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#1
03-08-2016, 09:34 AM
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1968 Magnavox Astronomic Magna color 25" combo tube question
Back when I piced this up, I noticed it needing the 6JE6C tube. There was also a smaller one to the left of it needing replaced but I can get to the back of it right now although I do have pics taken at the time I got it. Does anyone know what tube that would be? Supposedly, it's what caused the large one to fail.
Last edited by pac.attack76; 07-14-2016 at 02:45 PM. 
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#2
03-08-2016, 10:17 AM
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Hopefully, the flyback is alright.
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#4
03-08-2016, 12:35 PM
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The smaller tube is likely the horizontal oscillator. If this tube fails, it will cause the 6JE6C output tube to fail as well due to loss of grid bias. The output tube's plate current will rise uncontrollably without this bias voltage present on the control grid, destroying the tube in short order. Replace the horizontal oscillator tube first, before anything else. It might not be a bad idea to replace the output tube at the same time; it may have been damaged when the oscillator tube failed.
Note as well if the horizontal oscillator stops for any reason, in addition to damaging or destroying the output tube the power transformer could burn out as well. This is caused by the excessive current drawn by the HO tube without grid bias. Do not operate the TV if the oscillator tube is defective; there is no point in doing so anyway, since there will be no raster if there is no high voltage. All TVs made after about 1950 derive the CRT's high voltage from the horizontal scanning and therefore depend on the horizontal oscillator and output stages' correct operation; if either malfunctions or fails for any reason, the HV will stop as well and, as I mentioned, the power transformer could be damaged.
__________________
Jeff, WB8NHV Collecting, restoring and enjoying vintage Zenith radios since 2002 Zenith. Gone, but not forgotten.
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#5
03-08-2016, 03:20 PM
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T933! Love em! Most likely a shorted HV rectifier (may be a 3CU3, if memory serves me correct). I have never seen loss of drive on a T933 but have had a number of shorted HV rectifiers.
I have seen (and changed) a number of flybacks in them but I find that if the horizontal current is adjusted properly the flybacks don't give a problem. Always discharge the picture tube anode on this chassis. A shorted 3CU3 may give you a bit of a jolt once you remove the cap and try to remove the tube. It is easy to check drive with the horizontal output removed if you have a VTVM. Just look for high frequency (AC) on the control grid pin of the horizontal output socket. A VTVM is necessary, digital meters get confused when reading this signal. A scope is good but be careful to make sure you are on the right pin. I can bring my schematic tomorrow and give more info. By the way, a T933 is my avatar and a well used daily driver! Oh, if the CRT looks like it is weak once you get HV back, the horizontal blanker tube is the main cause of this!
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#6
03-08-2016, 05:57 PM
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In my years of working on tube type color sets, I have seen many 6JE6s, and other horizontal output tubes, crack along the bottom for no cause at all, other than age. Although I would definitely check the damper, HV rectiifier tube, and horizontal osc tubes for sure as well, as mentioned in the above posts. If the flyback is good, sometimes it's best to change all of those just to be on the safe side, since 6JE6s are are not cheap.
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#8
03-09-2016, 12:55 PM
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#9
03-09-2016, 03:48 PM
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Lol, stupid spell correct. I'm using a pos Samsung galaxy tab 4 and all it ever does is change what I type.
 the 6JE6C in this set was cracked along the bottom.
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#10
03-09-2016, 03:54 PM
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Quote:
Rca 7558 Rca 6GK6 Rca 6GH8A Rca 6GM5 Rca 5763 Rca 12AT7/ECC81 Raytheon 6AW8A GE 6JE6C/6LQ6 GE 6JE6C/6LQ6 GE 6GK6 GE 7061 GE 7061 GE 6BJ6 Sylvania 6BA6 GE 6BJ6 GE 6BJ6 Raytheon 6AW8A GE 12BE6 GE 6JE6C/6LQ6 GE 6BJ6 GE 6BJ6
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