RCA 21" triage CTC20 CTC16x CTC12

[DavGoodlin]

213G216MU-CTC12B.jpg
As you can see some rust where mice peed on the CTC12B chassis but only destroyed the damper tube socket, the filament keeps going out. All 4 PC boards were spared the . This set was full of nesting material when I got it.

This looks very promising as long as there are no gremlins like the other two chassis. The 12's HV is robust at 25 kV (dark screen) and adjusts easily and so is audio. I can’t get a picture unless I reduce then advance the contrast control and see a momentary flash of a raster. The service switch gave me a fuzzy but solid line that I could verify R-G-B screen controls operated. I pull out my handy “Pomona” CRT adaptor so I could easily measure crt gun voltages, and they looked within 10% of schematic K=335v, G1=190v, G2=615v

It was then, right at bedtime that I noticed a little black wire was missing from the 4.7meg 2w resistor in the HV cage to the CRT socket for the focus anode. It must have been pulled out of the CRT socket, leaving the pin when I initially got the set and immediately cleaned it out 5 years ago.

The CRT socket has two rivets so I can access to solder on some Belden wire rated for 20 kV that of similar size and black insulation like original. I can replace the wire to 6DQ5 cap as well. If this works out, I will do all the electrolytics, they being even older than me

[Electronic M]

Originally Posted by DavGoodlin

Very cool thanks for posting this. I worked at two companies in the 80s that were Defense Contractors and they had a zero-tolerance for any outside radios, players, walkman, etc. I had an uber-expensive HP spectrum analyzer and the receivers we made used headphones, that is all you needed plus an antenna to get FM. Several of us were able to listen to the Iran-Contra hearings on WAMU from DC, then we talked about it in the lunch room. The DCAS guys were the G-men who came in to audit procedures, etc. These guys were in to audit while I was listening to WWDC-101.1 and pretending to work on a receiver, still could not help but laugh up my sleeve at the whole affair, my headphones were plugged into the spectrum analyzer the whole time.

My Tek-516 is huge and the RCA WO-91 is just a bit tricky to measure voltage, but the Hitachi scope is fast and portable. Is this what you do at work if "TV sets" are not permitted?
I bought it from the son of a repairman from RI. He lives above my storage garage and one day showed all this stuff of his Dad's he was trying to sell on Ebay. I made a fair offer and got the scope, a Lafayette signal generator and some RC sub boxes.

A friend of mine works at a defense contractor it's easier for him to listen to 8-tracks than any other format. Since most machines especially the one he uses can't record. CDs, MP3s cellphone media playback fuggedaboutit.

[JohnCT]

Originally Posted by DavGoodlin

It was then, right at bedtime that I noticed a little black wire was missing from the 4.7meg 2w resistor in the HV cage to the CRT socket for the focus anode. It must have been pulled out of the CRT socket, leaving the pin when I initially got the set and immediately cleaned it out 5 years ago.

Wow, that triggered a memory. Back when I was 15 or so, I had an early RCA (15, 16?) that had no picture. It had good HV, all the voltages on the CRT socket were there, and I even put our old RCA scope on it and verified video to the CRT socket (my older brother was schooling me on scopes and things). I told my dad that I thought the picture tube was bad. He laughed and told me to change the 2AV2. I then noticed the tube had white residue inside it - hard to see when it had a lovely amber coating of cigarette tar on the outside. The 2AV2 fixed it. Never forgot that lesson.

John

[Yamamaya42]

Originally Posted by JohnCT

Wow, that triggered a memory. Back when I was 15 or so, I had an early RCA (15, 16?) that had no picture. It had good HV, all the voltages on the CRT socket were there, and I even put our old RCA scope on it and verified video to the CRT socket (my older brother was schooling me on scopes and things). I told my dad that I thought the picture tube was bad. He laughed and told me to change the 2AV2. I then noticed the tube had white residue inside it - hard to see when it had a lovely amber coating of cigarette tar on the outside. The 2AV2 fixed it. Never forgot that lesson.

John

the 2AV2 is used in the CTC-16XL not the others like the 15 or 16.

[DavGoodlin]

The contrast control was open, allowing the 12BY7 cathode to rise to 40 volts DC, cutting it off. Part #112840 I could easily order another from Moyer's, but found a 368 ohm with same shaft in my "stash" that even had the tap when the original did not. Ill end up placing an order for something before this is over.

Now I have a raster, can get chroma lock with hum bar and poor vertical sync. The next step is a full recap, CTC12 chassis has a similar problem to the other two and I just need to bite the bullet and recap.


I was also working on this set Saturday night during the Zoom with ETF with my video on.
Steve, Mr. Mike and everyone else made it the most interesting thing "on" that night!

[JohnCT]

Originally Posted by Yamamaya42

the 2AV2 is used in the CTC-16XL not the others like the 15 or 16.

1V2, 2AV2... pretty much the same tube. Your Nitpick award is in the mail.

But I **did** forget that the 15 was the lone departure of a long line or RCA color TVs that didn't use some sort of tube focus rectifier.

We used to carry at least six 2AV2s on the truck all the time, but I can't recall changing more than a small handful of the SS rectifier in the 15 series.

John

[Yamamaya42]

Originally Posted by JohnCT

1V2, 2AV2... pretty much the same tube. Your Nitpick award is in the mail.

But I **did** forget that the 15 was the lone departure of a long line or RCA color TVs that didn't use some sort of tube focus rectifier.

