help me ID this mystery GE roundy plz!

[Yamamaya42]

could not resist
https://www.youtube.com/watch?v=-E_g_GIEHAo
had to show some video
the bars on the sides was made by the dvd creation process, it also borked the sound.

[Yamamaya42]

damn, it seems the shadow mask is flawed on this tube
https://i.imgur.com/95YrwNE.jpg

can only be seen when there is an image on the screen.
What does RCA do? give their failed stuff to others to sell?

[SwizzyMan]

Phosphor defect. Theyre pretty common on color tubes atleast the ones I have.

[Electronic M]

Originally Posted by Yamamaya42

could not resist
https://www.youtube.com/watch?v=-E_g_GIEHAo
had to show some video
the bars on the sides was made by the dvd creation process, it also borked the sound.

It's too bad Eddie VanHalen passed.

Phosphor/shadow mask defects are not uncommon especially in early color sets. By the mid 60s things were better but lower tier brands still would have grade B CRTs into the early 70s. I've got a late 60s Airline rectangular with similar defects on its original CRT.

You can sometimes find primo sets with the issue when the CRT has been swapped.... Normally customer sets would get grade A or B CRTs but repair shops that would do slap dash reconditioning on trade ins to resell them would sometimes use grade B and C CRTs since margins were tight.

[Yamamaya42]

https://i.imgur.com/ggGHBP3.jpg

cooked and leaky, just like the ones I took out of my CTC-16XL

https://i.imgur.com/0ze8p2E.jpg

and I did say the HOT looked tired :O

new one SHOULD be here sat.

[Yamamaya42]

Just how accurate are the resistance readings on the SAMs for the tube socket points?

Example, it says pin 7 of the 1st amp should be about 150 ohms, and it's about 640 ohms, and the wave there says it should be 2.5 ptp and it was 5v, and should be -..3 and it was -5v.

And the PtP input for the 2nd video amp should be 1.8 PtP and it was just under 1.

I'm still waiting for the new 6LF8...

[old_tv_nut]

Assuming the SAMS numbers are not typos, I would expect within +/-20% or maybe 25% worst case (trying to allow for parts tolerances, tube variations, tolerance of your meter, etc.). But also watch out for circuits that have variable resistance, like contrast or brightness controls. If SAMS tells you how they are to be set, do that, but if not, vary them and see if you can get the specified reading at some setting. For example, if the video detector output p-p is wrong, is it because of AGC adjustment?

[Yamamaya42]

There is definitely something wrong with the 1st video amp, be it the tube or related circuit, for the plate voltage, which SHOULD be about 150v, is right now at 260v.
Hopefully, the new tube, which was last scanned in Florida, will fix all this.

[Yamamaya42]

General observations of the GE M939ACD.
Although it's considered to be a CTC-15 clone, this one is closer to the CTC-16, using a 6LF6 for the 1st & 2nd video amp and not a 6AW8A, The IF is an odd mix of both the 15 & 16.
The video detector circuit (diode, coils, resistors, etc ) is exactly what's in the 16.
The input wave on pin 7 of the 1st video amp was 5v PtP, and the volts was -5 Sams says the wave should be 2.5v ( this is most likely irreverent) .
The cathode resistor on pin 6 checked OK at 21 ohms.
Plate voltage on pin 9 is way too high by over 100v, R56, 10k,10w plate resistor OK. ( suspect bad tube), C33 color link cap OK.
Cap/resistor link to 2nd amp OK, peaking coil here is good, vertical blanking injection point on grid of 2nd video amp seems OK, but have not fully checked all caps/ resistors in the line yet, signal here is 30%-40% below what it should be, grid and plate voltages are nominal.
Delay line & following coil OK, tieback/feedback point ( resistors and coil) to AGC/ SYNC SEP OK, but have not checked the 40uf cap in that circuit yet, most likely OK, but will check.
ALL resistors for brightness & contrast have been replaced, including R66, the 680k one that's tied to the strong horz pulse, never quite understood what this does, but it's on all versions, if I get no improvement in brightness after getting 1st / 2nd video amps up to par, I will start looking caps in this area,
there is an obvious error in the Sams for the GE, the pulse from the FBT at the horz blanker is shown to be 145 PtP, that clearly should be 245v, based on what it is on all other versions and what I read in this on on my scope.

[Yamamaya42]

Originally Posted by old_tv_nut

Assuming the SAMS numbers are not typos, I would expect within +/-20% or maybe 25% worst case (trying to allow for parts tolerances, tube variations, tolerance of your meter, etc.). But also watch out for circuits that have variable resistance, like contrast or brightness controls. If SAMS tells you how they are to be set, do that, but if not, vary them and see if you can get the specified reading at some setting. For example, if the video detector output p-p is wrong, is it because of AGC adjustment?

https://i.imgur.com/k1AuqAi.png
Right now, the only adjustment that I think would have any effect resistance wise of pin 7 of the 1st video amp would be the R22 pot, sound reject, but I have no reason to touch it at this point, so I guess I will ignore the high ohm reading for now.

[old_tv_nut]

If you follow all the DC paths from pin 7 (grid) to ground, you see 5600 ohms in parallel with 8200 ohms and all that in parallel with the video detector diode and a few small coils. Because of the diode, I'd bet you get a different reading if you reverse your meter leads or even if you use a different ohmmeter, depending on the voltage of the meter's internal supply and its polarity.

[Yamamaya42]

Originally Posted by old_tv_nut

If you follow all the DC paths from pin 7 (grid) to ground, you see 5600 ohms in parallel with 8200 ohms and all that in parallel with the video detector diode and a few small coils. Because of the diode, I'd bet you get a different reading if you reverse your meter leads or even if you use a different ohmmeter, depending on the voltage of the meter's internal supply and its polarity.

Yes, Sams did say it was Dependent on polarity and with positive to gnd, it's much higher, I guess they took that with a VTVM, who knows, I only have digital ones, the new tube should be he Sat, if USPS does not screw that up too, we will see what happens.

[Yamamaya42]

What I don't get is that 10k 10w resistor on the plate power line to the first video amp, what is it doing with that much power?

[old_tv_nut]

What does the following circuit look like and what is the p-p voltage supposed to be?

Anyway, the DC voltage across the 10k ohm is 400-250 = 250.
250 squared divided by 10k is 6.25 watts.

Wondering if they really needed a 400 volt supply for this stage, or if it was the only thing they had, so a high-wattage resistor was cheaper than supplying a special lower voltage.

[Yamamaya42]

Originally Posted by old_tv_nut

What does the following circuit look like and what is the p-p voltage supposed to be?

Anyway, the DC voltage across the 10k ohm is 400-250 = 250.
250 squared divided by 10k is 6.25 watts.

Wondering if they really needed a 400 volt supply for this stage, or if it was the only thing they had, so a high-wattage resistor was cheaper than supplying a special lower voltage.

they basically carbon copied everything from the CTC-16
https://i.imgur.com/hzAFBB0.png
as seen here
it was easier to grab that
another thing noticed, voltage on pin 8 is also way too high, as is the source (110 in the GE 100 in the RCA) it is WAY over, 260v and shoots higher when tube is removed. Again pointing to faulty tube I think, in this GE, the 110 is sourced from the 380v source through a 47k 1 w resistor and tied to a 2uf filter, and goes to only 2 points, that grid of the 1st amp, and here, https://i.imgur.com/yKyOtr1.png
there is nothing else to pull that voltage down to 110v