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#1
08-31-2019, 07:55 PM
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Self-destructing HV rectifier tube
Got a 1968 Magnavox color the other day. I noticed it had no hv, so I opened up the hv cage and saw the rectifier tube was in half. I replaced it and hv came up with no issues. My question is, how does this happen? Perhaps some major arcing inside the tube? Maybe a factory defect? What is your thinking? BTW, the tube is a 3CU3.
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Your good times will bring me down 
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#2
08-31-2019, 08:51 PM
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30 years ago..." Damn it the picture went out in the first inning...well let's just crank the volume to drown out that arcing noise and listen to the rest"... People do goofy stuff sometimes.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
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#4
09-01-2019, 12:49 AM
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That was some nice internal damage! That thing is cooked! I'd say it ran while cooking away. I lf the set is running and flyback looks ok and not overheating then you're good to go. How is the wax drippage? You said "Magnavox", so I just have to ask?
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Honey, turn on the tv.. I'm cold!
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#5
09-01-2019, 09:01 AM
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Dodged the bullet on that one. One reason you should never, ever leave a vintage TV running unattended, even for a minute. 'Specially color.
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#6
09-01-2019, 11:47 AM
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That 3CU3 is the first HV rectifier tube I have ever seen with damage like yours had. When you said the tube was "in half", I immediately looked at the attachment and, sure enough, saw the tube's glass envelope literally broken in half. I wonder what caused that type of damage, although my best guess is the tube was severely overloaded somehow. Whatever it was, the overload must have been severe enough, and then some, to cause the tube to come close to exploding. In fact, I am surprised the tube's envelope did not shatter, rather than splitting in two as it did.
It could also be, as MadMan said in his post, that the tube had a manufacturing defect and just broke open. If the TV now works as normal, with normal HV, I wouldn't give it a second thought. BTW, 1968 was about the time everyone was beginning to worry about X-rays from color televisions. I mention this because of the warning on the base of the broken 3CU3 regarding the possibility of the tube emitting high, even harmful levels of X-rays if the tube was not properly shielded. This problem was addressed and apparently corrected, however, by about the mid-'70s (my best estimate), which should have set the collective public's minds at ease. Of course, this (X-ray radiation) cannot occur with today's flat screen televisions since there are no tubes in these sets, and the voltages found in such TVs are nowhere near the kilovolt range. Also, I can now understand why, in the late '60s-'70s during the X-ray scare, parents often told their children not to sit too close to the TV screen since, as I said above, there was a potential X-ray hazard with color sets of that era. Even today, with flat screens, kids are being warned not to sit too close to the set because of the possibility (even the likelihood) of eyestrain.
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Jeff, WB8NHV Collecting, restoring and enjoying vintage Zenith radios since 2002 Zenith. Gone, but not forgotten. Last edited by Jeffhs; 09-01-2019 at 12:35 PM.
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#7
09-01-2019, 12:29 PM
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The horiz out really must've been red-plating and it sucked in the side of the tube and cracked it. They were lucky it didn't take out the flyback. 
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#9
09-03-2019, 06:03 PM
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Linear Mode
