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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 10:00 pm 
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Joined: Jun Sat 08, 2019 12:04 am
Posts: 17
I think I'll replace those tubes. I don't have much of a stash as I'm new to antique radios. Why would I need a 6X5 tube my radio doesn't have one of those I think your talking about a 6A7 and I do have extras of those. Why would I need diodes? I don't have a variac and dont have a dim bulb tester but I could make a dim bulb tester if I had to.


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 11:26 pm 
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Joined: Jun Wed 14, 2006 11:49 pm
Posts: 7661
Location: Leo, IN or Zellwood, FL
efernandez wrote:
I think I'll replace those tubes. I don't have much of a stash as I'm new to antique radios. Why would I need a 6X5 tube my radio doesn't have one of those I think your talking about a 6A7 and I do have extras of those. Why would I need diodes? I don't have a variac and dont have a dim bulb tester but I could make a dim bulb tester if I had to.


I was thinking of ways to continue testing the radio even though the 84 tube is probably bad and the 41 is bad. 5 clip leads and a 6x5 will replace an 84 tube as a way to test the power supply of the radio. Or a pair of 1N4007 diodes could be clip leaded to temporarily replace the 84 tube.

So yes order some tubes and while waiting for them to arrive perhaps get together a dim bulb tester. It is nice to be able to start up a non-working radio at a reduced voltage or to know that the current draw is higher than it should be. I sure beats smoking power transformers.

Example on this radio. With a dim bulb tester connected to the radio. Start the radio up without the 84 tube and the 41 tube and observe the dim light bulb. Next plug in the 84 tube and if the brilliance of the bulb comes up considerably then you know that 84 tube has some short or something wrong with it. Your AC voltages of the high voltage winding say that it is OK as both sides are 300+ volts and very close to being the same. Yet when the 84 is plugged in you have 1 volt DC at the cathode of the 84 tube indicating that it isn't doing its job. Further if it creates a large load difference on the line and the transformer then something in the tube is probably shorted. It is possible that someone tried to run the radio with very badly shorted internally electrolytic capacitors and that would increase dramatically the current draw on the 84 tube and the transformer. Damaging the tube is an OK so I have to spend a few bucks for a tube but hopefully the power transformer isn't damaged as that gets both expensive as well as a lot more work to replace it. Or perhaps the loose stuff inside the 41 tube shorted out the plate to cathode or screen grid to cathode or to parts of the filament in the tube. All of which would again create an excessive load on the high voltage winding ... croak the 84 tube and heat the transformer.

John k9uwa

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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Thu 20, 2019 11:50 pm 
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Joined: Jun Sat 08, 2019 12:04 am
Posts: 17
Do you know of any websites that sell tubes #41 and #84? I cannot seem to find any. Anyway thanks for all you help John I really wouldn't have any idea on how to fix it without your help!


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 Post subject: Re: Problems with a philco 38-12, need help!!
PostPosted: Jun Fri 21, 2019 12:11 am 
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Joined: Jun Wed 14, 2006 11:49 pm
Posts: 7661
Location: Leo, IN or Zellwood, FL
efernandez wrote:
Do you know of any websites that sell tubes #41 and #84? I cannot seem to find any. Anyway thanks for all you help John I really wouldn't have any idea on how to fix it without your help!


Tube dealers. I deal with a few of them in no particular order.
ESRC tubes in Orlando Florida http://www.esrcvacuumtubes.com/ 41 $10.00 84 $7.00
Bob Dobush http://findatube.com/ New and Used Tested 84 tubes $6.00 and $3.00 new and used tested 41 $6.40 and $3.00

I would go with Bob Dobush for these two. Either New or Tested Used. Plus shipping whatever he gets for that part.
John k9uwa

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http://www.JohnJeanAntiqueRadio.com


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