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 Post subject: Re: A sick Philco PT-2 on the bench
PostPosted: Dec Tue 05, 2017 4:15 am 
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Don

Radio doesn't follow the schematic exactly. Either way pin #4 can ground or go to AVC.

Try connecting a wire between pin #7 on 7C6 and pin #7 on 7B7. This may cause the radio to operate. Were any wires replaced?

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 Post subject: Re: A sick Philco PT-2 on the bench
PostPosted: Dec Tue 05, 2017 6:05 pm 
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Location: Johnstown, Ohio
I connected a lead to pins 7 of the tubes you noted but nothing came of it, no sparks, smoke or sound. I have not moved any wires or replaced any wire since I received this radio from eBay. This radio just sounds as dead as if it were not plugged in. I have checked continuity on all the wires I can get to in the chassis and they are no breaks in the wiring.

Don


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 Post subject: Re: A sick Philco PT-2 on the bench
PostPosted: Dec Wed 06, 2017 1:14 am 
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Don, going back to pins 3 and 4 on the 50L6, with the radio unplugged measure the resistance between those pins. You should get a low reading, which means the primary side of the audio transformer is OK. Just to be thorough.


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 Post subject: Re: A sick Philco PT-2 on the bench
PostPosted: Dec Wed 06, 2017 2:34 am 
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The resistance on pin 3and 4 of the 50L6 is 167 ohms.

Don


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 Post subject: Re: A sick Philco PT-2 on the bench
PostPosted: Dec Thu 07, 2017 2:44 am 
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According to Norm there should be a wire on pin 7 of 7A8, 7B7 and 7C6. If there is a wire from pin 7 of the 7C6 to pin 4 of the 7B7, what is on pin 7 of the 7B7?

Attachment:
PT2Cathodes.jpg
PT2Cathodes.jpg [ 172.22 KiB | Viewed 140 times ]


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 Post subject: Re: A sick Philco PT-2 on the bench
PostPosted: Dec Fri 08, 2017 2:07 am 
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Hi Folks,
I tried to upload an anotated picture of the underside of the chassis but I could not get the software to work tonight. Perhaps more research tomorrow will help. In the meantime I did confirm that there was no wire connect between 7B7 pin 7 and pin 7 of 7C6. As I had tested a few days ago I connected a jumper to these pins but it made no difference.

Don


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 Post subject: Re: A sick Philco PT-2 on the bench
PostPosted: Dec Fri 08, 2017 2:59 am 
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Hi Don!
On the PT-2 I had, the negative lead of the filter capacitors is connected to pin 7 of the 7C6. That would be B- .
Do you have that?

Now keep in mind that even though pin 7 of these tubes are connected to each other on the schematic (and to the B-) the actual wiring may take a round-about route. There doesn't need to be a wire directly from the 7C6 to the 7B6, but there should be a wire from pin 7 going somewhere in common with pin 7 of the other tubes.

Are the old rubber coated wires still in the set, or did somebody replace them?

At any rate, I don't think the connections to pin 7 of these tubes would cause it to be stone cold silent dead, as you described.


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 Post subject: Re: A sick Philco PT-2 on the bench
PostPosted: Dec Fri 08, 2017 7:39 pm 
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Hi SkyKing,

The ground from the electrolytics goes to pin 6 and then there is a stub of a wire that connects pin 6 to pin 7 of the 7C6. There is continuity between pin 7 of the 7C6 to pin 7 of the 7A8, although visually I cannot follow the wiring. One thing I noticed though is that on the center post of each tube socket there is a tab that touches each tub bottom, except for the 50L6. On all of these tubes that do have the tab there are wires soldered to the tab with the exception of the 35Z3. On this tab there appears to be remnants of solder as if at one time something connected there. I am not recognizing an indication of these tabs on the schematic, of course at this time I seem to be very unskilled at this. As for the old rubber insulation it is heavily cracked but hanging in there. I think that covers everything you ask about.
Thanks,
Don


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 Post subject: Re: A sick Philco PT-2 on the bench
PostPosted: Dec Sat 09, 2017 2:14 am 
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OK, it seems we can stop being concerned about the wires on pin 7. The fact that you get good readings and nobody has changed the wires out is sort of good news.
You didn't tell us if the radio ever worked when you first got it.


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 Post subject: Re: A sick Philco PT-2 on the bench
PostPosted: Dec Sat 09, 2017 2:30 am 
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I got the radio from eBay and the guy said it did not work. I try to buy these as they are good practice for me, sometimes too good, but I think it is the only way to learn.

Don


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 Post subject: Re: A sick Philco PT-2 on the bench
PostPosted: Dec Sat 09, 2017 3:27 am 
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Don

Could you measure voltage on pin #7 again? Pin #7 of 7C6 was reported to be zero while 7B7 and 7A8 was 15/16 volts. All three tubes should read zero. You could have continuity between these pins but at high resistance?

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 Post subject: Re: A sick Philco PT-2 on the bench
PostPosted: Dec Sat 09, 2017 4:43 pm 
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Old Tube wrote:
The ground from the electrolytics goes to pin 6 and then there is a stub of a wire that connects pin 6 to pin 7 of the 7C6.
Don


I am very carefully looking at some pictures I took of a PT-2. I have the ground from the electrolytics going to pin 7 and the little stub of wire you mentioned going to pin 8. Can you recount those pins? The electrolytics do NOT connect to pin 6.


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 Post subject: Re: A sick Philco PT-2 on the bench
PostPosted: Dec Sun 10, 2017 1:45 am 
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This is an answer to Norm's question. The DCV on pin 7's of the 7B7 and 7A8 were 20 and 21, respectively, with the B- being the ground of the electrolytics. There was no voltage on the 7C6. I checked the ohms on both pin 7's (while I was checking the voltage) and it was 103 ohms each, I do not know if this adds anything to the issue.

Don


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