Help!!!

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Help!!!

Post by frank1956 on Thu Jun 19, 2014 2:23 pm

Hi everyone,
I need some help bad. I just got through replacing all the capacitors and Electrolytic in my Silvertone 3004 Chassis Ch= 757.130, but all I get now is static. Not even the slightest hint of a radio station. Not sure what else to do this is all new to me. confused  Any and all help would be appreciated. Thanks
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Re: Help!!!

Post by Wildcat445 on Thu Jun 19, 2014 2:50 pm

There is really not enough information to go on, but I can guess.  Did it work before you recapped it?  Have you verified that all your connections are correct and that solder joints are good?  Do you have a schematic for your set?  Is the antenna connected properly?  Did you clean all the controls, including the band switch, if any?  Let me see if I can find a schematic for your set so that I may be of more help.

Edit.....The schematic for this radio is in Riders 23-35. If you do not have a copy, and will PM me with your address, I will be happy to print and send you one. This is an AA5 radio. Perhaps the oscillator is not running. Did you wiggle the tubes against the chance of a bad tube connection? Did you test the tubes and replace any bad ones? What kind of test equipment do you have? You could turn this radio on, then turn on another radio and check for the squeal of the oscillator. If you need instructions how to do this, we can help you with that. There are not many parts in your radio, so not much to go wrong. It is a good set to learn on. Keep your chin up, we all started out the same way as you are. It will feel mighty good when you get this thing going. We are here to help.

WC

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Re: Help!!!

Post by frank1956 on Thu Jun 19, 2014 3:55 pm

Thanks for the response.The radio was not working when I got it, had a hum when I first turned it on. Replaced all the capacitors and the three Electrolytic. Plugged her in and same same just static, but no Hum. Replaced all the resistors and still static. I do have a schematic for this radio, but I am a GREEN HORN when it come to this. I just went back and ensured all the capacitors and resistors had a good connection and they seem too. I have not tested the tubes, but they all glow wish I know means nothing. The antenna seem to be connected properly the wire were only so long for each connection.

I will clean all the controls again, might have gotten something in them while I was working on it, also will wiggle the tubes to see what happens next. Again thanks for all the advice and hopefully I can get it running once more.
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Re: Help!!!

Post by Bill Cahill on Thu Jun 19, 2014 4:19 pm

Is this set a fifties radio with miniature tubes, and, small I F transformer cans? If so, likely, one of your IF cans has the dreaded capacitor leakage problem. We can help you here. We've all got experience with that problem. Laughing

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Re: Help!!!

Post by Bill Cahill on Thu Jun 19, 2014 4:20 pm

Dreaded Mica disease.

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Re: Help!!!

Post by Wildcat445 on Thu Jun 19, 2014 5:39 pm

The negatives of the electrolytic filter caps in this radio connect to common negative, which is one side of the power switch. They do not connect to chassis ground. I mention this since it is easy to make a mistake here. Mica disease is a possibility, but I don't feel we have enough evidence to convict the IF transformers just yet. A situation like this is where a signal generator comes in handy. You could inject a 400 cycle audio note, at the IF frequency, into the circuit just ahead, and just behind the IF transformers to see if they pass that signal. Then go to the antenna and do the same thing. You could also sub the 12BE6 converter tube to see if that makes any difference. Check for B+ on both IF transformers and also run some voltage measurements on the various tube elements. Pay particular attention to the grid voltage on the tube or tubes following an IF transformer. The grid on the 12BA6 IF amplifier is pin 1. Check on pins 5 & 6 on the 12AV6 for negative voltage, too. There should be negative voltage on the grids. Positive voltage on the grid or grids points more toward silver mica migration or Silver Mica disease. I'd like to be sure of our diagnosis before we put you thru a repair of SMD. Is the static just like white noise, or does it sound like lightning and thunder crashing? The latter would lend itself to the more dire silver mica migration diagnosis. Good luck.

WC

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Re: Help!!!

Post by 35Z5 on Thu Jun 19, 2014 7:11 pm

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Re: Help!!!

Post by frank1956 on Thu Jun 19, 2014 7:44 pm

Wildcat445 wrote:The negatives of the electrolytic filter caps in this radio connect to common negative, which is one side of the power switch.  They do not connect to chassis ground.  I mention this since it is easy to make a mistake here.  Mica disease is a possibility, but I don't feel we have enough evidence to convict the IF transformers just yet.  A situation like this is where a signal generator comes in handy.  You could inject a 400 cycle audio note, at the IF frequency, into the circuit just ahead, and just behind the IF transformers to see if they pass that signal.  Then go to the antenna and do the same thing.  You could also sub the 12BE6 converter tube to see if that makes any difference.  Check for B+ on both IF transformers and also run some voltage measurements on the various tube elements.  Pay particular attention to the grid voltage on the tube or tubes following an IF transformer.  The grid on the 12BA6 IF amplifier is pin 1.  Check on pins 5 & 6 on the 12AV6 for negative voltage, too. There should be negative voltage on the grids.  Positive voltage on the grid or grids points more toward silver mica migration or Silver Mica disease.  I'd like to be sure of our diagnosis before we put you thru a repair of SMD.  Is the static just like white noise, or does it sound like lightning and thunder crashing?  The latter would lend itself to the more dire silver mica migration diagnosis.   Good luck.

WC

The Static is more of the lighting- thunder. It seem to be worse when I mess with the on/off, volume switch. the higher the volume the more lighting-thunder effect. Lower less stormy weather.
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Re: Help!!!

Post by frank1956 on Thu Jun 19, 2014 10:23 pm

How do I check for the for the squeal of the oscillator with two radio's on at the same time?
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Re: Help!!!

