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 Post subject: rectifier behaving badly
PostPosted: Feb Fri 20, 2004 12:42 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 219
Location: Florida
Hi guys:<P> I just got an Atwater Kent 944, but when I plug it in I get the usual evidence that the unit is working but no stations are received. I assume I have some bad caps, and I will check them.<BR> Question. The rectifier tube (a # 80) lights up for a few minutes and then goes dark. I have never seen this behavior before. Wiggling the tube does not light it, but it will light again if I let the radio sit for a few minutes. The tube tests strong. Any thoughts on this? Is the socket bad or is it a failing resistor, or what? <P>Thanks!<P>Karen <P>------------------<BR>Karen


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 Post subject: rectifier behaving badly
PostPosted: Feb Fri 20, 2004 12:45 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 27867
Location: Detroit, MI USA
It might be the socket, or a bad solder connection on the socket, or even inside one of the tube pins. Somewhere along the way, the 5 volts of AC from the power transformer is not making its way to the filament inside the tube.<BR>Try testing it in the tube tester for a long time, to let it heat up enough to see whether the intermittent is in the tube.<P>------------------<BR>Dennis


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 Post subject: rectifier behaving badly
PostPosted: Feb Fri 20, 2004 3:51 am 
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Location: Maryland 20709, USA
Hi Karen,<P>Well... slap it up 'side o' the head <IMG SRC="http://antiqueradios.com/forums/smile.gif"> (Sorry, couldn't resist <IMG SRC="http://antiqueradios.com/forums/smile.gif"> )<P>It sounds like a connection is opening up in the radio somewhere due to heat. It might be inside the transformer, or it might be in or around the rectifier socket. There's a simple test that might narrow it down:<P>With the radio off, remove the rectifier, leaving all other tubes in place. Turn the radio on and let it run for a few minutes, two or three times as long as it takes for the problem to show up. Turn it off, insert the rectifier, and immediately turn it back on.<P>If the rectifier comes on, then goes off after a while as it did before, the problem is likely at the rectifier tube socket. If it won't come on at all, the problem is likely inside the transformer.<P>No guarantees, but this might narrow it down. If it appears to be the socket, try resoldering all connections, and make sure you have good contact pressure for all pins. Also, wiggle each socket pin and make sure it's not broken and just making intermittent contact within the socket insulator.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR> <A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A>


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 Post subject: rectifier behaving badly
PostPosted: Feb Fri 20, 2004 4:27 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 219
Location: Florida
Thanks guys. <P>Well, I didn't slap it, but I did wiggle it a bit while it was plugged in and hot. Nothing happend. :-) <P>I will give your suggestions a try and report back. <P>------------------<BR>Karen


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 Post subject: rectifier behaving badly
PostPosted: Feb Fri 20, 2004 6:39 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 11474
Location: Valley City ND USA
A smack is worth a thousand tests sometimes. I would have said "clout", but I Have been corrected by one of our more learned friends. [I appreciate that] I had thought it to be a more delicate manouver. <P>The term clout seems to involve a hammer.......Ya!....Give it a clout!<P>------------------<BR>terry h


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 Post subject: rectifier behaving badly
PostPosted: Feb Sat 21, 2004 12:18 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4866
Location: Gainesville, Florida
Its a lot easier to troubleshoot after all the caps are replaced. Try another variant, take all the other tubes out but the 80 just to see what happens. Probably nothing but just in case. Im messing with a Philco 47-404 without replacing the caps first just to see what each one does individually replaced. Im having trouble with the power supply low voltage. I thought that you were not allowed to mess with radios anymore or is it a possiblity now. Getting any better at soldering?


