ctc12 clone beam current

[DaveWM]

look around the junction point of the two 1.5 meg resistors, IF your set has one it will be there, but I don't think it is, if its a true clone of a CTC-12. I really doubt it could be the problem unless it has burned and gone down in value. Note it was not on earlier models.

[timmy]

i dont see it on the sams and i dont ever recall seeing anything else besides those 2 1.5 s . could the brightness pot be bad in some way, ill have to check it if it seems that this may be an issue.

[timmy]

with those voltages at the 12by7 not right im wondering even though the issue with the cap in the IF being shorted had anything at all to do with this latest problem by taking something out or a cap or resistor in some way even with the short only affecting a few filiments. and with this problem it does seem like it would affect the hv even in a small way would be a big deal by using up any surplus hv to be used when needed if the crt is being driven hard then there would be a loss of regulation, possible ?

[timmy]

c26 burned what are the odds of c25 leaking in some way or would it have an affect on these voltages?

[DaveWM]

I dont think there is anything wrong at this point with the HV, if you can get a decent looking raster and 25kv and it stays 25kv as you adjust the brightness up and down, then its working as designed.

The issue I think is a CRT bias prob, maybe a gassy CRT, something causing the problems getting the correct voltages to correctly drive the crt.

The HV holding steady from fully dark to full raster is key. The next issue is why the CRT cathodes (yellow) have to be so low to get the crt to conduct. That brightness range sure seems excessive I think you had -19 to +17 on the grid of the video out tube (based on the brightness pot). I don't recall checking that but it sure seems like a lot.

[timmy]

yes the 19 and 17 with the brightness at max and was able to bring the voltages near where they should be using the bright pot and raising the bias was ok and was also able to see the rgb lines in setup because the bias was up some and helped see those lines . but im sure the set was not designed to have the brightness halfway because if it moves then i would have to check voltages to get it back. almost as if the pot is raising to much, i dont know... as for the hv it starts out under 23kv and warming up it goes up but the key here is it dont jump like it did befor and sometimes it will go over 25kv and other times it wont so maybe there is something else going on here.

[DaveWM]

you should do some resistance checks of the 12by7 per the sams. the grid adjust the brightness pot while checking pin 2

[timmy]

ok ill do the resistance check on 12by7 per the sams, and ill run the set and monitor pin 2 voltage at the tube while lowering and raising the bright pot and note the differences. just want to make sure i got this, lol, lol.....

[DaveWM]

you could try this

brightness all the way down

service switch in service mode

advance screen drives one at a time to produce barely visable line

if any color can not produce line advance bias pot just until it does

adj all drives for barely visable line

back to normal mode

advance brightness pot just until normal viewing brightness

monititor HV and see if its holding.

if the above works then perhaps there is a problem with either:

brightness pot
grid emissions on video out.
check the plate voltage of the 6AW8 2nd video amp pin 3 per sams 30v with no signal present.

[timmy]

forget getting the lines as i raise the bias and again the blue rides in with the red the hv is up then its down bias up with the bright up hv droops as it did. i was only able to see the lines befor when the bright was adjusted to the voltages at the 12by7 that were close but its nopt working that way same as befor.12by7 pin 1-392 ohm 2-.530 meg 3 .4- fil 5 -fil 6- fil 7-6.40k 8 -3.44k 9-.4 now the 6aw8a i have a sub in there 6lf8 or i could put the right one back in, pin 3 bright low 43.7v high 38.8 v 12by7 pin 2-bright screen 20.75 v dark screen 12.5 v

[Bill R]

12BY7 pin 2 = 20volts? My 12 schematic shows -1.7 volts. Negative in relation to the cathode.

[timmy]

im sorry all you guys this set when its done will be for sure a learning experience for us all, this set i guess has been down the road a few times or someone at one time didnt know what they were doing and really messed it up and now it needs the pros, lol lol... maybe c39 slightly shorted.

[timmy]

dont know if this helps rule out a gassy crt but with the crt cap plug off the voltages at the 12by7 dont change they stay the same as i took the readings again, this time pin 1 has 0 volts pin 2 -12.5 low bright and 20.75 volts bright high pin 7 145 volts pin 8 134 volts. seems there is something else going on in this set because these voltages are certainly not right, since pin 1 looks like it should have 10 volts and #2 and #7 are the other pins with the wrong voltages.

[DaveWM]

it may take a few days, but hang in there.

I plan to make a video showing all the pin voltages on the CRT of my working well CTC-12 that will give you a good frame of reference.

Note sams voltages can be all over the place, they are way off compared to the RCA field guide as an example.

Esp CRT settings since they have to be tailored not only to the CRT performance but many other variables (not the least of which is individual taste of "correct" brightness).

[timmy]

i went back and double checked the pin 5 of the shunt voltage is 380 volts while pin 2 is 391 a difference of 11 volts compared with 370 and 385 is a 15 volt difference. just figured i would check to make sure nothing else happened there since i had some time to do so. i dont know if a few volts difference there would make much difference with the hv.