Post by 35Z5 on Thu Jun 19, 2014 11:01 pm

The osc emits a signal 455Kc higher than what the dial is tuned... Sooo if it's set to 1000, the signal emitted will be 1455Kc(where you'd tune the operating radio)...
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Re: Help!!!

Post by Wildcat445 on Thu Jun 19, 2014 11:39 pm

Lightning-thunder, huh? That does not sound good. You really need to measure the grid voltage on the tube following the IF transformer for any sign of positive voltage. Leave the meter on long enough to make sure that there is no positive voltage in one of the "lightning" crashes. If you get the "lightning" crashing sound when you move the volume control, you could merely have a dirty or worn volume control. Good luck.

WC

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Re: Help!!!

Post by frank1956 on Fri Jun 20, 2014 1:02 am

Now that you mention it, I believe it could very well be the volume control. It does seem to do the lighting crash more when I mess with it.
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Re: Help!!!

Post by 35Z5 on Fri Jun 20, 2014 1:25 am

If it's not picking up any stations chances the volume control is all the problem are almost nil...
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Re: Help!!!

Post by Wildcat445 on Fri Jun 20, 2014 8:08 am

35Z5, you make a good point. We have veered off course concerning ourselves with the lightning crashing sound. The OP should measure the voltage on the grid of the converter tube, the 12BE6. If the oscillator is running, there should be from -5 to -15 (negative volts) on that grid. Zero or positive voltage would indicate a dead or dying oscillator, necessitating troubleshooting the oscillator section of the receiver. We still need some voltage readings on the grids of the tubes following the IF transformers. Plate voltage readings on the 12BE6 and 12BA6 would be helpful as well. Also measure resistance on the primary and secondary of both IF transformers. There should only be a few ohms on each one. "All voltages are taken from socket prongs to B-" which is one side of the power switch. Good luck.

WC

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Re: Help!!!

Post by frank1956 on Fri Jun 20, 2014 10:17 am

Thanks for all the advice, but I am just not sure how to proceed with this. How do I measure the volts? Do I use an ohms meter, volt meter? What is negative volts? What does B- mean?
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Re: Help!!!

Post by Wildcat445 on Fri Jun 20, 2014 11:25 am

You need to have a good voltmeter before you can do much more. Do you have a voltmeter? You can buy a usable meter to start at Home Depot or Lowes for less than $30.  

Please refer to the post just above, where I quote the directions off the schematic for measuring voltages.  B- is the point with the least potential in the chassis.  You will notice on the schematic a little triangle symbol.  Note that this symbol is shown on one side of the power switch.  Notice also that in several locations on the schematic, this triangle symbol is present.  That indicates that each point represented by the triangle symbol is tied to B-, which is one side of the power switch.  To measure positive DC voltage, you would set your meter to measure DC + voltage, set the range for higher than the greatest voltage expected, then put the red (+) probe on a tube socket prong you want to test, and the black (-) probe on one connection of the power switch (B-).  Hope this helps and good luck.

WC

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Re: Help!!!

Post by 35Z5 on Fri Jun 20, 2014 1:38 pm

At this point it may be easiest to disconnect pin #1 on the 12BA6 to see if the noise stops... If so the problem is in front if the 12BA6(12BE6/1st IF) if not it's behind it, either in the 2nd IF transformer, 12AV6 audio amp or (not likely) the 50C5 audio output...

None of this discounts the importance of WC's prev post, if you are going to attempt repairs you'll need to get familiar with terms and have some very basic equipment such as a volt/ohm meter... Can get one that's cheap enough from Harbor Freight... Seen them for as little as $2.99 on sale and while they are uber cheap, actually are dead on as far as accuracy... Plus if you smoke it no big loss, chalk it up to experience...


Tom
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Re: Help!!!

Post by frank1956 on Fri Jun 20, 2014 4:03 pm

I think I might have found the problem. Did not notice it until I was re-checking connections etc.





Last edited by frank1956 on Fri Jun 20, 2014 4:10 pm; edited 2 times in total (Reason for editing : Pictures)
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Re: Help!!!

Post by 35Z5 on Fri Jun 20, 2014 4:26 pm

Bumblebee .047 AC line cap, those should always be replaced as are prone to failing just as you see, possibly could start fire...

And the bad news??? Isn't likely your noise problem, as radio will operate without it.. Purpose is provide a ground so reception is better...
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Re: Help!!!

Post by Wildcat445 on Fri Jun 20, 2014 4:38 pm

Notice the blackened area around the end of the bumblee. It let out all the magic smoke when it went. And what Tom said. Good luck.

WC

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Re: Help!!!

Post by 75X11 on Fri Jun 20, 2014 4:52 pm

Excellent pics also!
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Re: Help!!!

Post by frank1956 on Fri Jun 20, 2014 5:24 pm

Thanks all. I will go get a volt meter and proceed from there. I now have a little better understanding of what I need to do. Will let you know what I come up with
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Re: Help!!!

Post by Bill Cahill on Fri Jun 20, 2014 9:09 pm

No, you don't use an ohm meter. The voltage on that grid should be a very low negative DC voltage. If you are getting a positive voltage, then, the I F transformer is bad with the silver mica disease.

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Re: Help!!!

Post by Wildcat445 on Sat Jun 21, 2014 10:06 am

Frank, I will be happy to fix your radio, if you will teach me how to post pictures as good as yours. Get a meter and run some voltage measurements that have been suggested. We are here to help. Good luck.

WC

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Re: Help!!!

Post by frank1956 on Sat Jun 21, 2014 10:46 am

Deal!!!
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Re: Help!!!

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