Happy Halloween! NTSC "Pumpkins" slide on CTC-5

[Penthode]

Originally Posted by old_tv_nut

Note that there was a service bulletin from RCA suggesting rewiring the CTC-5 contrast control ala the CT7 also. I rewired mine and unfortunately got it backwards, so max contrast is CCW, but it's too much hassle to fix unless there's some other reason to pull the chassis.

Sorry. But I found that funny considering the difficulty I had making extension cables and propping up the chassis so I could test it. I made a high voltage extension with a length of high voltage wire and connectors made from strips of metal from an orange juice can shaped to make a receptacle for the wire to the CRT and a plug to fit the socket at the HV rectifier. The receptacle is covered with multiple layers of heat shrink tubing. It works well with no corona discharge and allows me the flexibility to prop the chassis vertically to the rear.

Perhaps if there is sufficient improvement with the DC coupling it may justify your pulling the chassis again?

[old_tv_nut]

No need to be sorry, I laughed at myself when I did it.
Will be following your results closely.

[Electronic M]

I may try this on my CTC5 specials. I've already adopted the CTC7 adjustible HV reg circuit.

[Penthode]

I spent the last few days working on the CTC5. The CRT is the original 21AXP22A with a date code of 56-30 ( 30th week of 1956). The emission on the three guns is good but the red gunntakes about a minute longer than the blue-greento come up.

The change made to the video amplifier to improve black DC level maintenance appears worthwhile. I ended up removing the 4700 ohm load and the ceramic 0.01uF capacitors as they appeared to do nothing.

I followed the RCA supplement procedure for greyscale. The CTC5 does not have The convenient setup switch. But the process from the manual works well. I will summarize it below.

For the Super chassis (without background control). This assumes the recommended contrast control modification has been done.
1. Set the three screen controls fully counter clockwise and the green and blue background controls backed off about 30% from full clockwise.
2. Unplug the tuner IF connector to provide a no video raster.
3. Set the brightness control so the the red gun grid bias is -70v.
4. Advance first the red screen control until a red raster becomes just barely visable.
5. Advance the green and blue screen controls so that the raster is dark grey/ black.
6. Advance the brightness control until the raster is bright without blooming. The touch up the blue and green background controls until the raster is white.
7. Reduce the brightness to the point the raster is about to disappear and touch up the blue green screen controls only for dark grey/ black.
8. Advance the brightness and touch up the blue green screen controls for white.
9. Re insert the IF link connector and reduce the color control to check the black and white video. You may wish to lightly adjust the green blue background controls for white highlights.

The deluxe chassis has a red background control. It's initial set up is as follows:
1. Set the brightness control to minimum.
2. Set the red background control for red gun grid bias of -90v.
3. Continue with the Super chassis instructions Step 1 above.

After some effort, the CTC5 is looking pretty good. The HV is 21.5kV and holding steady. (I earlier inserted a solid state HV rectifier which suffers less voltage drop and eliminates the filament load on the high voltage transformer.

Here are,a couple of snapshots tonight.