I have been laboring over a Zenith 12S568 for quite some time. Most of the wires under the chassis were cracked and shorting out. I have replaced 90% of the wires with new one, recapped it, and checked the tubes. When I tried to fire it up for the first time no tubes lite up and the dial light did not glow. I did some checking and someone before me rewired the rectifer for a 5Y3 instead of the 5Y4 that the schematic calls for. I put in a 5Y3 and still nothing. The 5Y3 gets warm, but none of the other tubes. R21 got so hot that it started smoking so I replaced it, but it gets hot enough to smoke as well. I have checked the feild coil and it registers 575 ohms. I am at a lost where to go from here and I would appreciate some of your wisdom. Thanks, Ron

:I have been laboring over a Zenith 12S568 for quite some time. Most of the wires under the chassis were cracked and shorting out. I have replaced 90% of the wires with new one, recapped it, and checked the tubes. When I tried to fire it up for the first time no tubes lite up and the dial light did not glow. I did some checking and someone before me rewired the rectifer for a 5Y3 instead of the 5Y4 that the schematic calls for. I put in a 5Y3 and still nothing. The 5Y3 gets warm, but none of the other tubes. R21 got so hot that it started smoking so I replaced it, but it gets hot enough to smoke as well. I have checked the feild coil and it registers 575 ohms. I am at a lost where to go from here and I would appreciate some of your wisdom. Thanks, Ron

Forgot to give the link for the Schematic http://www.nostalgiaair.org/PagesByModel/727/M0024727.pdf
:

Have you replaced all the electrolytic filter caps and the paper/wax caps?

If not the filter caps could be bad..

A 5y4 and 5y3 can be wired to be interchangeable so check if the socket has been configured that way.

Before you check the B+ you should check the tube filament wiring. And to be sure the 6volt AC winding is putting out 6vac.

Try removing the rectifier while you check the 6 volt filament circuit.

When you find the problem there and correct it and all tubes light.. and after being sure to replace the caps.. then reinstall the rectifier and test B+.

:Have you replaced all the electrolytic filter caps and the paper/wax caps?
:
:If not the filter caps could be bad..
:
:A 5y4 and 5y3 can be wired to be interchangeable so check if the socket has been configured that way.
:
:Before you check the B+ you should check the tube filament wiring. And to be sure the 6volt AC winding is putting out 6vac.
:
:Try removing the rectifier while you check the 6 volt filament circuit.
:
:When you find the problem there and correct it and all tubes light.. and after being sure to replace the caps.. then reinstall the rectifier and test B+.
:
:
Thanks for the help. I have replaced all of caps including the electrolytic and I made sure they were installed correctly. I will remove the rectifier and see if I have 6 volts coming off the power tranformer.
Ron

Actually the 6vAC winding is usually good so there must be a wiring problem in the 6 voltAC filament circuit.

Easy way to trouble shoot this is to remove all the tubes and see that the 6valts is Ok.. it will read high (7-8v)with no tubes to load it down properly so don't worry.

Chech the filament continuity of each 6 volt tube w/an ohm meter while they are out.
Then if you also do get good voltage from that filament winding ... then try replacing one 6v tube to see if it lights up. Continue with one tube at a time to see if each one light properly till you find the wiring error.
Also remove and check the pilot lamp and then check the lamp socket for shorts too.

:Also remove and check the pilot lamp and then check the lamp socket for shorts too.

Hi Ron

Filaments are often heavy green wires from a power transformer. They will connect to pins #2 and #7 on your tube sockets.

Your filament winding is center tapped and connected to chassis. Check where center tap is connected to chassis. Sometimes the center tap is brought out of a transformer as two wires. Both must make good connection to chassis.

Very little else can be wrong with a filament winding. It will be heavy wire so can't burn out easily. Not shorted or you would be seeing smoke in less than a minute.

Norm

:I have been laboring over a Zenith 12S568 for quite some time. Most of the wires under the chassis were cracked and shorting out. I have replaced 90% of the wires with new one, recapped it, and checked the tubes. When I tried to fire it up for the first time no tubes lite up and the dial light did not glow. I did some checking and someone before me rewired the rectifer for a 5Y3 instead of the 5Y4 that the schematic calls for. I put in a 5Y3 and still nothing. The 5Y3 gets warm, but none of the other tubes. R21 got so hot that it started smoking so I replaced it, but it gets hot enough to smoke as well. I have checked the feild coil and it registers 575 ohms. I am at a lost where to go from here and I would appreciate some of your wisdom. Thanks, Ron
:

:Hi Ron
:
: Filaments are often heavy green wires from a power transformer. They will connect to pins #2 and #7 on your tube sockets.
:
: Your filament winding is center tapped and connected to chassis. Check where center tap is connected to chassis. Sometimes the center tap is brought out of a transformer as two wires. Both must make good connection to chassis.
:
: Very little else can be wrong with a filament winding. It will be heavy wire so can't burn out easily. Not shorted or you would be seeing smoke in less than a minute.
:
:Norm

