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Old 06-25-2018, 06:40 PM
Titan1a Titan1a is offline
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No more magic smoke.

My Zenith 11S474 console started making noises similar to putting a stylus on a bad record then died and started smoking. At least I know the power transformer is still good.
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Old 06-25-2018, 09:16 PM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by Titan1a View Post
My Zenith 11S474 console started making noises similar to putting a stylus on a bad record then died and started smoking. At least I know the power transformer is still good.
There is two different versions of the Zenith 11-S-474. One has ten tubes and the other has eleven tubes. I have two of the ten tube chassis.
The only difference between the two is the first audio and detector circuit.
The eleven tube job has a 6J5 and a 6F5 and the ten tube uses a 6Q7 for both functions.
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Old 06-25-2018, 10:53 PM
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Quote:
Originally Posted by Titan1a View Post
My Zenith 11S474 console started making noises similar to putting a stylus on a bad record then died and started smoking. At least I know the power transformer is still good.
Did you change the rubber wiring to the tuning eye? Some sets had 1-3 0f the eye tube wires usually including the B+ as rubber the rubber dries, cracks, and flakes off (especially where the eye harness passes through chassis, ask me how I know ) shorts B+ to ground and things start to smoke...

If that ain't your issue, pull the rectifier tube, if that stops the smoke check the resistance to ground of the B+ rail. The resistance should be higher than the result of dividing the B+ voltage (probably 450V) by the B+ current (probably less than 0.150A). If the B+ to chassis resistance is low, go to each point things connect to the B+, unhook everything, measure the individual disconnected paths and follow the path of least resistance to find the short.
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Old 06-26-2018, 08:09 AM
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init4fun init4fun is offline
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At least I know the power transformer is still good.

How did you determine the PT is still good ?
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Old 06-26-2018, 06:30 PM
Titan1a Titan1a is offline
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After turning the power off I turned it back on quickly. 6E5 tube lit up. I know; not a good practice.
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Old 06-26-2018, 07:26 PM
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init4fun init4fun is offline
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After turning the power off I turned it back on quickly. 6E5 tube lit up. I know; not a good practice.
Oh I'm not gonna chide you for the quickie "one more time" test , lots of folks can't seem to resist that , but the fact that the PT still passed power along to it's secondary windings after being overloaded does not mean that the overloaded transformer wasn't damaged . When a PT gets too hot and begins baking off the enamel insulating the windings , those windings begin to successively short together and the transformer will never again pass anything close to it's rated current without overheating . If it was in fact the transformer that let out the magic smoke it's likely done for (well known for certain models of Zenith in those years with somewhat , er , underrated PTs) even though it still appeared functional after the incident .

You can HOPE it's still good , but till it's seen properly performing in real time operating conditions (like the repaired radio running an hour without the PT reaching Nuke plant temperatures) there is no automatic judgement of "the 6E5 lit so the PT is fine" .
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Old 06-26-2018, 08:42 PM
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Originally Posted by init4fun View Post
If it was in fact the transformer that let out the magic smoke it's likely done for (well known for certain models of Zenith in those years with somewhat , er , underrated PTs) even though it still appeared functional after the incident .
Most of the Zenith power transformer failures of the era were caused by the infamous 6X5 rectifier tubes shorting. No radio transformer was meant to take having its high voltage secondary shorted (which the 6X5s often did when they failed).

I completely agree with the rest of your advice.



Do NOT power it up with the rectifier tube installed until you are confident that you've found and fixed the problem...If there is any rubber wiring remaining in the set I strongly suggest replacing it...You never know when/where/how it will short, and if you want to use the set regularly the rubber should go as preventative maintenance.
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Old 06-26-2018, 11:26 PM
Titan1a Titan1a is offline
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Both 6X5 tubes were previously replaced with solid state units incorporating surge suppressors. Before I reapplied power I felt the PS which was only mildly warm.
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