#136
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That puppy was kickin' our collective keester for sure. Glad you finally nailed it to the wall.
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#137
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The candohms I have taken apart were insulated with paper.
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#138
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Still not enough contrast to the picture though. This thing should have amazing contrast, and it's too washed out for what I know this set should be doing.
Gonna have to yank the chassis for the 53rd time and start testing the resistors in the AGC. The contrast control is questionable too, as it has a dead spot and seems to not do a heck of a lot.
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"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
#139
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Well, in lookin' at the schematic, the contrast control appears to be a manual (not automatic) gain control, varying the negative grid bias on the IF tubes. Low gain would indicate the control voltage is too negative.
The control pot is supplied with a negative voltage thru R44 (2.7K), and the other end of the pot goes to ground thru R42 (680 ohms). The control voltage being too high could be due to: R44 being too low in value, or R42 being too high in value. Those would be the first things I would check. Then disconnect one end of the pot, and connect an ohmmeter to that end and to the wiper. Rotate the control, looking for dead spots. Also be sure the control element (10K) is not open. Then go ahead and check R40, R41, and R43 (whose purpose appears to be to make the control's action more linear). |
#140
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On my 8TS30, the contrast control has a wide range of action, from no video to way overloaded. It is indeed a "manual (IF) gain control"; there is no AGC.
Compare to your DeWald BT-100, how does that set's contrast control behave? Both sets should be nearly the same, I would expect.
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Chris Quote from another forum: "(Antique TV collecting) always seemed to me to be a fringe hobby that only weirdos did." |
Audiokarma |
#141
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Well yeah.....I interchange the terms "contrast" and "AGC" on this set because they're one in the same.
It's definiitely washed out and has very little range.....from totally washed out to barely adequate. Plus, there's a dead spot on the control. The DeWald is the same as your 8TS30, which is the same as my 8TS30 (this isn't even my set!), so I know there's definitely something awry.
__________________
"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
#142
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Gonna finally call this one done after I give the tuner a good cleaning
The screen shot is lousy, but the set regained contrast after I removed ALL the wires from the candohm, and used terminal strips to isolate everything. It looks like a bit of a train wreck, but hey, it works! It's not *as* contrast-y as my 8TS30, but this set has zero horizontal or vertical lock drift....and mine does a little while it's warming up. I'll just chalk that up to their individual "personalities"
__________________
"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
#143
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Well here's an ironic post-script to this thread!!!
I bought a restored 8TS30 at the ETF auction, and I remembered that I did the work to it, but it JUST dawned on me that it was THIS SET!! There it is, under the table: https://www.flickr.com/photos/420028...7668760424818/ The contrast issue ended up being a couple micas, it now works as good as new. And now it's back here!!!
__________________
"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
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