Can't see it too clearly, but that's what I'm talking about.
I had a Philco split chassis set (51T-1634) with full 4Mhz luma channel that had horrible dot crawl, it was produced around 1951 or so before the advent of color transmissions. I used it to watch the nightly news for a couple months before I sold it, but the dot crawl was to me objectionable. Too bad, as that set had the most razor sharp picture I've ever seen in a monochrome set. I suppose I could have fed it with the Y line from a DVR which would have been free of any chroma mess, but it's in the past now. Oh well, I'm a color guy now!
Which brings me to color traps:
The filtering of any residual 3.58Mhz chroma signal in the luminance line, which further serves to reduce dot crawl in color sets.
All color chassis I've come into contact with have a trap tuned to 3.58Mhz in the luminance line after the first video amplifier tube, whose purpose is to remove any residual chroma stuff left over after the first stage (the purpose of A31/L30 in the CTC-2 schematic).
If this trap is tuned incorrectly, it's possible to have a mess of a picture on screen in your vintage color TV. The solution of course is to sweep the offending trap and tune it to the correct frequency, thus eliminating any residual 3.58Mhz noise present in the Y line. Most technicians these days have no idea what I'm talking about, so I will elaborate.
A sweep alignment setup is used in TV servicing to pinpoint circuits in the receiver which have a defined frequency setpoint, and ensure that they are tuned correctly. This usually takes the form of a dedicated sweep rig, with sweep generator, marker, and o-scope/detector to see what you're dealing with. This sounds complicated (and it is), but thankfully the good folks at B&K were kind enough to create a rig which does all of the above in one neat little box: the 415!
http://www.radiomuseum.org/r/dynasca...rator_415.html
This ingenious little device incorporates 3 distinct pieces of test equipment into one box, thus greatly simplifying the testing of most receivers. It has a sweep generator, marker, and also has inbuilt chroma detection circuits for use with the probe that's supposed to come with it. The only other thing you need is a scope (and possibly a auxiliary bias box, though the 415 has 3 bias supplies in it).
Basically everything is outlined in the instructions. You connect the device to your antenna terminals, and the necessary signals are passed to the chassis for use with the various probes. In this way you can set up the 415 to align a tuner, IF strip, chroma demodulators, traps, and just about any other thing you may come into contact with in your servicing endeavors. It's been an indispensable tool for me, I highly recommend it to anyone servicing sets color or not. It took me roughly 2 weeks to understand how to align the CTC-2 tuner and IF strip with it, if that means anything. I've had requests in the past to explain tuner/IF alignment, so perhaps I'll do a how-to video in the future. For now, I'm focused on color circuits.