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#17
03-15-2011, 07:41 PM
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hi andy,
I want to do this to my RCA 8PT... I was looking at the 630 schematic and it does look like just a diode, but that set drives the grid of the crt and is very different to my 8pt Can you provide a bit more specific info about how to do this? It would be much appreciated. 
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#20
03-16-2011, 12:17 PM
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i don't remember the 60's zenith sets i watched do this with the blacks , they had blacks and black at fade out , i know this 61 motorola i have that was part of a tv sales/repair that never sold does this , night scenes are very gray, i don't seem to remeber the rca 8-t-241 do it but its been a while since i've run it
mike
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#21
03-20-2011, 08:20 PM
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When I had my Magnavox CT-246 16" tv/radio/phono console working briefly in 1980-81, I remember how nice it was to have DC restoration on a B&W TV.
__________________
Chris Quote from another forum: "(Antique TV collecting) always seemed to me to be a fringe hobby that only weirdos did."
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#23
04-26-2011, 03:26 PM
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Truetone 2D1091
Took me a bit to find my schematic of my Truetone. I would give this set high marks. 4 video IF's, dc restoration, dual chokes in the B+ supply (no focus coil as a choke, two actual chokes)! A rather interesting AGC circuit and a tuner that is absolutely bizarre. It even has a spot killer for the CRT on turn-off! Intercarrier IF.
Mine is in poor condition (mice!) so it may end up a "Frankenset". The tuner is more than a "basketcase" and without analog, it may be fun to set it up for composite video. The only thing I see it lacking would be a limiter in the audio circuit. And the original CRT is good!
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#24
04-26-2011, 04:11 PM
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Quote:
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#25
04-27-2011, 10:02 PM
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Can this be used on other sets?
I've always lamented the lack of DC resto in my Emerson 1224 (which, for some reason, seems especially bad among old B&W sets - any significant white in the picture, and anything else in the picture turns to solid black), and am dying to try it on my set.
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#26
04-29-2011, 10:49 AM
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Zenith made a line of top-of-the-line chassis' in the late 1950 through 1963 that had switchable DC restoration from the front of the set. They called it "dynamic contrast" or "dynamic picture" as I remember it. It was a push-pull switch on the back of one of the picture controls under the screen.
Those same sets, while having only 3 IF stages, also used a new tube at the time. The 6EJ/EH7 was capable of much higher gain that previously used tubes, so they had wideband IFs with gain. These were 21" and/or 23" sets. I've worked on a few when I worked in a service shop, and my great grandmother had one. I've never seen a better picture on a B/W TV set. In fact, I'd say those particular Zenith chassis were THE BEST monochrome chassis ever made, hands down, over and above ANY other manufacturer. One other cool set I know of with DC restoration was the first Magnavox solid state or "astrosonic" large screen TV chassis. Introduced in 1965, it has DC coupled video amp stages, and most came with a 24" or 27" inch CRT. We had a stereo theatre in danish modern with this TV chassis, and the common astrosonic radio chassis of the day and a micromatic changer. It seemed to play forever with very little trouble, and still worked well when I got our first color set. I'd like to find one of those, but I've never seen another since the one my family had. I don't think they sold many as those with the money for a combo like that prolly went for color. just my $.02.
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#27
04-29-2011, 12:17 PM
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I can vouch for everything TV Engineer wrote. I had a 1963 Zenith 23" console which produced probably the best picture I ever saw on a b&w set. It had three IF stages, two 6EH7s and a 6EJ7, but no dynamic picture control, though it did have a "peak picture" control on the front panel, behind the drop-down secondary-control door below the CRT. The audio was great as well, owing to the set's 6x9 speaker and 6BN6/6BQ5 audio stage. They don't make them like that anymore.
__________________
Jeff, WB8NHV Collecting, restoring and enjoying vintage Zenith radios since 2002 Zenith. Gone, but not forgotten.
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#29
04-30-2011, 08:55 PM
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Black-and-white CCTV monitors often have DC restoration, and one model I know of has a switch for it on the back panel. These are 9" and 12" monitors though; the biggest I have seen for sale in recent years was a 20" version.
__________________
Chris Quote from another forum: "(Antique TV collecting) always seemed to me to be a fringe hobby that only weirdos did."
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