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  #16  
Old 02-03-2010, 06:50 PM
ctc17 ctc17 is offline
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Update...
One lead to the degaussing coil was loose and hanging. Got that hooked up and worked on setting up the convergence and purity for awhile.
Got a fair bw picture. I do get some kind of color, mostly a yellow green if I turn the color all the way up and mess with the fine tuning.
Got caps and a color crystal today, will pull the chassis and replace on Saturday.

I got this set setup in a 2 bedroom house we have for rent. When perspective tenants come to look the set will be playing in the living room. I have been using the stereo along with my satellite radio while we are working on the house. Escape is the perfect channel for this vintage of combo
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  #17  
Old 02-03-2010, 10:36 PM
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Don't forget to try the 6GH8's first - they'll check fine on a tube tester, but fail as a color burst amp/oscillator. We used to use those RCA's to actually test used 6GH8's - if it worked in an RCA color circuit, it was considered good.

Their use in color circuits was probably a stretch - they were originially designed as horizontal oscillator tubes. There's a big difference in 15,750 Hz and 3.575945 MHZ!

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  #18  
Old 02-04-2010, 11:12 AM
peverett peverett is offline
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Color TVs were not the first time manufacterers tried to stretch a tubes design characteristics. There are many early AM/FM radios that use a 12BE6 for both bands. The better ones used a 12AT7, etc.
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  #19  
Old 02-04-2010, 01:03 PM
ctc17 ctc17 is offline
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update2

Tested and replaced all bad electrolytes. I changed the crystal anyway because I got a new one here and I had the chassis out. Now I get the rainbow that rolls up and a nice solid bw picture. Will test the tubes next. I know im going about this kinda backwards..
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  #20  
Old 02-04-2010, 01:18 PM
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Charlie Charlie is offline
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Quote:
Originally Posted by Findm-Keepm View Post
Their use in color circuits was probably a stretch - they were originially designed as horizontal oscillator tubes. There's a big difference in 15,750 Hz and 3.575945 MHZ!
I've wondered if 6GH8's were used for anything other than color circuits. Don't recall off hand if I've seen them in sets doing other jobs. My "used tube" buckets always have a lot of them in there.

I attempted getting my color to lock in on my 15 years ago by replacing the 6GH8... must have gone thru 3 or 4 before finding one that finally worked... and they were all NIB tubes.
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  #21  
Old 02-04-2010, 02:34 PM
peverett peverett is offline
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I have seen GE B&W sets that used 6GH8s as horizontal oscillators. Zenith may have also used these as horizontal oscillators.
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  #22  
Old 02-04-2010, 02:44 PM
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I've seen them used in place of a 6EA8 in Zenith tuners before too. Had a roundie with one in the tuner. It worked fine.
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  #23  
Old 02-04-2010, 02:45 PM
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Quote:
Originally Posted by peverett View Post
I have seen GE B&W sets that used 6GH8s as horizontal oscillators. Zenith may have also used these as horizontal oscillators.
I think Zenith did use them in some of the 70's B/W hybrids for a horizontal oscillator IIRC.
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  #24  
Old 02-04-2010, 10:12 PM
ctc17 ctc17 is offline
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Got color. I switched the two 6gh8 and color came in. I tested them too, even cut the filament voltage back to 4.5 and they tested good. No leakage, no shorts. They both tested good...guess its just that sensitive.

Had to adjust the sound coils because of buzzing. Ok picture but noisy. Like a weak signal. I bet the set needs a full alignment if the sound coils are any indication.

Anyone here ever done a total if/rf alignment successfully?
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  #25  
Old 02-04-2010, 10:51 PM
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Quote:
Originally Posted by Charlie View Post
I attempted getting my color to lock in on my 15 years ago by replacing the 6GH8... must have gone thru 3 or 4 before finding one that finally worked... and they were all NIB tubes.
'tain't just tubes that have personality conflicts - on of my laptops suddenly died. I popped out one of the memory cards and it worked just fine. In fact it worked with either, but not both. Had to replace them (they were the originals) to get the computer to work as it should.

