Timmy,
Check your email at 1:20 pm. I scanned a Magnavox "series 45" schematic (CTC16 variant) which you have. The only thing is, there are no voltages on the tubes, only sources like 405 volt supply, etc.
I am ALSO sending a series 41 (similar to CTC12) schematic which HAS VOLTAGES on all the tubes.
On a 41, the blanker feeds into demod tubes' cathodes and the CRT bias sets the bias on the CRT via the B&G drive controls.
Also the 41 schematic shows you CRT voltages:
cathodes =322 volts
G1s = 195 volts
G2s = 700-735 volts

The 12GN7 should measure about 250+ volts on plate pin 7 if too low, pix is bright, too high and pix is dark.
Dont forget that 100 mf @ 25 v cap across the contrast control, jump in a new one

Whatcha got for volts on CRT pins?

ok well 100v on the G1 is clearly the problem, so now you need to check all the pin voltages on the 6GU7's these are the difference amps. I am still a bit lost since I thought you said you had over 200v on one side of the 27K power resistors. If that is the case you should have the same voltage (200v) on the G1's.

the g1 166v-171 cathodes 305v -310v all plugged in . the contrast i touch a cap at the contrast pot and gets nice bright only for a second. g2 anywhere between 546v and 1046v depending where the drives are. the 27k resistor i was talking about was the gig single 27k high wattage resistor , had 405 on one side and i think it was 244 on the other.

the brightness increase is due to the momentary short of the cap on the cathode of the video out. changes the bias of the tube, causes it to conduct hard, drops the plate voltage thru the load resistor, direct coupling to cathodes result in lower cathode (momentary) at the CRT, changes the bias to more conduction (less difference in G1 to K) so more eletron flow in the CRT.

I would start with the assumption that the problem is in the video out, so try a new video out tube. check voltages of that tube as well.

You should also try a new blanker tube since it is part of the crt bias circuit (unlike the CTC-12 this set uses G1 voltage adjustment to set CRT bias not the K's).

if the capacitor i use to jump in on the contrast control has a charge in it the screen gets really nice and bright but for a second. it almost seems as if there is a source to the contrast thats missing.

12gn7 pins- 1 6.15 v 2 4.30 v 7 255 v 8 122 v 9 0 v

Does the contrast control work?

deleted I was wrong about a pin

those all look pretty good, if anything its driving too hard.

the contrast one way with the dark pic is one thing but the other way its so dark not worth trying to see.

power off, pin 1 to ground video out resistance reading? leave it connected for a min to stablize.

196.1 ohms pin 1 to ground after a moment connected.

zero ohms with tube out.

try a new blanker, and check the pin 7 (grid) of one of the diff amps (6Gu7) voltage. blank raster. check voltage with max and min CRT bias

dont know if this is of any help but when this set was always first turned on it was missing a color until about 30 seconds of being on so i thought it may have been one of the diff tubes taking longer to heat or conduct.

should have no effect.

6gu7 pin 7 bias down 1.325v bias up -3.53v no diff bright up or down.

if new video out and blanker tubes do not help. I would focus on the crt bias circuit.

the only thing I can see in there is a pot that goes to a .22 uf cap (chroma board up front on right viewed from back) and a 220ohm resistor.

outside of that I am stumped.

ok the 220ohm checks 194ohms so thats good and the .22 i checked with my mfd dvom checker and it came in lower then the cap i have that is good. i dont know if the little difference in capacitance will make a difference but i can change it.

i thought if you pull the blanker tube out the screen is supposed to black out. well it dont its all green and bright

that tube is also one of the difference amps.

The blanker 6GU7 is also the G-Y demod amp, so that makes sense. what happens when you pull the other 6GU7? Bright magenta, right?

pin 8 voltage? crt bias up crt bias down?

pin 8 bias down 6gu7 7.35v bias up 5.95v

what if i was able to get pin 7 voltage of the 12gn7 down to maybe 185v instead of 255v. the lower this voltage the brighter it should be, maybe. but then again how would i do this anyhow.

the silvertone at full brightness is around 145v at pin 7 of the 12by7 if this is where the problem is in this maggie, video output, then maybe it would work ? i checked all the resistors around the 12gn7 tube and found not a thing.

again, you need to try a different tube. a weak video out tube will allow the plate voltage to be excessive

i did

Try a new audio output tube.

audio output , lol,???????

:scratch2:i thought about adding more big vintage speakers too but realized that wouldnt work...

a 1 meg ohm 1 watt resistor from pin 7 to ground should drop it some......... :smoke:

this set uses a stacked B+ from the audio out to supply the screen voltage of the video out (as well as other tubes). It also supplies the hot side of the brightness control. You should be able to locate that 3.3 meg now, it has the 135 (or what ever is the output from the stacked B+) on one side the other goes to the brightness control.

Sams shows pin 7 of the 12gn7 to be 300V. Pin 8 should be 135 volts, which comes also from the cathode of the audio out tube.

so if i have 122 volts at pin 8 would this suggest that the 3.3 meg resistor went up in value ? would this resistor be on the audio board or the chroma ?

the only 3.3 meg resistor i found in the chroma board near the video output tube has 124.4 volts on one side and is the same as pin 8 of the video tube. the other side of that resistor is 4.48 volts. i didnt pull it to check yet but the voltage is the same as pin 8 where its supposed to be 135 volts.

Since brightness is the issue, I would focus on the brightness circuit.

you tried a new video out tube (weak would reduce brightness)
so next look at the brightness control which sets the bias of the video out tube.
this is done via a voltage divider of 3.3meg and 330k with a source voltage of 135v

The next logical things to check would be:

135 source (stacked B+ supplied by the audio out tube acting as a voltage divider). that's a little low but prob not enough to cause a problem. A sub of the audio out tube may increase the 135v source.

The 3.3meg/330k voltage divider is where I would look. Since its unlikely the 330k has dropped (which would need to be the case for it to cause the low brightness) I would test the 3.3 meg (OUT OF CIRCUIT). If it has drifted high significantly that would reduce the voltage available to the high side of the brightness circuit.

The trouble with going strictly with the sams for voltages is there are a lot of variables so they can only be a guide. After that you need to understand how things work and use reasoning to try and narrow down the problem. Like if brightness is low look in the brightness circuit.

the 3.3meg i found in the chroma board is probably the one you are talking about so ill lift a leg and check it but this resistor is the one with 125v on one side. the audio out tube in this set is not called that its a A F output i think thats the one your refering to. the onthers are sound IF and sound demod. this resistor dont have high voltage on both so shouldnt it have 135v on one side already if that voltage was there ?

ok another audio tube did nothing so ill move to lift a leg of the 3.3 meg and check it.

6GC5 the big tube on the audio board.

The 3.3meg resistor has one side to the 135v source (provided by the 6GC5 acting as a voltage divider in a stacked B+ supply).

The other side of the 3.3 meg connects to the 330k resistor to ground.

the brightness control gets it voltage from the junction of these two resistors (a 10/1 voltage divider). If the 3.3meg drifts high the junction of the two (330k/3.3meg) will have a lower voltage for the brightness control to max out at, resulting in a dimmer pic. If the 330k drifts high the reverse is true the junction will have a higher voltage, brighter pic. if the 330k goes low, the junction voltage will be lower, if the 3.3 goes low the junction voltage goes higher. Look up voltage divider for how this works if the above is not clear.