ctc12 clone beam current

[DaveWM]

I assume you mean pin 1 and 5 the cathode and the grid?

you can run pin 1 up and down with the hv adj pot. this sets up the overall bias and determines the current shunted by the tube. bigger the difference the (cathode pin higher that Grid pin) the less current flows thru the tube (to a point until its cut off completely and no current will flow). Less current thru tube, the higher the unloaded HV will be (assumes CRT is blank and not drawing any). the voltages ref in sams are "prob" just a reading with the a blank raster as most of the time there is a statement about "no signal" and using a VTVM, setup for normal viewing etc...

things to consider, the type of test equipment used (in this case its prob supposed to be a VTVM)
line voltage
no signal (unless specified like in some of the chroma test points, which is typically color bars)
+/- tolerances ofter 10-20%
resistance and voltage readings are just the starting point and not the only thing to look at if something is not working right.

[timmy]

Originally Posted by DaveWM

I assume you mean pin 1 and 5 the cathode and the grid?

yes , im sorry this test was with the tube in pin 1 and 5 to ground

[timmy]

i tried that hv pot up and down it dont swing much at all only a few volts on the grid. your opinion, about putting the 2 1.5 m resistors back in which are now 1.6 m would this just lower the hv overall or leave the 2- 1 megs in if it benefits the hv circuit.

[DaveWM]

I don't like to re engineer tv's so I would put the correct resistors in there.

That being said other that I think it will work the same, just with the HV pot in a different position to get 25kv. You will just be moving the math around a bit on the voltage divider requiring resetting the HV pot.

[timmy]

i have a bit of a problem the 6gm6 has c25 and c26 off pins 3&4 these caps go to ground the sams shows nothing else but 3-4 to ground but i am getting k readings on both pins to ground, this is not right as a .001 should not show anything to ground. this tube is ccw as the rest ? im seeing 81 k on both pins to ground..

[DaveWM]

Originally Posted by timmy

i have a bit of a problem the 6gm6 has c25 and c26 off pins 3&4 these caps go to ground the sams shows nothing else but 3-4 to ground but i am getting k readings on both pins to ground, this is not right as a .001 should not show anything to ground. this tube is ccw as the rest ? im seeing 81 k on both pins to ground..

if the filament wires are attached to the board then you are seeing the resistance of the B+ voltage divider to ground that is used to float the filaments.

[timmy]

ok that makes sence but in your video the voltage you had at pin 1-2 showed 211volts mine shows 220 volts closer to the 225 v limit 211 v would be better i would think.

[timmy]

maybe i should have changed them both c25 and 26 to be safe. if the other cap was leaking just a little bit , would this affect the heater voltage or the voltage at the shunt, like the other.this other cap is on the side of the resistor divider.

[DaveWM]

lift the all the leads off the junction of the 150k/180k resistors and read the voltage, should be around 180-190v

reattach the leads, it should not change. if it does then there is leakage, somewhere. could be those caps to ground (.001/.001/.1) or a KH short in a tube (the IF tube/shunt tube/CRT).

if it does not change you are good to go.

if it makes you feel more comfortable to change by all means have at it, just make sure the cap is rated at least 400v to be safe (double what it is likely to see)

[timmy]

i just want to cover all i can and not overlook anything. i took the 3 tubes out that use the z y connection but i would still have to remove the connection from the diode and the gound via the resistors then check those z y heater leads to ground there should not be anything readable, i hope. i will change the other cap .001 i will use a 102k 1 kv its supposed to be a .001

[DaveWM]

TAB BOOKS NO 496
RCA COLOR TV SERVICE MANUAL
BY CARL BABCOKE.

Timmy you MUST buy this book, often on ebay for $5-10$

it explains CRT bias and HV regulation the best I have ever read.

[DaveWM]

I was reading that book, the low side of the brightness pot should be -14 the high side +12. Check the peaking coils right by the 12BY7, the -14 is pretty close to what you have the high side seems too high (+20v not +12).

this could be an open peaking coil or a weak 2nd video amp.

check L12 and R61. What value do you have for R64?

[timmy]

ok ill check those resistors. and the 2nd video tube would be the 6gm6 at that cap that burned but i put another one in there. then there is the 1st & 2nd videotube which i also changed so i would think that rules the tubes out at least for now until i check the other components. ill check again but i have checked r64 several times in the past to find it was good. ill get back to you on the others.

[timmy]

ok this is what got here, L12 tests at 6.8 ohms compared to 6 ohms, c39 reads infinity, other .001 at the 6gm6 tube tests good so i left it in there, L13 however didnt test so good , 6.5 ohms down from 2200 ohms, ( 2.2k ) so i know now i need this coil 2200 ohms 120 uh . r 61 1185k ohms sams shows 2200 ohms , r 64 .732 meg looks good sams shows 680k

[DaveWM]

the L13 is fine they are giving you the value of the resistor not the coil another of sams errors of omission. I was taking a long shot trying to see if there is any reason the hot side of the briteness control was so high. I dont think there is a problem. More likely just some tube issue (weak) in the 2nd video amp.

that book I mentioned goes over much of this in great detail. I did not see one listed on ebay currently but if you check back I am sure there will be one, they come up all the time, remember it has to be the 1st volume by carl babcoke on rca color tv's.