Ctc-7aa

[miniman82]

Lookin good!

[IsthmusTV]

I finally had time to attempt a complete purity, convergence and gray scale set up. The picture has dramatically improved. I still need to work on the convergence:






I need to track down the source of intermittent brightness and contrast fluctuations which go away after the set has been on an hour or so. I suspect a tube socket or dirty ground connections.

Also, the image tends to smear a bit (if that's the right term for it), particularly with text. Does this point to an IF problem?


I managed to remove the safety class for cleaning. Of course, I found the VK thread on this AFTER I struggled with mine Fortunately, I didn't damage anything.

I still need to get after the seller about looking for the missing back, but I'm not optimistic that he'll find it so I'll probably be in the market for one. What do they look like? Are they metal, like the rest of the cabinet, or fiber? If someone has a photo of one that they could post, I'd really appreciate it.

That's the update for now. I'm typing this for the second time, since my first attempt mysteriously vanished

-Clark

[wkand]

Really nice job!!!!

One thing I either noticed, or missed, is no discussion of the wax ooze from the fly. Have you checked the HOT cathode current yet? If it's OK, do you have any plans to deal with that?

Is it a problem to have that much wax outside the fly?

[ChrisW6ATV]

Nice pictures on that set.

A CTC-7 back is fiberboard with a cardboard squarish box for the CRT neck. If you have seen a CTC-5 back, the CTC-7 seems similar to me. Mine would be hard to get into a picture, but if no one else posts one for you, I could do so.

[Phil Nelson]

The back on mine happened to be off, so I snapped a photo. It's perforated metal with a cardboard box for the CRT neck.



Other cabinets might have different backs, for all I know. This is the Pensbury cabinet.



Regarding the oscillator tube that tested OK but didn't oscillate, I've had the same experience. An emission type tube tester like mine can't check whether a tube oscillates correctly. I don't know if any tester can. I have seen service books that tell you to keep swapping oscillator tubes until you find one that works.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[IsthmusTV]

Hi Phil, Chris ans wkand,

Thanks for the photo of the back and the other feedback. At least now I know what I'm looking for.

wkand, your question prompted me to finally measure the HOT current. I wasn't too worried about the wax, because the fly only gets warm after a couple of hours. So today I did finally measure the current. The reason I delayed, is that I wasn't sure if I'd have to rig up extension cables. As it turns out, it was really easy to just pull the chassis part way out to gain access to the base of the HOT. Initially, it measured 178 ma, but I was able to adjust it to about 175 ma. I get a nice, distinct dip in the current when adjusting the horizontal efficiency coil, unlike my 1968 Zenith which has a very indistinct dip:


I tweaked the horizontal drive, which maxed out at about 180 ma. It's now about 2/3 clockwise with no signs of drive lines (and gives me 175 ma cathode current).

I'm really enjoying learning about these old beasts!

Thanks again for all the help.

-Clark

[miniman82]

Don't read it with the current function on the meter, it'll give you bogus readings. Put either a 1 or 10 ohm resistor on the cathode and read for voltage instead, depending on which scale you want to read. I had to learn that the hard way.

[old_coot88]

Originally Posted by miniman82

Don't read it with the current function on the meter, it'll give you bogus readings.

Or use an analog meter if you have one. Digitals tend to go nuts on a complex waveform.

[ChrisW6ATV]

Originally Posted by Phil Nelson

The back on mine happened to be off, so I snapped a photo. It's perforated metal with a cardboard box for the CRT neck.

Maybe mine is metal too, and I just spaced out. I do know I need a couple of those clips that RCA used at least into the 1970s on their backs. Mine should have three, I think, but has only one now.

[IsthmusTV]

Originally Posted by old_coot88

Or use an analog meter if you have one. Digitals tend to go nuts on a complex waveform.

Yah, I thought about that after the fact. I do have several analog meters so I'll remeasure with one of those or try Nick's method. I was actually surprised at how well behaved the digital multimeter was for this test. Of course, that doesn't mean it was accurate I did follow RCA's instructions and place a .47 uF cap from pin 3 to ground for the measurement.

And Chris and Phil, thanks again for info on the back. My cabinet style is the "Abington." Phil, the back from your Pensbury looks like the right one. My guess is that it will be pretty tough to find one if the PO comes up empty handed.

-Clark

[Steve D.]

Originally Posted by Steve D.

I believe the CTC-7AA is the late production Abington 21-CD-872-5,
Mahogany Grain Finish CTC7AA, 1958. Hope you can shed some real light on this set and get the owner to part with it. If he does, have him do a search for the back.

-Steve D.

Clark,

As I originally suggested it is the CTC-7 Abington model w/wood grain photo finish on metal. The late production CTC7 Meredith model had the all black (Ebony) on metal finish. Very similar set. I believe the Meredith sold for a few dollars less and replaced the Abington as RCA's price leader model. You should post on all the color/TV forums for a CTC-7 back ie: VK. ARF, ETF classified and any others you can think of. I believe the backs were very similar for all CTC-7 models. As the back covered only the chassis portion of the cabinet which is the same width in all cabinet styles such as Phil's Pensbury. Speaker porions in lo-boy consoles were covered w/thick fiberboard. As an option, perforated metal sheets are available at most big box home centers and can be cut to match the spec. needed for your set and then painted black. Also perforated fiberboard sheets could be used.

-Steve D.

[ChrisW6ATV]

I went and checked, and my CTC-7 does have a metal back probably the same as Phil's. Mine is a CTC-7AK Southbridge. It is on the list of projects here.

[miniman82]

My Anderson has a metal back.

[IsthmusTV]

Thanks for confirming that the backs are all the same. And Steve, you nailed the ID on the set right from the start. I'm going to urge the seller to look again for the back (or let me look) before I post want ads for one. His shop is huge and he's got stuff stored in several buildings, so the original back may be in there somewhere.

-Clark

[Phil Nelson]

I'd go there to look in person, or at least email him a photo of the back cover. To a non-TV person, that loose back might look like a piece of anonymous junk.

Phil Nelson