Rca ctc-5

[DaveWM]

color looks great, but it was a bit weaker than before (which makes sense as the elipse was larger than the circle) a tweek of the ACC (which controls the chroma band pass amp gain based on burst amplitude) fixed that.

I still plan to make a custom top for the fly cage, it will have a plenum with a built in filter to help keep the fly temps low. Even with the low current thru the fly (about 175ma) it gets hotter than I like after extended viewing (hit about 165f after about 1 hr).

[old_tv_nut]

Originally Posted by Penthode

... Also to regulate, the 6BK4 does not sense current, it senses voltage. The boost B+ voltage is sensed which should be directly proportional to the HV.

You are correct - don't know what I was looking at before.

[DaveWM]

I also found the vectorscope useful for touching up the matrix balance pot on the back of the chassis as well. this pot varies the cathode bias resistance of demodulator tubes. the effect on the vector scope is to squash down the circle pattern to get it as round as possible. I found that by adjusting the top core of the CW driver trans and the matix pot at the same time was the best way to setup the matrix.

[old_tv_nut]

I assume with the vectorscope you are using a gated rainbow pattern producing a "flower petal" vector display.

If the drives required for the red and blue guns were equal to make white, then the pattern would need to be elliptical, with the B-Y gain = 2.03/1.14 = 1.78 times the R-Y gain. (These are the ratios dividing the B-Y and R-Y axes before the chroma is modulated.) However, the red phosphor in the early tubes is weaker by about the same ratio, so equal (approximately) is correct (that is, the pattern is circular).

By a fluke of changing both the green and red phosphors in later tubes, the red gun requires less drive to make white; so there was a fix to reduce the red luminance drive; and at the same time, the yellower green sulfide phosphor means that the extra R-Y drive is still needed, to approximately compensate by making the difference between reddish and greenish colors greater. So, the matrix adjustment does not have to change, and can stay with a circular pattern when a new CRT (e.g., 21FBP22) is substituted.

[DaveWM]

Yes I am using the gated rainbow pattern. The petals are roughly circular now, but not very pretty (somewhat misshapen pointy, sickle shaped), so I am sure more work could be done, but I am not sure if its a fault of the demodultor or the chroma signal coming from the video detector or maybe just the design. I plan do do an IF and Chroma sweep alingment later with a BK 415.

It may be fun to play with some of the chroma tubes just to see the effect.

[DaveWM]

I was a little bit surprised at how small an adjustment was required to from practically no green (green would look either blue or brown depending on tint setting) to perfect green, the adjustment was about a 1/4 turn and it is very narrow. I have had quite a few sets that had brownish greens, so next time before I touch anything I am just going right to the vectorscope and the gated rainbow to see whats happening. But you mention that in some cases a round petal design is not optimum. Most of the CRTs I work on are the 21fjp22 or 23vadp22 types. I have a both grey face and green face types of the roundies.

[old_tv_nut]

Originally Posted by DaveWM

Yes I am using the gated rainbow pattern. The petals are roughly circular now, but not very pretty (somewhat misshapen pointy, sickle shaped), so I am sure more work could be done, but I am not sure if its a fault of the demodultor or the chroma signal coming from the video detector or maybe just the design. I plan do do an IF and Chroma sweep alingment later with a BK 415.

It may be fun to play with some of the chroma tubes just to see the effect.

it's hard to say exactly what shape the petals should have. Remember that the signal that's being gated is changing phase across the width of each bar, so even if phase response of the chroma is perfect, the trace will go outward from the center and back to the center while changing phase at a rate determined by both the varying phase and the final demodulated chroma bandwidth. Sickle shape is an indication of some phase distortion (rising waveform is different from falling), but this can be affected by fine tuning, adjustment of the sound trap(s), etc. and can be very hard to get perfect. On the other hand, if it's very bad, it will show up as edge discoloration on strongly colored objects.

If you really want to look for distortions, you need regular color bars, which have the same phase across the whole bar. Then you can make out things like the green-magenta transition not going directly across the gray center point, or other transitions not going straight between bars.

