is a rumble kind like thunderstorm. Different length antennas didn't change anything. Which is the converter tube?
Can you tell me if it should be one antenna wire or a loop? The radio doesn't look like it ever had a loop, but the schematic shows is showing one. Could a bad resistor cause it? I only replaced one because the others or so hard to get to. Do you need to disconnect one end of the resistor to check he ohms? Sorry to ask so many questions but a how to book I am using isn't very clear to me and this is my first radio restore. I have replaced all caps.

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Re: excess internal static in radio

Post by 75X11 on Mon Oct 24, 2016 8:38 am

The reason I asked, is more likely as not the rumble is generated within the unit.  It could be anything from a failing resistor to a corroded trimmer capacitor.  It is best to check a resistor by removing one lead.  Do so in a manner that will stress it the least.  Someone has apparently removed the card mounted loop antenna from your radio. check where the wire is connected.  If it is at the end of the upper left dotted line in the schematic that is shown connected to the antenna at the left of the coil, that should be your external connection, but you have to get tho the bottom of this noise first.  Just take it a step at a time, and don't let frustration get to you.
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Re: excess internal static in radio

Post by Wildcat445 on Mon Oct 24, 2016 11:18 pm

I'm thinking that the noise and the lack of a matched antenna are all part of the same problem.

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Re: excess internal static in radio

Post by Bill Cahill on Tue Oct 25, 2016 10:23 pm

I agree with the post by John Bartley, and, add, It could be a dirty volume contro, dirty tube socket, corroded tube pins, etc. Of course, I Have seen many sets in my working carear that have a bad I F transformer. Some say, but, that wouldn't happen on a Zenith. In 1949 Zenith added the internal capacitors on the bottom of the I F transformer. Yes, I have found a number of those I F's to also be bad. What happens, with age, weather, and, depending on what kind of metal they used for the rivet, is the culprit.
As the metal rivet corrodes, it spreads corrosion to both the primary , and, the secondary coils. None are wired the same. I find them both ways. Good I F's, and, bad I F's.




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Re: excess internal static in radio

Post by chrisc on Thu Oct 27, 2016 6:40 pm

Hi - I was looking looking at a picture of one of these at radiomuseum.org (anyone can visit and see the pics ) - instead of the usual arrangement for the loop antenna at the back of the radio, it looks like is actually like a ribbon, run around the inside of the cabinet at the back. I rather think that you would need to duplicate that arrangement if yours is missing. It should be possible to make something that would work but you'd need to experiment to find close to the right number of turns

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Re: excess internal static in radio

Post by Sinatra1982 on Mon Oct 31, 2016 2:32 am

In doing some research for the proper antenna for this radio, I came across something that might account for my static problem, but I am just guessing. I saw where someone had a radio just like mine and he stated he had to put a non polarized power cord on it.
Mine has the original power cord where both pins are the same width instead of one wider and the other narrower. Could this possibly cause the excess static? Thanks.....

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Re: excess internal static in radio

Post by 75X11 on Mon Oct 31, 2016 9:07 am

It hasn't caused it in any of the radios I have restored.  As Bill said, the If's , or more likely their capacitors could cause such rumbling in your audio.  They are the mica capacitors connected to the IF transformers.  I got a pretty decent capacitor tester on ebay for not too much money that can help eliminate that as a possible cause.  Given the date your radio was produced, those caps would be outside the IF housing.
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