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#76
05-22-2012, 01:50 PM
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I'm with Bob when it comes to the 15G. If you have one with good emissions and getters, it's probably best to leave it alone. After all, it held vacuum for the last 58 years without any help so why fix what isn't broken. If on the other hand you need a rebuild, the full protocal of leak sealing ought to be applied whether it was still under vacuum or not. As proven by the rebuild attempt of John's under vacuum tube, leaks can pop up even if you assume the thing was good before. It still took a full 30 days for John's tube to become gassy, so it may start out good and deteriorate. I think in the future, 15G owners will likely opt to have the tube treated with frit regardless if it was still under vacuum or not.
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Evolution... 
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#77
05-23-2012, 06:58 PM
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Power up!
Chuck A was up over the weekend, so we decided to give the Crosley a try. Saturday evening we swapped out the dud 30BP4 for the spare I had. After a lot of adjusting and hooking things up, we connected the variac and brought it up. Nice aucio, but that was all. No high voltage. Kind of a let down. We called it quits for the evening.
Next morning we put the 2 chassis, yoke/focus coil assembly and speaker on the work bench and hooked it all up. First discovery was a blown fuse (which I had tested good earlier). We replaced it and began looking for high voltage. But here is where I made a really stupid error. Using my B&K HV probe which is a 1000:1 divider, I misread the meter. It was showing voltages (at various times) between 1.1 and 2.0 volts. I was calling this 11K - 20K volts, and we spent the whole day trying to figure out why the high voltage was low and unstable. It would go from 15-16KV down to 11KV or less as thing warmed up. Swapping tubes, checking wiring, freeze spray, nothing we tried was any use. Chuck A departed back down to south Florida in the morning. Later that afternoon I sat down to have another go at it. Apparently my brain was actually working, and I realized that the meter had been telling us that there was ONLY 1.1-2.0 KV! And yet, using a screwdriver, one could get a big purple arc from the plate of the first 1B3 in the HV doubler. I immediately realized that this meant the rectifiers were not working, probably because the filaments were not being lit. The tubes derrive their filament voltage from the sweep flyback, not the HV flyback. I put two solid state 1B3 replacements in and go 28KV. Hooray! A check of the bias on the two 6BG6s driving the sweep flyback revealed no screen grid bias. The 3K ohm 10W bias resistor (which had ohmed as good earlier) was open. With a replacement installed and the 1B3s back in, I got a robust 20KV. After things warmed up, it settled at 18KV plus. I tested all the tubes on the TV chassis, and found none to be bad. I reinstalled everything back in the cabinet, and after some adjusting of the yoke and focus coil and centering lever, gat a very presentable picture. I actually looks much better than these photos indicate. This CRT works even better than I hoped. Plenty of brightness and contrast. Next time Chuck A is up, we will do setup on the V&H size and lin, and play with the pincushion magnets. 
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John Folsom
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#79
05-23-2012, 07:53 PM
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Thats one handsome TV set! I've never seen a round screen 30 incher!
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#81
05-23-2012, 08:02 PM
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Wow, that is an extremely impressive set! Way to go!
Dave
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#82
05-24-2012, 12:55 AM
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Ditto I'm impressed.
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#83
05-24-2012, 06:45 AM
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Kinda sad, really...How many of those Dumont/Crosley sets are still around after 60 yrs, & how many still WORK ? And now that Scotty/Hawkeye has thrown in the towel, there will likely NEVER be anymore ever rescued...Says something pretty damning, to me, anyway, that w/all our grand & glorious 2012 technology, we CAN'T bring an obsolete television back to life....Well, except for a small group of Mad Monks, maybe....(grin)
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Benevolent Despot
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#84
05-24-2012, 01:56 PM
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That looks great, John.
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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."
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#85
05-24-2012, 06:22 PM
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Quote:
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#86
05-24-2012, 07:05 PM
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I am aware of at least 2 or 3 working DuMont 30" sets (I have one), and there are probably a few more. The ETF website shows 8 sets known, not sure how many are working.
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John Folsom
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#88
05-24-2012, 09:37 PM
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My friends uncle owned a TV shop that closed in the 90's. he has one of those 30" CRT's at his house. if I ever get over there, I might try to buy it in case someone here needs one.
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"It's a mad mad mad mad world" !! http://www.youtube.com/user/mwstaton64?feature=mhee
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#89
05-24-2012, 11:03 PM
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Very nice, John! And, you only had to take it apart twice!!
  Seriously, nice job on a very nice set. I saw the set in your garage when I came. I fell in love with it then.... Bill Cahill
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"Tubes are those little glass things that light up orange unless there is a short.. Then they light up all pretty colors..." Please join my forum. http://www.tuberadioforum.com/
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#90
05-25-2012, 04:56 PM
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Quote:
Cliff
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Linear Mode
