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#61
04-03-2010, 11:35 AM
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Nope...it was that darn 330k resistor. I went back and tested it, only to find that it would suddenly read at 400k, then 300k, then open. I pulled it out of circuit, and it read as an open. So, now I have excellent vertical lock, but still somewhat iffy horizontal lock with that weird blanking bar bleed. I'll photograph what I mean (hopefully) later today.
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#62
04-03-2010, 08:10 PM
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Okay, I am now focusing more on the horizontal section, as there seems to be poor regulation there. The raster has a bit of a wavy motion to it, and I am getting a black smear coming in from the left side of the screen (it is present in the distorted picture I took a few posts back). Looking at the clipper/sync amp tube (v16) all voltages check out now that that vertical issue has been corrected. Now moving onto the horizontal discriminator tube, I have low plate voltage for v17a-about -6 volts with no video input and -12vDC with signal input. It should be -95vDC. V18a and V17b's voltages check out fine. What has me puzzled is where does this -95vdc come from? Following the schematic, I don't see a plate supply voltage running to this one.
A bit of good news is that the vertical lock is SOLID. Rotating the vert. hold control will make the picture a little jumpy at the extremes, but no rolling. This is a pretty solid circuit now.
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#63
04-03-2010, 08:34 PM
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Maybe C48 is open?
The grids are tied to the plates so the 6SL7s are acting like diodes. I'm not sure of the level of the output of the horizontal sync amp but it'll be rectifying that signal and the feedback from the flyback. John
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#64
04-03-2010, 09:36 PM
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I just picked up one of these sets too
 I'm not going to be working on it anytime soon, but I can take some detailed pictures if you'd like to compare it to yours.
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#65
04-03-2010, 10:57 PM
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According to my docs, the correct plate voltage for V17A is -6.4 v.
Here's a scan My set has a 6AL5 too. Last edited by bandersen; 04-03-2010 at 11:27 PM.
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| Audiokarma |
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#67
04-03-2010, 11:27 PM
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Quote:
That's right - this set has channel 1 
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#68
04-03-2010, 11:52 PM
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Quote:
John
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#69
04-06-2010, 08:18 PM
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Well, I'd chalk that up to a misprint. Especially after tonight when I saw that I am supposed to have 345v on pin 2 of the 6bg6. I'm not an expert, but I do believe that would blow out the tube's 6v rated filament. From the schematic, my plate voltages on the 6sn7 would appear about 20% low, but without some reasonable documentation, that will be difficult. Could anyone provide me with the proper voltages for the tubes in the horizontal section?
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#70
04-06-2010, 08:57 PM
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Checkout post #65 in this thread
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| Audiokarma |
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#71
04-06-2010, 09:28 PM
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Woah! Now that is quite different from my numbers! Your info is telling me that I am off by about 100v on my 6sn7 plates (v21 a&b). Guess I better replace those plate resistors to get that back in line...
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#72
04-06-2010, 10:08 PM
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Here is a screenshot of where I am at right now. The picture doesn't roll or anything like that, just a bad video picture and some pretty bad flag-waving of the raster.
GEDC0172.jpg
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#73
04-06-2010, 11:36 PM
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Weird. I downloaded the GE 803 Rider's courtesy of the ETF. http://www.earlytelevision.org/tv_sc..._diagrams.html
It's pretty darn close to the 802 and it has loads of waveform measurments in addition to the socket voltage chart. Maybe you can use a scope to check your waveforms ?
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#74
04-17-2010, 10:09 PM
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You're right in that the 803 schematic is a close match. In fact, a lot of, if not all of the component numbers match up to my 802 schematic.
I spent another day hammering away at this thing. Primarily I was fooling around with that awful video noise producing that black blob of static on the edge of the screen. My scope traced the issue right back to the video input, and after tacking down another bad ground, I had a cleaner picture. I also fooled around with v21's plate voltages, which should be about 230 and 245vDC. My set was only around 130 and 145 volts. I had to change the plate resistors quite a few times to up the voltage enough to this "stock" setting. It provided no difference in Horiz. lock, and only seemed to introduce some drive lines, so I went back to the lower voltage. The plate resistors (100 and 150k) seemed to be original, and were within 5% of their values. The 801 has lower plate voltages like mine...so mine is probably running properly. The waveforms are certainly clean. I corrected a blooming issue by replacing a 470k resistor hidden inside of the 1B3's base (the 1B3 is mounted on 3 ceramic standoffs, the wiring in the base covered with a metal shroud). So here we are: GEDC0182.jpg GEDC0181.jpg I can now use the 6al5 properly, so DC resto is working pretty well. Retrace lines are visible, but I wouldn't be surprised if this set lacks vertical blanking. The picture still has a bit of waving to it, but it is extremely slight. I included the second picture, as it illustrates the only other issue I have with the picture-those faint vertical bars off to the left side. But, it's nice to have a watchable picture on this set.
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Linear Mode