We used to carry at least six 2AV2s on the truck all the time, but I can't recall changing more than a small handful of the SS rectifier in the 15 series.

John

The 1V2 has an absolute max heater volt rating of 1.45v and a min of 1.05.

The heater voltage for the 2av2 is, 1.8v +/- 0.27v
and the spec clearly states “ under no circumstances should heater voltage be less than 1.53v or more than 2.07v

And yes, where the may be almost the same tubes, the heater voltages make them unsuitable to be interchangeable, or at least I would never do so, thus the reason I mentioned it.

[dieseljeep]

Originally Posted by Yamamaya42

The 1V2 has an absolute max heater volt rating of 1.45v and a min of 1.05.

The heater voltage for the 2av2 is, 1.8v +/- 0.27v
and the spec clearly states “ under no circumstances should heater voltage be less than 1.53v or more than 2.07v

And yes, where the may be almost the same tubes, the heater voltages make them unsuitable to be interchangeable, or at least I would never do so, thus the reason I mentioned it.

I worked on a CTC16E, that had a 1V2. The filament dropping resistor changed value and couldn't get proper focusing.
I jumpered out the resistor and installed a 2AV2. Problem solved.

[Yamamaya42]

Originally Posted by dieseljeep

I worked on a CTC16E, that had a 1V2. The filament dropping resistor changed value and couldn't get proper focusing.
I jumpered out the resistor and installed a 2AV2. Problem solved.

Or just forgo the differences with them all as I did with my 16XL , and get a plug in SS tube, ECG511 / R-2AV2, less draw on on the FBT helps, even if it's tiny as the heater current.
However, it's been proven that the SS substitute for the HV rectifier will not work, and overheat and burn up, it happened to me, and to shango066 ( as seen in one of his videos ) on a CTC-16.
Not sure why it smokes, but it seems only the good old glass type works.

[JohnCT]

Originally Posted by Yamamaya42

And yes, where the may be almost the same tubes, the heater voltages make them unsuitable to be interchangeable, or at least I would never do so, thus the reason I mentioned it.

You missed the context of the story, which was how a bad focus rectifier tube could eliminate the raster (a fairly non-intuitive cause/effect which is why I related the story from 45 years ago). I put a question mark after CTC 15 or 16 because I wasn't sure which chassis it was, and indeed it wasn't important to the story. I wasn't offering any specific technical advice to someone asking about focus rectifiers, or suggested the 1V2 or 2AV2 would sub for each other. Again, within the context of the story, it's sort of picking nits.

John

[JohnCT]

Originally Posted by Yamamaya42

However, it's been proven that the SS substitute for the HV rectifier will not work, and overheat and burn up, it happened to me, and to shango066 ( as seen in one of his videos ) on a CTC-16.
Not sure why it smokes, but it seems only the good old glass type works.

Strange. I used to use the EDI 3A3 sub towards the end of the tube era and they worked fine (I think it was EDI, it had a brown and black box). I used both the 3A3 and 3AT2. They were nice because the 3A3 subbed the 1V rectifier tubes in B&W TVs as well as offer X-Ray protection, or so they claimed.

When we changed my dad's original sulfide CRT in his CTC11 with a HiLite rare earth tube, it would eat up 3A3s every couple of months (blooming). We put in an EDI 3A3 and lasted a day and failed. We returned it for exchange and the replacement lasted another 5-6 years or so until the replacement picture tube got weak and it was retired for a '77 XL100.

I cannot say with any degree of certainty that I used on in a CTC16 specifically though.


John

[DavGoodlin]

Always like the idea of less flyback load, also glad not to be using the SS version of a 3A3, yet that filament load could have a measurable effect on 6JE6 cathode current.
Very Good point. Its not enough that I use the 128v High Line tap on the power transformer when we run 121-124 v here thanks to a new pole transformer- not an option on CTC11 and older chassis tho.

[Yamamaya42]

Both shango066 and I tried the NTE508 / SK3756 version and they both fried, mine in 90 seconds, his in about an hour, who knows, perhaps a real EDI 3A3 sub would have worked, but they be hard to find.

[Yamamaya42]

This does however bring up a question that I have tossing with for a while, should the FBT in my 16LX ever fail beyond repair, I do have a replacement for it, but it's not a FBT for an XL, but an NOS one for a CTC-16, which is vertically identical, save for the heater windings/ voltages, since I have a SS focus tube, that won't matter, it will be unhooked, but the HV rect, add a 2.4 ohm res and use a 3A3? Or hook direct and keep using a 3CA3?

Of course, this is all moot, if the FBT in there now never dies!

[JohnCT]

Originally Posted by Yamamaya42

Both shango066 and I tried the NTE508 / SK3756 version and they both fried, mine in 90 seconds, his in about an hour, who knows, perhaps a real EDI 3A3 sub would have worked, but they be hard to find.

That makes me wonder if the ECG and SKs weren't sourced from the same company not named EDI. Other than the one bad SS EDI in my dad's TV, I sold a few dozen (not a big sample I agree) and can't remember any problems. I also sold a few dampers as I recall with no callbacks.

I may still have one somewhere in storage. If I run across it, I'll take a pic of it or you can have it for experimentation.

In retrospect though, I wonder how a shorted SS rectifier would affect the fly. If a 3A3 goes bad, they only go inert. Maybe a SS rectifier isn't a great idea.

John