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59 RCA Color set (AGC)
1/4/2008 9:40:33 PMchip
HI: And thanks for all your past help. Without a scope how can I tell if my AGC pot is in the correct place,also having trouble getting the purity rings set in the right place. thanks chip
1/5/2008 6:18:18 PMThomas Dermody
You can usually get a fair idea by the picture. Illumination and picture quality should be somewhat uniform for most local stations (other than the necessity for rotating the antenna, adjusting the fine tuning, etc.). If AGC is too strong (AGC signal is reducing the gain of the RF circuitry too heavily), picture will lack contrast. Sync circuits and color circuits may have trouble operating properly due to not receiving a good amount of their signals. On the other hand, if the AGC control is adjusted to that not enough signal reaches the RF circuitry, the RF circuitry may overload for some or all local stations. Contrast might be very heavy. The picture will distort. Sync circuits may have trouble with this condition as well, due to distorted signals (RF overloading--too much gain).

T.

1/6/2008 4:42:07 PMchip
:You can usually get a fair idea by the picture. Illumination and picture quality should be somewhat uniform for most local stations (other than the necessity for rotating the antenna, adjusting the fine tuning, etc.). If AGC is too strong (AGC signal is reducing the gain of the RF circuitry too heavily), picture will lack contrast. Sync circuits and color circuits may have trouble operating properly due to not receiving a good amount of their signals. On the other hand, if the AGC control is adjusted to that not enough signal reaches the RF circuitry, the RF circuitry may overload for some or all local stations. Contrast might be very heavy. The picture will distort. Sync circuits may have trouble with this condition as well, due to distorted signals (RF overloading--too much gain).
:
Thanks : Because of a weak picture tube, The picture has good color and contrast when the AGC is at a low level (need a boost or rebuild, maybe)too much brightness the picture blooms and contrast has to be more than 2/3. Figures and people look ok up close but backgrounds are out of focus.
1/6/2008 11:41:53 PMThomas Dermody
Be sure that it is the picture tube. Have you tested the high voltage rectifier? It can be weak. On my emissions tester, with a scale from 0 to 1000, 200 is good, so it'll read low, but it should still read something. If it reads close to 0, then it is most likely weak. Also check any resistors in the rectifier socket. There is often a 1 megohm or similar resistance. If it drifts, you get a dim picture. If your set uses a voltage regulator (I forgot the common number, but if someone names it, I'm sure it'll ring a bell), it could be faulty.

Does your set use a series string or a parallel 6.3 volt circuit? If it is of the parallel type, you can build a voltage doubler, and then put a resistor in series with it to boost the voltage a little (7 or 8 volts...you don't want 12.6 volts). You can also use a center tapped secondary of the medium size 12.6 volt transformer that Radio Shack sells (if you have a parallel filament circuit). Wire one half of the secondary to the filament circuit. Wire the entire secondary to the picture tube filament through an appropriate resistor. Most 6.3 volt picture tubes draw 600 mA, so it should be fairly easy to do the math for dropping 12.6 volts to 7 or 8 volts.

I have a parallel type brightner, but I really don't want to part with it.

Thomas

1/7/2008 6:54:43 PMchip
:Be sure that it is the picture tube. Have you tested the high voltage rectifier? It can be weak. On my emissions tester, with a scale from 0 to 1000, 200 is good, so it'll read low, but it should still read something. If it reads close to 0, then it is most likely weak. Also check any resistors in the rectifier socket. There is often a 1 megohm or similar resistance. If it drifts, you get a dim picture. If your set uses a voltage regulator (I forgot the common number, but if someone names it, I'm sure it'll ring a bell), it could be faulty.
:
:Does your set use a series string or a parallel 6.3 volt circuit? If it is of the parallel type, you can build a voltage doubler, and then put a resistor in series with it to boost the voltage a little (7 or 8 volts...you don't want 12.6 volts). You can also use a center tapped secondary of the medium size 12.6 volt transformer that Radio Shack sells (if you have a parallel filament circuit). Wire one half of the secondary to the filament circuit. Wire the entire secondary to the picture tube filament through an appropriate resistor. Most 6.3 volt picture tubes draw 600 mA, so it should be fairly easy to do the math for dropping 12.6 volts to 7 or 8 volts.
:
:I have a parallel type brightner, but I really don't want to part with it.
:
:Thomas
1/7/2008 7:10:14 PMchip
::Be sure that it is the picture tube. Have you tested the high voltage rectifier? It can be weak. On my emissions tester, with a scale from 0 to 1000, 200 is good, so it'll read low, but it should still read something. If it reads close to 0, then it is most likely weak. Also check any resistors in the rectifier socket. There is often a 1 megohm or similar resistance. If it drifts, you get a dim picture. If your set uses a voltage regulator (I forgot the common number, but if someone names it, I'm sure it'll ring a bell), it could be faulty.
::
::Does your set use a series string or a parallel 6.3 volt circuit? If it is of the parallel type, you can build a voltage doubler, and then put a resistor in series with it to boost the voltage a little (7 or 8 volts...you don't want 12.6 volts). You can also use a center tapped secondary of the medium size 12.6 volt transformer that Radio Shack sells (if you have a parallel filament circuit). Wire one half of the secondary to the filament circuit. Wire the entire secondary to the picture tube filament through an appropriate resistor. Most 6.3 volt picture tubes draw 600 mA, so it should be fairly easy to do the math for dropping 12.6 volts to 7 or 8 volts.
::
::I have a parallel type brightner, but I really don't want to part with it.
::
Long story short, the chassis has been rebuilt by Predicta Bill and I have gotten a prema power color brite C-501 from moyers. The picture seems better now and I can't expect a perfect picture from a 49 year old set. The focus is what I am concerned about now, figures up close look ok but foreground objects are fuzzy. I am getting a Rca wr-64b color/dor /crosshatch generator to check color and convergence. I still have to set the brightness more than 2/3 to get a brite picture,some movies are dim but cartoons look fantastic.


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