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 Post subject: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 1:49 am 
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I'm 12 years old and need help restoring a philco radio. I posted a topic on this radio a little while ago. like everyone said i replace the 450v 4uf and 12uf capacitors and all the wax capacitors and i still have the same problem, the transformer heats up and no sound comes out. under the chassis there is a 20uf 450v capacitor that i cannot find on the schematic. i think someone added it later. the capacitor was put across the 12uf 450v capacitor but the 12uf was still attached. If anyone thinks they know the problem please help!


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 1:55 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Albuquerque, NM 87123
Remove the rectifier tube and turn the radio on; wait a few minutes and see if the transformer still gets hot. If it does, then the transformer is bad. If it just gets warm then there is an additional problem that needs to be found.


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 2:04 am 
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i've tried that already when i take it out the tube doesn't get hot.


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 3:10 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Albuquerque, NM 87123
I take it you mean the transformer doesn't get hot.

You have a partial short on the power supply. I would suspect the .01uf capacitor on pin 2 of the 41 (audio output) tube.

Your rectifier should be an 84. It's possible you have a shorted 6A7 tube, but not likely.


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 1:23 pm 
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Where are you located? There might be a radio club or someone nearby that can help you.


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 2:13 pm 
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efernandez wrote:
I'm 12 years old and need help restoring a philco radio. I posted a topic on this radio a little while ago. like everyone said i replace the 450v 4uf and 12uf capacitors and all the wax capacitors and i still have the same problem, the transformer heats up and no sound comes out. under the chassis there is a 20uf 450v capacitor that i cannot find on the schematic. i think someone added it later. the capacitor was put across the 12uf 450v capacitor but the 12uf was still attached. If anyone thinks they know the problem please help!


Just ADDING an additional capacitor was somewhat common method of repairing "Back in the Olden Days" Today you need to follow the correct value parts shown on your schematic and REMOVE any "Extra" ones that may be in the radio. If replacing a metal can capacitor it is OK to leave the negative side of the can connected but be sure to disconnect the positive end so that capacitor is no longer active.

Your schematic
http://www.nostalgiaair.org/pagesbymodel/236/M0013236.pdf

Check ohms from pin2 of the 41 tube to chassis. It should be in the megohm range. If it is in the 4000 ohms or less area then you have some miswire or partial short someplace in the circuitry of the radio.

John k9uwa

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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 2:23 pm 
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Yes, that what I meant sorry for the typo. I have extra capacitors so I'll replace it and by luck have an extra working 6a7 so I'll replace that too. Thanks for the help.


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 2:42 pm 
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I measured it and got around 3.5 megaohms.


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 2:51 pm 
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efernandez wrote:
I measured it and got around 3.5 megaohms.


Try this next. Connect up your DC voltmeter to pin2 of the 41 tube and black lead to chassis. Remove all the tubes except the 84 and the 41 tube. Turn the radio on and watch the B+ voltage on your meter. It should rise to above 200 volts and then settle back to around 200 volts after the 41 tube warms up. If that is what it does then let it run that way for a bit and observe the power transformer temperature. If it doesn't follow those voltages then perhaps the 84 tube itself is bad? Or an internal short in the 41 tube.

Is it possible you have one of the new electrolytic capacitors connected backward? Correct would be if the Plus end of each is connected to either side of the field coil. Negatives second one it to chassis and first one is to center tap of HV winding in the transformer.

John k9uwa

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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 3:11 pm 
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There is around 1-2 volts. I found the problem!


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 3:22 pm 
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efernandez wrote:
There is around 1-2 volts. I found the problem!


Probably a litic turned backward. If so it is a wonder it didn't explode and for sure if that was the problem it shouldn't be used again but should be replaced.
John k9uwa

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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 3:34 pm 
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I checked multiple times they are wired correctly.


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 3:46 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Albuquerque, NM 87123
And, what was the problem? And does the radio work?


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 3:49 pm 
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The transformer heats up and no sound comes out.


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 4:04 pm 
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efernandez wrote:
There is around 1-2 volts. I found the problem!


So what was the problem?
John k9uwa

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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 4:17 pm 
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I think the 41 tube is broken when i take it out and flip it around i hear something broken in side.


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 4:23 pm 
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do you guys think that could be the problem?


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 4:41 pm 
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Location: Leo, IN or Zellwood, FL
efernandez wrote:
I think the 41 tube is broken when i take it out and flip it around i hear something broken in side.


With the 41 tube OUT of its socket check DC voltage from pin 2 to chassis and pin3 to chassis on the 41 tube socket. Also check DC voltage from pin 4 of the 84 tube socket to chassis. Each of those should read over 200 volts DC. If still 1 to 2 volts Then pull out the 84 tube switch the meter over to read AC voltage. Connect one lead of the voltmeter to the center tap of the high voltage winding on the transformer. It should be the same point as the negative lead of the first Litic capacitor. Other meter lead to pin2 of the 84 socket. It should read about 300 volts. Then turn it off and connect meter to pin3 of the 84 socket and again check voltage. It also should read about 300 volts.
Next check the 6 volt winding of the transformer AC meter to pins 1 and 5 of the 84 tube socket.

Tell us what voltages you read in the above tests.
JOhn k9uwa

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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 5:10 pm 
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the first tests i got 1-2v dc on all of them, the second one i got 308-310v ac for both tests, and the third i got 6.5v ac.


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 8:15 pm 
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efernandez wrote:
the first tests i got 1-2v dc on all of them, the second one i got 308-310v ac for both tests, and the third i got 6.5v ac.


I am beginning to think that the 84 tube is the culprit perhaps? And probably also the 41 tube. Any chance in your tube stash that you might have another 84 tube? or perhaps a 6X5 tube? Or a couple 1N4007 diodes?

Also do you have a variac or a dim bulb tester?

John k9uwa

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