Norm:
please 'splain something to me. The schematic on this site for 12S568 doesn't compare with what you guys are discussing. The schematic here has indirectly heated cathodes on the rectifiers, 6X5s I think, and no 5Volt winding a'tall.
Lewis

:
::I have been laboring over a Zenith 12S568 for quite some time. Most of the wires under the chassis were cracked and shorting out. I have replaced 90% of the wires with new one, recapped it, and checked the tubes. When I tried to fire it up for the first time no tubes lite up and the dial light did not glow. I did some checking and someone before me rewired the rectifer for a 5Y3 instead of the 5Y4 that the schematic calls for. I put in a 5Y3 and still nothing. The 5Y3 gets warm, but none of the other tubes. R21 got so hot that it started smoking so I replaced it, but it gets hot enough to smoke as well. I have checked the feild coil and it registers 575 ohms. I am at a lost where to go from here and I would appreciate some of your wisdom. Thanks, Ron
::
:

http://www.nostalgiaair.org/PagesByModel/727/M0024727.pdf

:I have been laboring over a Zenith 12S568 for quite some time. Most of the wires under the chassis were cracked and shorting out. I have replaced 90% of the wires with new one, recapped it, and checked the tubes. When I tried to fire it up for the first time no tubes lite up and the dial light did not glow. I did some checking and someone before me rewired the rectifer for a 5Y3 instead of the 5Y4 that the schematic calls for. I put in a 5Y3 and still nothing. The 5Y3 gets warm, but none of the other tubes. R21 got so hot that it started smoking so I replaced it, but it gets hot enough to smoke as well. I have checked the feild coil and it registers 575 ohms. I am at a lost where to go from here and I would appreciate some of your wisdom. Thanks, Ron
:
Gentlemen, Thank you for your help. The radio is playing as I type. I made a very dumb mistake. When I was replacing the wires I hooked up the wire that went to pin 7 of the 6J5 to the wrong connector on a terminal strip. I looked closer and discovered that the the one of the wires that supplies the 6 volts was hooked up to nothing, so the circuit was not completed. At any rate I move the wire and the radio is playing. I cannot tell you how satisfying this is. I have put in countless hours replacing all of the wires and capacitors and this is one radio I really wanted to get up a running. As you probabaly know this Zenith has a shutter dial! Thanks again for the help.

Yes ... very satisfying ..especially when one can do all the work and reap the rewards!!! Always a joy to hear a nice old radio come back to life again!!!

::I have been laboring over a Zenith 12S568 for quite some time. Most of the wires under the chassis were cracked and shorting out. I have replaced 90% of the wires with new one, recapped it, and checked the tubes. When I tried to fire it up for the first time no tubes lite up and the dial light did not glow. I did some checking and someone before me rewired the rectifer for a 5Y3 instead of the 5Y4 that the schematic calls for. I put in a 5Y3 and still nothing. The 5Y3 gets warm, but none of the other tubes. R21 got so hot that it started smoking so I replaced it, but it gets hot enough to smoke as well. I have checked the feild coil and it registers 575 ohms. I am at a lost where to go from here and I would appreciate some of your wisdom. Thanks, Ron
::
:Gentlemen, Thank you for your help. The radio is playing as I type. I made a very dumb mistake. When I was replacing the wires I hooked up the wire that went to pin 7 of the 6J5 to the wrong connector on a terminal strip. I looked closer and discovered that the the one of the wires that supplies the 6 volts was hooked up to nothing, so the circuit was not completed. At any rate I move the wire and the radio is playing. I cannot tell you how satisfying this is. I have put in countless hours replacing all of the wires and capacitors and this is one radio I really wanted to get up a running. As you probabaly know this Zenith has a shutter dial! Thanks again for the help.
:

Ron, a suggestion I have learned. When start working on a radio, troubleshoot if necessary to get it working, at least after a fashion - before rewiring or replacing caps, etc. Then replace wires or caps one at a time and check that the radio still plays after each step.

This approach can save some agony.

:Ron, a suggestion I have learned. When start working on a radio, troubleshoot if necessary to get it working, at least after a fashion - before rewiring or replacing caps, etc. Then replace wires or caps one at a time and check that the radio still plays after each step.
:
:This approach can save some agony.
:

There's another reason for doing this. It will help you learn how things work. Preactical experience along with some study of the theory and you'll soon be able to fix almost anything. The best test instrument you will ever have is the one between your ears. The more you put into it the more useful it becomes.

:Ron, a suggestion I have learned. When start working on a radio, troubleshoot if necessary to get it working, at least after a fashion - before rewiring or replacing caps, etc. Then replace wires or caps one at a time and check that the radio still plays after each step.
:
:This approach can save some agony.
: