My CTC-16XL Project.

[old_tv_nut]

Did you mean you read 147 v DC?

[Yamamaya42]

Originally Posted by old_tv_nut

Did you mean you read 147 v DC?

yes, its at 147 v DC still and when i hooked a o-scope i saw a 13 volt wave there left side of c135
Cathode @ 6v , grid @ -86v with 240v waveform


edit
r203/204 new and V21 new.

[old_tv_nut]

Originally Posted by Yamamaya42

yes, its at 147 v DC still and when i hooked a o-scope i saw a 13 volt wave there left side of c135
Cathode @ 6v , grid @ -86v with 240v waveform


edit
r203/204 new and V21 new.

As you are getting a good blanking pulse, my bet is that the designers expected the variation in the range you are seeing and determined that the circuit would still work properly with this variation.

Edit: if you have extra tubes, it might be educational to plug a few in and see if the DC changes but the pulse is still OK. If you don't have extras, you could still experiment by exchanging V21 and V20.

[Yamamaya42]

Originally Posted by old_tv_nut

As you are getting a good blanking pulse, my bet is that the designers expected the variation in the range you are seeing and determined that the circuit would still work properly with this variation.

Edit: if you have extra tubes, it might be educational to plug a few in and see if the DC changes but the pulse is still OK. If you don't have extras, you could still experiment by exchanging V21 and V20.

Tried that, did not hep much, I do have another one ordered.

Also, it does not help much that I have things bypassed and have video fed in, so that MAY be part of it, it is weird, some times the retrace lines are seen, other times they are not, not sure why it is doing this.

[old_tv_nut]

Originally Posted by Yamamaya42

Tried that, did not hep much, I do have another one ordered.

Also, it does not help much that I have things bypassed and have video fed in, so that MAY be part of it, it is weird, some times the retrace lines are seen, other times they are not, not sure why it is doing this.

Well, I guess you will need to continue poking around to see what is changing between when retrace is visible and when it is not.

Is it dependent on picture content (only shows up on dark scenes or light scenes)?

Is your video input at the first video amp grid (pin 7) the same DC and peak to peak as shown in the schematic? (0v dc and 3.5 vp-p)?

Is your video input signal DC coupled or AC coupled? The video DC coupling in these old sets is usually about 85%, which means the brightness (black level) drifts up a bit on dark scenes and down a bit on bright scenes. Two things could affect this with your external video input and make it worse:

1) If the DC level at the first video is wrong, you will get the wrong DC level at the cathodes and have to compensate it with tracking adjustments, which may make you run out of blanking headroom in certain scenes.
2) If your video input is AC coupled, the black level will drift up and down strongly depending on overall scene brightness, and in dark scenes may drift so high that you run out of blanking headroom.