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  #46  
Old 12-11-2018, 07:45 AM
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Yep you've got that right! When I did my 25" Motorola colour tv, I marked the worm gear on the band before I took it apart, and it was much tighter than I would have expected glass to take.

This one is more of a strap holding it down, than a band like newer TVs have. It rests on two mounting points, and the strap goes only on the top and sides. I wish Marconi gave me a torque spec in inch pounds, for the retaining screws. I think it's good now, though.

On another topic, I need to find some tubes for the tuner. I sure can't complain about the price of tubes for this TV, the only semi expensive one is the horizontal output, and I have a few of those in my misc. Junk.
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  #47  
Old 12-13-2018, 11:20 AM
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Kevin Kuehn Kevin Kuehn is offline
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I find it interesting how thick the insulating donut is on that flyback HV winding, and the thick strain relief where the anode lead exits is actually functional. Compared to most of our American built flybacks that one looks very robust. It irritates me how so many NOS flys have a crack right where the anode lead leaves the HV winding. Max, do you know what year your set was made?

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  #48  
Old 12-26-2018, 06:45 PM
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Quote:
Originally Posted by Kevin Kuehn View Post
I find it interesting how thick the insulating donut is on that flyback HV winding, and the thick strain relief where the anode lead exits is actually functional. Compared to most of our American built flybacks that one looks very robust. It irritates me how so many NOS flys have a crack right where the anode lead leaves the HV winding. Max, do you know what year your set was made?

Most of the parts have a 1958 date code, so I believe 1958 or maybe 1959.
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  #49  
Old 03-17-2020, 02:33 PM
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Back to this TV after some time, I wanted something to watch the news on while I'm dealing with the COVID quarantine. I turned it on, and now horizontal refuses to lock properly, and the image looks inverted. Hopefully the better techs here will know what this means by looking at the image. Would appreciate any suggestions. Last time I tried the TV it did show a picture properly.
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  #50  
Old 03-17-2020, 02:40 PM
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Try turning down the AGC control....If AGC is set too high you will loose sync, get negative video, and sometimes sound issues.
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  #51  
Old 03-17-2020, 02:56 PM
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I started it up cold and it synched fine, but then went out of synch again. This chassis does not have an AGC control, surprisingly, although that idea makes a lot of sense.
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  #52  
Old 03-17-2020, 03:06 PM
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Tom, you nailed it - a new 3AL5 AGC detector was the cure, it works properly now.
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  #53  
Old 03-17-2020, 03:36 PM
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Another issue it seems to have is weak sound. Low volume, and quite a bit of buzz in the audio. The picture looks great now.
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  #54  
Old 03-17-2020, 03:36 PM
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Happy to help.
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  #55  
Old 03-17-2020, 03:40 PM
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Originally Posted by maxhifi View Post
Another issue it seems to have is weak sound. Low volume, and quite a bit of buzz in the audio. The picture looks great now.
Does it use a 6BN6 or series string equivalent? If so the buzz control is the first thing to adjust... Assuming fine tuning knob adjustment can't improve the sound.
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  #56  
Old 03-17-2020, 03:46 PM
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Here is the tube layout for the set

I already tried a new 3AL5, and a new 3AU6. I do not have handy a 5U8 to try
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  #57  
Old 03-17-2020, 04:08 PM
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Do you have a tube tester or a strong 6U8? Has the low voltage lytic on the detector been replaced in recent years?

Another option if you don't have a tester is to check voltages on the tube if the grid is normal or less negative (/more positive) but the plate is higher than normal that indicates a weak tube (DC plate current below normal).

There's also the lazy audiophool method of turn the set down, plug the audio output of your video source into your stereo and turn the stereo up....I tend to favor this even on sets with good sound.
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  #58  
Old 03-17-2020, 05:00 PM
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Set was totally recapped in 2018, but project was put on hold so could be an issue there. Suppose could try a 6GH8 for kicks, have no 5U8. Set is series string, so wouldn't be safe to add an input the 3AV6 is weak, and the pentode section of the 5U8 checks okay. Plenty loud with no signal, but barely anything with either a VCR or modulator.

I will check all the voltages in the sound section to be sure. The plate voltages seem okay.
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  #59  
Old 03-17-2020, 05:30 PM
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You get two points today.. a 6GH8 cast off from my CTC38 revived the audio, it is loud and strong now. Will have to find a new 5U8. Thanks again!! This strikes me as odd, because the 5U8 tests only slightly weak on my TV7. For all it will cost I'm thinking to maybe just order a set of new tubes for this TV, it seems like a lot of them are marginal. Interestingly, this set has mostly original tubes, but the 5U8 has been changed already, which indicates to me it might be run hard.
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  #60  
Old 03-17-2020, 07:31 PM
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Hey Max, I have lots of NOS 5U8 tubes.

Gregb
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