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#1
02-08-2020, 02:07 PM
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Keyed AGC, deal breaker?
I want to restore an early fifties small console TV, and many of them have a couple of design issues that I know little about - I started in the business in the early 70s..
The first is keyed AGC. I've seen a bunch of early 50s TVs that seem to use the contrast control as the AGC. Do these TVs exhibit contrast shifting with picture content or signal strength? Is it annoying? Second, many don't have aluminized CRTs. Again, deal breaker or do non-aluminized tubes have nice pictures on them if they''re strong enough? I actually own three fifties TVs, the first is a GE console with rodent damage over the tuner (bad), and I think it's beyond reasonable hope. The second is an Andrea roundie, and is beautifully built, but it's a table model and I'd prefer a small console. I found a CRT brightener on it but the tube without the brightener checks pretty good... It has a continuously variable tuner and FM radio tuner, but there's a broken phenolic gear on the tuner shaft. Doesn't seem likely to be found anywhere and I'm not a machinist. Both also have 25mhz IFs, and my generators all run higher. The third is a late 50s RCA metal portable that I may restore just for sh*ts and giggles at some point. Any suggestions appreciated. John 
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#2
02-08-2020, 03:43 PM
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2) Where are you going to find a variable analog signal to worry about? You will be feeding these with some local signal source or digital/analog converter, and the signal will be constant. 3) Shifting black level may occur if the video is not DC coupled. Circuits for adding DC restoration to certain sets have been published here. Further edit: do you want the DC coupling or lack of it to be like the original set, or want to fix it? Either philosophy seems to be reasonable to me, but it's definitely a choice. Also note, that the 1940s iconoscopes in cameras were by nature AC coupled, plus had shading issues that could wash a variable fog over some areas of the image and not others. Again, you need to consider if you want to show the set with authentic warts or modern fixes. Last edited by old_tv_nut; 02-08-2020 at 03:52 PM.
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#3
02-08-2020, 06:03 PM
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Aluminization increases CRT brightness and eliminates fiddling with an ion trap. A very strong non-aluminized tube can be brighter than a moderate strength aluminized tube.... Aluminization makes the most difference on tubes that are near dead...an aluminized tube will give a picture with a gun slightly too dead for a non-aluminized CRT. Either will work fine if the gun is strong enough and the chassis is working properly.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
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#4
02-15-2020, 09:07 PM
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I had one of those Andrea sets; someone had glued the tuning knob in place and my efforts to dislodge it destroyed the mechanism. I was able to locate a NOS unit here on VK. That same basic tuner was used by several companies, mostly DuMont, and they do turn up. Lots of caps in that set but very nice build quality.
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Bryan
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#5
02-16-2020, 08:12 AM
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 I have no experience with early 50s TVs, but was struck at how much better built that Andrea is compared to the GE I have, and they're both 1951 models. The broken gear appears to have been factory peened to the outer knob shaft, so it looks like a DuMont tuning knob won't work unless I can cut/fit the Andrea outer knob to the Muntz shaft. Thanks for the info. John
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#6
02-16-2020, 06:36 PM
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Phil Nelson
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#7
02-16-2020, 06:54 PM
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This has a metal cone tube which I'm led to believe is not a high probability shot to be good. To make things worse, I found it with a CRT brightener on it. When I check the tube, it checks strong after a few minutes, so I'm hoping that as the high voltage dropped because of the failing 10KV caps I found, some ham 'n egger threw a brightener on it - hopefully not being run that long or at all with it. Maybe they tried the brightener then abandoned it. In any case, I won't spend a lot of time on it. I already restuffed a 40-40 @ 500-500 and changed the dead 5U4 and one 1B3. I'll add the HV caps and see if she'll run. If the tube is strong and the flyback good, I'll go ahead and do a full restore and alignment. These were supposed to be very good performers. It certainly is well built. I've had it about 25 years along with a bunch of other stuff I had to take as a package deal to get what I wanted (some Fisher tube HiFi stuff). For some insane reason, I decided a nice 50s B&W TV would look nice in our front room where my wife and I have a 1929 RCA Radiola console and an 1857 reed organ along with a turn of the century Waterbury gingerbread clock from her family. TMI? LOL.  John
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#8
02-17-2020, 08:13 PM
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Does it look like this one?
 I'm a fan of the early DuMont sets that use an Inputuner and provide integrated FM radio. Not many companies did that. Am I right in guessing this is an original Andrea design, rather than a DuMont clone? That would make it somewhat unusual, at least in my book. With a 16" CRT, that must be one hefty tabletop! Phil Nelson Phil's Old Radios https://antiqueradio.org/index.html
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#9
02-17-2020, 08:29 PM
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That's the one. I'm not familiar with DuMont at all (or any 50s TVs to be fair) so I don't know if it's an Andrea design or not. It is indeed fairly stout, and the chassis takes up all the cabinet space. The GE console I have has a chassis much smaller than this Andrea has. John
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