A question for you long time experts

[DaveWM]

can you expand on that circuit Andy?

[NewVista]

Some vid amps have Hi res across coupler, is this for partial DC Rest ?

For example, CTC 5 has ~1 meg across Y coupling cap & 390k across chroma drive caps.

Does CTC 16 have full DC Rest ?

[old_tv_nut]

Originally Posted by Zenith26kc20

Does the RCA TM21 monitor use the same video output setup like the CT-100?
The CT-100 appears to be akin to modern solid state drive to the CRT with "Y" and color on the cathodes (hope I'm right but I'm at work away from my CT-100 schematic) (I know, blasphemy) from what I remember. The later color sets had "Y" on the cathodes and color on the control grids.
Both color and "Y" appear to be capacitor/resistor coupled (at least on my Magnavox T933 and Zenith N chassis.

I'm away from my schematic too, but I think the CT-100 had R,G,B drive to the grids, and the cathodes were just DC (?)

[Zenith26kc20]

It's always fun to dig around the archives! Found the 1954 RCA Practical Color book. The CTC 100 cathodes are DC to ground. They are decoupled by a 20 mfd cap with a 8200 ohm parallel resistor. The grids have around 75 volts on them. Very different than later sets!

[andy]

---

[jeyurkon]

Thanks for the diagram. This thread prompted me to look this subject up and your simple suggestion makes a lot of sense. Given the low cost, I wonder why it wasn't implemented originally?

John

[Zenith26kc20]

Going to try it on my Motorola TS-4 and will see what happens!

[Zenith26kc20]

The mod is in and seems to work. There is more picture information. My 7 inch tube is dated 1943 so it takes a bit to wake up (it's older than me, but not by much
Now I'm looking to try it on my Zenith Square tube. It looks like it's going to fun.
By the way, I looked at the TM21 (hope those #'s are right) monitor.
Now that's a bunch o goodies in a cabinet!

[old_tv_nut]

can you post som pics?

[Zenith26kc20]

I'll bring the camera tomorrow and try to get some postings.
Strange thing, maybe coincidence, but vertical and horizontal sync seem more stable. Can't see how that would be but....

[cbenham]

Originally Posted by Zenith26kc20

Does the RCA TM21 monitor use the same video output setup like the CT-100?

Actually better than the CT-100. There is a full I-Q decoder with matrix amps that recombine the color signals with the luminance to feed real R-G-B signals to the CRT, not combined inside it.

The DC restorers for each signal are full wave back porch clamps that provide 100% DC restoration. When the image goes to black on this monitor IT GOES TO BLACK!

It will also warm your livingroom nicely on those cold winter nights, especially if you live in Wisconsin, Minnesota or Michigan!

[Zenith26kc20]

Here is the picture of what people here call "the eyeball"!
One day this set will go back in it's cabinet but customers love the looks and are still amazed that it plays!!!
I tried to post an before picture but the upload kept failing. I have to find out what is wrong and will post the non dc next. There is a picture of the set without dc restoration but it's under VT71m-a