[old_tv_nut]

Originally Posted by DaveWM

I was a little bit surprised at how small an adjustment was required to from practically no green (green would look either blue or brown depending on tint setting) to perfect green, the adjustment was about a 1/4 turn and it is very narrow. I have had quite a few sets that had brownish greens, so next time before I touch anything I am just going right to the vectorscope and the gated rainbow to see whats happening. But you mention that in some cases a round petal design is not optimum. Most of the CRTs I work on are the 21fjp22 or 23vadp22 types. I have a both grey face and green face types of the roundies.

The circular case has been closer to correct than the case of greater B-Y for all tubes, since there never was a tube combining rare-earth red and NTSC green. The early tubes (weak red with NTSC green), and the later tubes (sulfide red or rare earth red with sulfide green), both require something closer to a circular petal pattern.

You are lucky you aren't looking at a Motorola with the single tube chroma section - that got G-Y off the cathode, where it was weaker than nominal and matrixed from the wrong proportions of R-Y and B-Y, resulting in that "brown or blue" syndrome you observed.

[DaveWM]

I next tried a reg NTSC color bar pattern, pretty good, but very noticeable ringing was observed, it was tunable but as crystalization was approached it got pretty bad. Turned out to be the 1st IF (stared with the 3rd and worked back subbing as I went). I am glad I have a good supply of tubes to sub.

It just keeps getting better in small increments.

I do get a little bit of color bleed that shows up more on the NTSC as there is no gating but most of my old color tube sets do this to some degree.

There are quite a few check points for setting up the chroma, but I am running out of gas and don't feel too inclined to mess with it much more.

[DaveWM]

the ring is still there, slight but still there (its a ring not a ghost as you can see multiple diminishing rings. Its tunable so I am pretty sure its in the IF. It looks like this set relies on pressure grounding of the pcb's (not the solder stakes like later RCA color chassis). Any one with some tips on what I may look for as far as IF ringing (of if there is another area that could cause ringing? its in both the luma and chroma. I don't think it would be delay line issue since it is tunable.

[old_coot88]

Originally Posted by DaveWM

the ring is still there, slight but still there (its a ring not a ghost as you can see multiple diminishing rings. Its tunable so I am pretty sure its in the IF.

For the heck of it, try subbing the 3rd IF again (i know you subbed it before and the main culprit was the 1st IF). I've had a number of cases of ringing being caused by the 3rd IF tube.

[DaveWM]

I will try a few more OC and report back later.

[DaveWM]

did not get to more tube swapping but did notice some odd voltage on the video amp (6aw8). the screen was way high, like 210 vs 180 and the plate was low 110 vs 150. I checked the voltage divider on that tube and found the 15k was 11k and the 56k to ground was 65k. Not a lot but in those direction it would add up to too much screen voltage. I went ahead and replace those two ( had some old school 2watt carbon comps on hand) and check it again, much better screen at 178 and plate at 138. Seemed to help the video out, brighter and the contrast control is not as sensitive anymore, but still has a good range.

this all stemmed from what I thought was a bit dim of a pic, I started with checking out the video out, then moved to the video amp. Interesting effect of the change was before the fix I thought I had a slight tracking issue, as increased the contrast, the green highlights seemed to worsen (was checking by watching a B&W program. I just assumed it was a CRT issue. After correcting the video amp tube (and the contrast seems to work "better") I don't notice the green highlights happening. I spent a LOT of time trying to setup the the CRT drive pots to get rid of problem before. Perhaps it just not as much drive at the CRT cathodes, but it def is better.



Its fun to check things out, make a few changes check again, to slowly see improvements. I think it may add to overall trouble shooting, by being able to see direct cause effect. Not perfect, and certainly no substitute for good trouble shooting technique, but fun non the less.

[DaveWM]

more intresting tidbits, looking over the schematic, I can see the brightness control gets it neg voltage for low brightness from the horz out grid (filtered thru a .22 cap and 470j resistor. I am pretty sure I increased this neg voltage from the -40 to something less (more neg) when I was changing the plate load resistor in the horz osc in a attempt to increase drive to the horz out. Later CTC get this neg voltage from the grid of the blanker tube. I think I will check the later CTC-7 and see if it makes any changes for the great neg voltage at the horz out tube shown on that schematic (and if there is any changes in the circuit that taps this to supply the brightness control with its neg voltage).

[DaveWM]

tried a few more 3rd if tubes, found one that got rid of the rings. I think any more improvement will have to come from a full alignment.