kamakiri's CTC16

[drh4683]

This is the ctc16 that kamakiri had. It was built late in 1964 but being a ctc16, its a 65 model year. Got it a couple days ago. Had some problems, no vertical sweep, horizontal shrinking and color sync issues.
Got it all fixed up this evening to 100%, some voltage tests indicated no plate voltage on the vertical oscillator. Traced down to an open 1000ohm 3W resistor in the vertical B+. Got the vertical sweep back but then had severe horizontal shrinking which was traced to a high resistance short in the 80uf 450V filter cap. The result of this short resulted in about 120 volt loss in the B+ to the horizontal output thus dramatically reducing the horizontal drive voltage to -30v, supposed to be -56v! The flyback looks perfect yet, not even a drip of was in the cage and its the original! The set definitly got many years of use. Had to fix a few cracked solder joints on the deflection board to cure some "jittering" issues.
The easiest part was changing many tubes! The ctc16 uses 2 6GH8's which were bad of course and a defective 6JU8 color AFC, which you can always count on being shorted.
After the repairs the tv was aligned, horizontal efficiancy, HV etc. Focus balances in the mid of its rotation with outstanding results. Once again, another RCA with that razor sharp color picture!

[captainmoody]

Nice job Doug!
Is the original crt still in it? It looks like the RCA serial number tag on the left side.

[jshorva65]

Nice job!!! The picture on that set looks better than I get with the '90 Magnavox 25" set in my home theater system and the '90 RCA 20" in the bedroom. Now if I could just find a couple of roundie models with remote, I'd be all set.

It would be a fairly simple matter to make a 4.5 MHz "pickup" coil with no actual connection to the set and build an all-tube outboard 4.5 MHz SIF, Detector and MTS decoder based on a modified FM-MPX design and connect that via RCA jacks to my surround receiver. The main differences between MTS and FM-MPX are the pilot/subcarrier frequencies and the dbx NR applied to the L-R component of MTS, which can be convincingly "cheated" with dynamic range expansion to undo the compression which is the most noticeable component of the dbx format. There was a solid-state unit described in a late-80s Popular Electronics that did exactly that ... accepted a 4.5 MHz input and produced stereo output with a cheapie dbx workaround. There's a tube MPX decoder circuit in RCA's RC23 and RC30 tube manuals.

Doug,

Great job, glad its working well for you.

[andy]

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[wa2ise]

It would be a fairly simple matter to make a 4.5 MHz "pickup" coil with no actual connection to the set and build an all-tube outboard 4.5 MHz SIF, Detector and MTS decoder based on a modified FM-MPX design and connect that via RCA jacks to my surround receiver.

I used to be a TV research engineer at the old RCA Smirnoff Lab back when stereo TV sound was developed. One thing RCA found that they had to do was have a separate "video" IF amp that got the signal from a tap on the tuner, bypassing the actual video IF amp. The reason for this was that the true video IF strip had a sloping passband at the picture carrier. This was done because of the vestigal lower sideband carrying the video signal. "Nyquest slope" it was called. Anyway, this slope causes some residual incidential phase modulation mostly from the vertical and horizontal sync pulses to get imposed on the picture carrier and when that is beat against the sound carrier, adds some contamination to the demodulated FM sound. So RCA used a special "video" IF without the slope on the picture carrier to avoid this. This also kept the intercarrier sound system to ease TV station tuning.

So you'll need to build such, or more likely easier to do is use the video IF from a junked B&W TV set, and set the IF transformer slugs to peak at the picture carrier and another peak at the sound carrier. And use the existing 4.5 MHz sound IF amp and detector. At this point it should sound very clean, no buzz. Remove the FM deemhasis RC circuit and feed the audio with MPX signal to your stereo decoder.

[jshorva65]

wa2ise: So there are actually two parallel VIF strips operating at the same frequencies but with differently-shaped responses in stereo RCA models? I haven't done much transistor-tv work in years. Interesting background on newer the RCA designs.

[wa2ise]

So there are actually two parallel VIF strips operating at the same frequencies but with differently-shaped responses in stereo RCA models?

Yes, at least back in 1984 to 87 or so. I haven't looked to see what they did after that (GE bought RCA and raped and pillaged the Lab and I got rif-ed). Other manufacturers used SAw filters with two outputs, one for the video VIF and the other VIF for the sound. Same freqs but different responses. IF amps are cheap now, just an IC then and now.

A tube VIF for sound would not need as many stages of gain like a tube color TV VIF for video would need. You might be able to do a "Madman Muntz" cost reduced VIF for the sound, as you can get the gain up with peaking on the picture carrier and the sound carrier and ignoring the rest of the bandwidth of the TV channel.