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 Post subject: rectifier behaving badly
PostPosted: Feb Sat 21, 2004 11:48 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 219
Location: Florida
Hi guys:<P> Well, I recapped the radio save for two caps in the chassis that I want to ask you about. The radio plays well for 10 minutes and then the rectifer tube goes out. This <BR>is after I tightened the sockets and checked the tube in the tube tester (it stays lit in the tester). <P> Something is overheating or failing. One odd looking cap (C14 -- .01 UF) is flat and rectangular. It is a metal strip wraped in wax, and I believe it's part of the transformer primary winding. Should I go ahead and replace it? Also, there is a small flat rectangular metal cap (C4 -- 125 pf). Should I go ahead and replace that one too? According to the parts list, the only mica cap is on top of the chassis. <P> Finally, if replacing these two caps doesn't help, which pins should I be checking in the rectifier socket to determine if the transformer is overheating and shutting down? There are four pins P F P F. What should the correct voltage be?<P>Thanks guys. :-) <P>PS: yes, I'm still working on radios. Though I won't have time for it once the baby comes. My soldering is okay. Nothing to brag about. <P>------------------<BR>Karen


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 Post subject: rectifier behaving badly
PostPosted: Feb Sun 22, 2004 12:13 am 
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Location: Livermore, CA
Hi Karen<P> Try resoldering the two large pins on your 80. <P>------------------<BR>Norm


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 Post subject: rectifier behaving badly
PostPosted: Feb Sun 22, 2004 3:12 am 
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Location: Maryland 20709, USA
Hi Karen,<P>The two fat pins, marked F, are the filament pins. You should have 5 volts AC measured on those two pins.<P>But be VERY CAREFUL... you also have B+ on those pins. If you try to measure the AC voltage, take care that you don't touch the chassis or anything else while doing so. And use one hand for both probes, like chopsticks.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR> <A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A>


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 Post subject: rectifier behaving badly
PostPosted: Feb Sun 22, 2004 4:06 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 219
Location: Florida
Hi guys:<P>Norm, I resoldered the four socket pins, and I think I've got a good connection to all the pins of the tube. An interesting thing happened though, now the tube is dead. It won't lite in the radio or in my tester. No shorts, it's just plain dead. I'm wondering if one of the pins on the tube might be bad and that is the source of the problem. I don't have another # 80 handy to test. Can I heat the pins lightly with a torch to try and restore the internal connection inside the pins, or is the tube lost?<P>Thanks!!! <P>------------------<BR>Karen


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 Post subject: rectifier behaving badly
PostPosted: Feb Sun 22, 2004 4:45 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 935
Location: Columbus, OH USA
It may be a bad 80 base connection. You can reheat the pins to see if the connection can be resurrected. However, wiggling the tube didn't affect the connection, so my money would be on a new 80 tube :-(<P>Proud father of an 8 month old boy-<BR>Brad in Ohio<P>------------------<BR>


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 Post subject: rectifier behaving badly
PostPosted: Feb Sun 22, 2004 5:08 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 219
Location: Florida
Hi Guys:<P> I measured the filament pins and got five volts. Is there any reason to think that the B+ voltage has failed? Should I measure it? <P> I'll heat the pins and see if that helps.<P>You guys are the best!<P>Cheers!<P><P>------------------<BR>Karen


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 Post subject: rectifier behaving badly
PostPosted: Feb Sun 22, 2004 5:18 am 
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Location: Maryland 20709, USA
Hi Karen,<P>Yes, you can measure the B+ and see if it's there, or if it went south for the winter <IMG SRC="http://antiqueradios.com/forums/smile.gif"><P>But the original problem reported was that the rectifier went dark. If that is still happening, then you would have no B+. If the rectifier filament is lit, you should have B+.<P>You can measure it at the filter capacitors or at the plate of the audio output tube.<P>Another possible problem area would be the speaker connector and socket. Problems there could cause loss of B+, but would not cause the rectifier to go dark.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR> <A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A>


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 Post subject: rectifier behaving badly
PostPosted: Feb Sun 22, 2004 8:33 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 219
Location: Florida
Hi Guys:<P> Well, it turns out that it was one of the pins on the tube. I heated them with my soldering iron and that did it. The rectifier tube is back and tests strong. And the radio plays well. <P> The only remaining issue is that the radio is vibration sensitive. Anywhere I tap creates a lot of noise. Any thoughts on the cause?<P>As always, thank you very much gentlemen.<BR> <P>------------------<BR>Karen


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 Post subject: rectifier behaving badly
PostPosted: Feb Mon 23, 2004 12:12 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1479
Location: Cambridge MN USA
Most likely a microphonic tube. Tap each one (the rectifier won't cause this, though) until you get a very distinctive ping that's different from tapping the rest. That's the tube you'll need to replace.<P>Scott Todd<BR><P>------------------<BR>


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