My CTC-16XL Project.

[Yamamaya42]

still not sure what i should see on pin one of V21, voltage is still high, in ref to SAMS 147v
waveform there is about 12v ptp, not sure if this is normal.

[old_tv_nut]

Not following what 147 v waveform you are referring to. According to the schematic, pin 1 of V21 (V21a plate) should be at 115 v dc. Since it is coupled to the color difference amplifier cathodes by C 135, it should have the same peak to peak ac waveform as those cathodes, which the schematic shows as 15 volts peak to peak. The 12 v p-p you measure is very reasonable and the total p-p will depend also on the amount of color in the image as well as the setting of the color level control. With the color turned all the way down, you should see just the blanking pulse, which by itself appears to be 10 or 12 v p-p.

[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.

[old_tv_nut]

By the way, a difference of 147 vs. 115 volts could result from a 13% variation of triode characteristics, which is probably not a totally unreasonable variation from the tube in the set SAMS measured to one you might have.

[When I was in school, I pissed off the lab instructor by asking how big the variations bewteen tubes of the same type were. He apparently didn't want to admit that he didn't know either.]

[old_tv_nut]

I looked up the 6GU7 data sheet and it says the plate resistance is "5500 ohms (approx)" but they don't say how approximate. Isn't that cute!

[Electronic M]

Are you aware of the effects of macrovision copy protection on tube sets? That will cause retrace lines that come and go despite a set working properly.

[Yamamaya42]

Originally Posted by Electronic M

Are you aware of the effects of macrovision copy protection on tube sets? That will cause retrace lines that come and go despite a set working properly.

i'm using a dvd that i created myself, so i know that is not an issue .

[Electronic M]

Originally Posted by Yamamaya42

i'm using a dvd that i created myself, so i know that is not an issue .

The video injection schematic looks good.

If you have a DTV box I'd try that to confirm. The DVD recorder/VCR and computer methods I have to create DVDs give the option to make a disc with the macrovision flag set (though they just call it copy protection or something like that). That could be set default to on in your system or you could have a DVD player that constantly outputs it. DVDs don't come encoded with macrovision and only have a flag bit that tells the DVD player to create and mix in the macrovision signal. There are some DVD players where one can easily set the machine to always neglect adding macrovision and the other way around is not impossible either.

[Yamamaya42]

=====
Electronic M
Why not just use a .1uF cap to couple the transistor amp output to the grid?..It will block DC from changing grid bias, should couple the video just fine and RCA colors all had some form of DC restoration that negates and need for DC video coupling in the early stages of the video chain.
=======
old_tv_nut
If you use a coupling cap and remove L9, you will need to add a grid bias resistor (say, 100k) from G1 to ground.
=======

here is how it is right now,
https://imgur.com/NosUKXZ
https://imgur.com/wQj8vGR

the .1uF cap is on the amp pcb i made, the 100k resistor on the set, on the bottom of the tube.

the .1uF cap is cheap low quality, i did not think it mattered that much,
also , since it is a temp setup right now, i am using a low quality cable to to patch it over.

Would the cap be better suited on the bottom of the tube near the 100k res?
or leave it on the amp PCB and just try a better quality cap and cord?

[Yamamaya42]

I'm not entirely sure that is a macrovision issue or not, but it can be tested.
The videos on the test DVD were originally MKV format, and converted to DVD using Freemake Video Converter, there is no option for copy protection in the burn setting, nor region code. So it is most likely off, but can't be sure.

I do have to option of trying my Pioneer LD-V8000, this outputs pure analog video with no copy protection, and can go with helping with what I'm suspecting that this is a symptom of something else I have not found yet.

I think just to err on the side of caution, I'll replace that cheap ass .1uF cap ceramic cap of unkmown tol on the amp, with one of the better film ones I have 10%, and wire in the video cable I intended to use for the final setup and see what happens.

[Yamamaya42]

no change using the LD input retrace lines are still there
https://imgur.com/LCoR4sm
changing the cap and cable on my video amp did not help much.

I DID nitice something however, moving the wires to the CRT socket drastically made an effect in the screen color level.

now IDK if this means there are bad connections in the socket on the CRT, or if there is a problem with the socket itself, I DO have a brand new CRT socket, and it wont be too much effort to splice it on, but i have also read of there being problems with fractured solder on CRT pins, could it be both?

I'm not sure, but i'm willing to bet this is the cause of the retrace line problem.