If you think 6GH8's are bad, the 5GH8 was no better - and between RCA and Westinghouse/Penny's sets, there were plenty. I've seen many a RCA 19" color set fixed by just moving 5GH8's around between the sync/color/horiz circuits in the set.

When I worked at an electronics distributor in the early 80's - we sold 6GH8's by the sleeve of 5 - not because the shop needed to replace that many, but because they need that many to replace one - Charlie, it seems, you too!
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  #26  
Old 02-04-2010, 11:02 PM
DaveWM DaveWM is offline
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I would check the RF tuner tube 1st as well as some new IF tubes before going anywhere near an alignment.
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  #27  
Old 02-04-2010, 11:21 PM
ctc17 ctc17 is offline
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I just had a lapse of sanity and bought this. What do I need besides this (if will even work for tv alignment) ?

I really want to be able to do good alignments on my old sets and have them come out right. I checked all the tubes and even subbed most all of them. The sound was so far off the video has to be off to.
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  #28  
Old 02-05-2010, 07:43 AM
DaveWM DaveWM is offline
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yea I hear ya, alignment just leaves a bit of a sour taste in my mouth.

I decided to mess with IF alignmnent on my last B&W. Of course I had no equipment so I attempted to do it by ear and eye ()... anyway the plan was just to turn each lug just a bit and keep up with what I had done. That plan fell apart pretty quick, then one of the coil forms broke apart....

I ended up making a new form thread so the slug would tune. Then I got a B&k 415 sweep gen with markers (very nice). I started by confirming the marker freq with a freq counter. Lots of hookup cables and trial and error attempts I was finally able to get the right shape and markers in the right place.

I think it just take a lot of practice to get it right, and to know when ot stop.

The Biggest problem I think it the fragile cores, that being said I completely understand your wanting to do it

You just want to be absolultly sure its really the problem. Of course the best way to know that is to get your equipment working properly and then go ahead and sweeep the circuits, if the bandpass looks right then dont touch a thing, least something breaks and set you back, 1st do no harm.

In the end my B&W problem turned out to be a keyed agc with an open cap letting horz freq pulses get thru. The agc voltage was correct per the DMM but when you looked at the scope you could see it plain as day.

For your marker gen I would suggest you get a freq counter and check it out.

Last edited by DaveWM; 02-05-2010 at 07:50 AM.
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  #29  
Old 02-05-2010, 10:27 AM
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Last edited by andy; 12-07-2021 at 01:37 PM.
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  #30  
Old 02-05-2010, 11:17 AM
DaveWM DaveWM is offline
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on thing I learned is the test equipment itself can mess up the curve. I had an ill shaped hump, turned out to be the clip on the TP was close the the IF coil, it made a HUGE diff just moving that clip around. Tubes effect it as well. One time it turned out to be an intermittant IF coil connection (prob due to all my fiddling). Considering the RF freq are so much higher than the IF, there is no way I would get near the tuner for alingment, not really needed anymore do the the lack of OTA analog signals, most of my watching is on channel 2 or 3 whcih ever works better.

I really wanted to do an IF alignment just to see how it works and I like to learn new stuff, from that exp I learned to respect IF aliignment but not fear it. Still I would only do if if all else checked ok AND the sweep proved a problem as is AND I was pretty darn sure I had the hookups right.

What I found very helpful was to hook up to another chassis (hopefully the same model) that is working well and sweep that. That a good way to validate the hookup and how it should look. What I found was while the waveforms were sorta like they should be, they were by no means perfect looking yet the picture was fine.

From this I deduce, the IF curve was not as critical as I thought (at least on a B&W set) or my connections were impacting the curve. I suspect the latter since minor repositioning woudl alter the results. I tried to get the wave as near as possible on the working set, noted the cable setups, then returned to the non working set (after I goofed it up) did the exact same deal with lots of care on lead dress, and then lots of patiencd on AGC bias and RF power to get the hump to not clip. I ended up with less gain but better looking bandwidth. The result was a near perfect pic that look pretty much the same as a direct feed of the composite signal at the post detector TP.

Which brings up a second point, I would recommend you do a composite video feed directly at that TP. that would isolate the issue to before or after the IF section.
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