CTC-4 Director 21 - Page 6 - Videokarma.org TV - Video

miniman82 · #1 09-03-2016, 04:18 AM

If it's a B+ relay, you need to short across it to form the capacitors initially. The inrush current is what made the fuse pop, if you find it a repeated problem add an NTC to the line.

SwizzyMan · #2 09-05-2016, 10:50 AM

Or I might just delete it completely. Sure soft start is good, but it's not going to be used that much to the point when soft start may be needed.

SwizzyMan · #3 09-05-2016, 07:39 PM

so I shorted out the relay to simulate having no B+ relay at all. Also I switched the polarity of the silicon diodes to the band end facing towards positive. I powered it up and no action whatsoever. No pilot light no tube filaments. But the HOT damper and I think the shunt regulator tube filaments are glowing. I think the diode polarity is wrong, or i killed the filament winding on the power transformer.

ChrisW6ATV · #4 09-05-2016, 08:33 PM

There are two "fuses" in the filament circuits that are actually pieces of fine wire (30 gauge maybe?). Check those; one or both may have blown.

SwizzyMan · #5 09-06-2016, 04:06 PM

Y leg of the filament supply had a blown wire fuse. Temporarily twisted it together for a power up. Filaments are back and HV is back and strong. Filter cap recap finished. Might be ready to shove the chassis back in and see what the CRT has to say. Still tests wacky on 6.3 but springs to life at 7v.

Electronic M · #6 09-06-2016, 09:46 PM

Well if the tube is dim and won't focus well at 6.3V you could always try boosting to 7V later.

SwizzyMan · #7 09-10-2016, 12:19 PM

Here are some shots after the filter caps were replaced. Produces a crystal clear B&W picture, but color isnt looking good. Have to pretty much turn the color knob all the way up to get any color, but the hue is all wrong which I contribute to purity issues since the set is in a different position than the one it was in the last time it was powered up. Still have that pesky interference that comes in when the color is turned on. And it looks like the element on the electron gun is a bit discolored so that may explain why this tube is a bit weak at 6v. Everything is going well so far. Now I need to do a full recap.

SwizzyMan · #8 09-11-2016, 11:46 AM

Ive noticed that this crystal in the color circuit rattles when I tap on it. This doesnt seem right.... Might need to buy a replacement. This might contribute to the incorrect colors.

old_tv_nut · #9 09-11-2016, 12:23 PM

If the oscillator doesn't quit when you tap on the crystal, it's still OK. Just stop tapping on it in case you might break it.

SwizzyMan · #10 09-11-2016, 06:35 PM

Well Hopefully the chroma issues will clear up once I do a recap. I really hope I dont need to do an alignment. Put the chassis back on the bench and I'm going to order a full set of caps soon. Hope to get this working before the Christmas holiday season.

SwizzyMan · #11 09-18-2016, 05:15 PM

Replaced about 15 of the paper caps so far. Probably going to have to fix my filter cap arrangement, kinda sloppy. The recap of the paper caps is coming along nicely. Most of them seem to be original caps. Bet I could sell these two bumblebombs for a pretty penny to the audiofools.

More to come later.

SwizzyMan · #12 09-20-2016, 03:22 PM

I have noticed something strange. I was trying to figure out if my chassis is a early or late production chassis. Reading Bob G's article on CTC-4 chassis variants determined that my chassis was an early production chassis. One thing I have noticed is that the RCA service manuals and schematics calls for a 3.58 MC oscillator crystal, but the sams calls for a 3.579545 which is extremely close to 3.58 Mhz. This crystal seems to be a factory original part of the set, but I am confused as to why there isnt a 3.58. Maybe RCA ran out of 3.58's and used 3.579545 to substitute. I must also mention that the crystal in the set rattles when I lightly tap on it.

old_coot88 · #13 09-20-2016, 03:39 PM

3.58 is simply the rounded-off figure. "Three fifty-eight crystal" or 'color crystal' is all the same thing.

Electronic M · #14 09-20-2016, 03:36 PM

The difference is because of a mathematical practice called Rounding....In many engineering disciplines (including electrical engineering) rounding to 3 digits is common practice.

One drawing just has an unnecessary number of sig figs.

old_tv_nut · #15 09-20-2016, 05:33 PM

If the oscillator uses the crystal alone as a series resonant element, the crystal is tuned to be series resonant (a short circuit) at 3579545 Hz. However, nearly all chroma oscillators use a crystal in a "parallel resonant" mode. I put "parallel resonant" in quotes because the crystal is not tuned to be parallel resonant in itself, but to be inductive, so it can be either series resonant or parallel resonant when combined with a small amount of capacitance (consisting of both strays and discrete separate parts). In this mode, the crystal acts as a very large inductor resonating with a small capacitance, and the combination is resonant at 3579545 Hz. The crystal series resonance in itself is then a few hundred Hz different from the correct frequency. Common values for the total tuning capacitance would be in the range of 20-30 picofarads. The value of capacitance for which the crystal is tuned is specified in a manufacturer's part drawing, but not in service literature. Generally, crystals made for different values of capacitance can be substituted because in most cases the oscillator center frequency can still be tuned to the correct value; however, the pull-in range and hence the temperature drift will be different than intended.