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#31
06-28-2015, 11:35 PM
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Very nice work.
__________________
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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#32
06-30-2015, 09:35 PM
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That may be true, but sometimes it is good to be weird.
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#33
07-04-2015, 06:20 PM
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Today I recapped the TV power supply. Since I am not restuffing electrolytics,
just papers, this was easy. It worked correctly with no load. But I noticed something odd in the CRT resistor chain: The lowest resistor in the chain is shown on all schematics as 330K. Mine is 560K. The schematic shows the CRT "screen" connected at the top of of the 330K resistor, giving 250V. My power supply has it attached 470K above the 560K resistor, or 1030K above ground. All other resistors are as specified. This makes the voltage about 780, which is what I measure. This is not original. Despite being in crates, my chassis have clearly been well used an the PS has been worked on a bit. The original connection was clearly just cut off. What was going on? Last edited by dtvmcdonald; 07-04-2015 at 06:26 PM.
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#34
07-04-2015, 07:11 PM
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There are four different schematics for the TRK12/120. You need to check them all and see which one your chassis' matches best. They can all be found in the RCA Red books.
Darryl
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#35
07-04-2015, 08:04 PM
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I have the original RCA manual and the Rider's.
The TV main chassis is for sure a TRK12 because it has no limiter tube. It has no grid cap on tube 9, no connections to pins 3 and 4, so it must be the version in Rider's that uses IF grid bias as contrast control. There used to be connections to pins 1, 3, and 4, but no longer, they were cut off. Of course, I am going to use one of the radar tubes rather than a real 12AP4 so that may make a difference in the G2 CRT bias. Steve McVoy: do you know if the 12LP4 also needs different grid bias, or is it non-critical for test use?
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#36
07-05-2015, 01:01 PM
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Question: the video chassis has 2 multitap chassis mount resistors that work
like Candohms but are not. They are constructed differently and look more modern. If their resistance is OK, is it reasonable to just leave them as-is?
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#37
07-05-2015, 02:05 PM
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If they show the proper resistance and aren't shorted to the chassis, keep them.
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#38
07-11-2015, 07:31 AM
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I need to know two things to proceed on this TV:
Are the black (or dark gray) black plastic lozenge shaped capacitors (150 to 3300 pF) in the TRK12 paper or mica, that is, should I replace them on preventative grounds? I have proper mica replacements. Secondly, what pins are what on the replacement radar CRT I have? I have all the caps except those, the .005 uF paper ones, and the 0.1 uF 300V one replaced. When those parts arrive, today or Monday from Mouser, and I replace them, (about 40 .005 ones!) I will be ready to try it without the CRT and HV. I have replaced only one resistor, the 13k part of the pseudo-Candohm. All others were only borderline 20% high or spot on ... nothing in between! And very remarkably indeed, ALL resistors of the same value and type were within +2% of each other!
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#39
07-11-2015, 07:35 AM
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I'll check the pins on the CRT when I get back to Ohio in a couple of weeks.
I wouldn't replace the low value caps unless they are bad.
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#40
07-11-2015, 11:59 PM
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I've completed recapping.
I removed the fuse from the CRT HV supply. With no tubes except the B+ rectifier inserted I brought it up on a Variac with a meter on the B+. It got up to normal voltage with not fuss. I then inserted all tubes except the horiz and vertical outputs. Or rather, I tied to. It seems I ordered the tubes for a TRK-120 and I've got a TRK-12. I'm missing a 6F8G and a 6H6. However both of these, despite what the specs say, are being used as single diodes. They were temporarily bridged with (hold nose) silicon. Again bringing up on the Variac caused no fuss. Did I mention I was feeding a signal in? I checked the oscillator frequencies and they are set for modern channels 2-6 as a rubber stamp on the chassis says. It was set to Ch. 2. Checking the signal path with a scope showed that it was getting all the way to the outputs (audio and video). Fine tuning and contrast (actually grid bias on all IF stages) wore as expected. The video waveform actually looks rather passable. The sound sounds OK on 2000 ohm phones (remember that it has no amplifier.) Next I checked the sync separator chain and it works fine. The horizontal osc works and the hold works but the pullin range is rather small. Is this normal for TRK 12s? No sweep was getting to the horizontal output grid (no tube, remember). This was traced to a bad width pot. Turning it caused drive to appear, and disappear, with loud pops from arcing inside it. I have a modern one that should work if it can take 300 volts. The vertical system worked correctly, but again with rather small pullin range. The B+ for the 2nd sync separator is 7 volts [sic] as shown on the schematic. So much for today!
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#41
07-12-2015, 01:37 AM
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Gradually it is returning to life!
__________________
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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#42
07-12-2015, 12:45 PM
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I was wrong about the oscillator frequencies, it was
nearing midnight and I was blindly comparing to the channel limits printed on the set, not modern ones. They are still the 1941 set, i.e. the set with one channel at 50-56 MHz. This means only channels 3 and 4 work with modern signals. There is no "major" oscillator adjustment in the set, so I'm leaving it as-is. The problem pot was taken apart and examined. I could find nothing wrong with it, so cleaned it up, used deOxit on it and added a Mylar film insulation layer between the terminals and the case front, which was uninsulated and rather a close gap. It now works fine. This was a really high-class part in its day. A photo of the chassis at present is attached. The big blue 13K power resistor is obvious. There are numerous Nichicon radial electrolytics scattered around .. some are invisible in the photo. Only one small resistor was replaced, with a modern 1/2 watt carbon one (the one meg one). Other ones of that sort were original. There are two unrestuffed .005 uF caps, due to worries about installation damage if restuffed. There are also of course the two silicon diodes across the two missing tubes. I now have to await word on what the radar CRT connects are, make a protective box for the 7.5 kV rectifier, and make an HV connector adapter. It also needs a small dropping resistor, only 5 to7 volts..
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#44
07-13-2015, 09:09 AM
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Quote:
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#45
07-13-2015, 03:33 PM
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Oh yes, one more question.
I took the radar tube out of its box and examined it. I was told that it had an outer Aquadag coating, forming the filter cap usual on later TV CRTs. I notice no such coating. The front 2/3 of the bell insides is aluminum coated, the back 1/3 and a couple of inches back into the neck is Aquadag coated on the inside ... but no Aquadag on the outside. I even tried scratching a bit off at the edge with my fingernail, nothing came off. If you've used one of these, was it outside coated?
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