Director 21 resto begins....
 

This weekend, I began on what's sure to be a long resto on the CTC-4B chassis I hauled home from Indy. Why long? This set was apparently in operation in the same household from the time it was purchased until at least 1976, as evidenced by the repair tags left by RCA techs over the years. There are some ugly looking hack repairs, which will need undoing if it's ever gonna work again. CRT it had was a factory rebuilt 21AXP22, date code says 6543- which seems kinda odd. I would have thought they would've replaced it with a 21CYP22, but apparently the factory rebuilt metal tubes for a long time after they were 'out of service'.

First thing I did to the chassis was wipe most of the dust off, and test the tubes it had. All of them are good, so I won't have to worry about them. First thing I noticed was the power input jack was destroyed, so it will need to be replaced. Looked like the cord had melted to it, but the power trans ohms out fine (crossed fingers for the PTX). Next, I turned my attention to the HV cage. Looked good at first, but a second look revealed a burn under the horiz centering pot and a blown capacitor. Some past tech had wired the (replacement?) caps in totally wrong, which lead to the pot smoking. It will need to be replaced with a new one. Other than that, the horiz output transformer looks brand new so I hope the pot is the only trouble I have with the HV section.

Next, I pulled a few of the can caps and started restuffing them. They will have all new caps installed inside the old cans, then I'll reinstall the cardboard covers so it looks factory. After the rest of the power supply caps are replaced, I'm going to go ahead with a cursory run of the chassis to see what's alive at this point. I'll bring it up slow with the variac, and if nothing blows I'll probably recap the horizontal section so I can tell if HV is good to go.

More after next weekend! :thmbsp:

More pics.

Some guys get to have all the fun!

This'll keep you off the streets for a while! Keep us up on progress. Do you know the CRT condition? Can lend you the tester if you need it (after Thanksgiving).

Yes, fun... that is, if you like long nights slaving over a hot soldering iron as I do! :D

It is always possible that you have a leak somwhere at the glass/metal union, however the work that John Folsom and I have done with leak testing suggests that the more likely point of leakage is the weld that joins the front and rear sections of the crt. In that case it is not likely that frit glass would be of much use in sealing the leak. Frit glass is used to seal the leaks on the glass/metal or glass/glass joints.

There is also the possibility that your 21AX has a leak on one of the leads at the gun end, but a weld leak is more likely. By the time they started making 21AX crt's, the technique of bonding glass to metal cone crt components, was very well perfected. It is likely that there was a small weld leak in the tube before RCA rebuilt it. RCA probably saw silver getters on the dud, and figured the dud was air tight, and so they went ahead and rebuilt it. The leak is so small that even today your getters are still silver, but it only takes a very tiny leak to let enough air into a crt to destroy it. After RCA rebuilt your tube it likely worked fine for quite a while until enough air got in to prevent it from working.

John Folsom and I are in the process of getting our used helium leak detector up and running which will allow us to pinpoint where the vacuum leaks are. Then we will need to proceed with a process to repair weld leaks. Progress has been slow, so don't hold your breath. Hopefully some day we will be able to repair the leakers and have them rebuilt.

That's great news!

What's the deal with welding the funnel, is it a heat issue or the type of metal? And you're right, from what I can see there's still a getter there. I take it the leaks are too small to be found by traditional means (like dye inspection)?

Yep, sad to look at the thing and know it doesn't work. I have 2 like it, one which may have taken many years to develop a low level of air, and the other (in Bob's posession for now) that Scotty tried to rebuild, but showed air within a few days.

I am using the "rubber" shield from the 21AX to shield the HV button on the 21FB - can you slip that between your tube and your mounting hardware? Doesn't look elegant, but works, and can still be re-used if I get a good 21AX.

Making a vacuum tight weld is a very tricky and difficult thing to master. On the 21ax it is not so much the heat issue or the material, but making sure that the weld has no porosity. Proper welding takes very accurate temperature control so the heating and cooling of the molten metal is free from porosity. I had a very skilled welder try fixing a 21ax that we leak tested with John Yurkon, and it still leaked after we rewelded it. Originally we thought the material was Kovar, but after we tested it we found no Cobalt, so we now believe it is more likely some sort of nickel stainless. At some point we will probably need to have the metal analyzed so we can obtain the proper filler rod material for the welding processs.



BTW, Waynem your 21ax is in safe keeping :-) I will drag it to ETF next year for you to take home with you.

Interesting.

Can't detect the bad weld via x-ray inspecting either? We use x-ray and dye penetrant inspections in the military all the time to look at welds, check critical aluminum parts for stress cracks, ect.

It would show up the obvious big leaks, but not the nasty slow leaks. Air molecules are pretty small.

John

Perhaps your cause and effect are inverted...
:D

Nice flyback, still looks raw and uncooked!.

That could very well be! :D


Red Raster: Yes, either it's a replacement or these things are easy on FB transformers. It looks brand new, only mark that I can see is some slightly melted wax on one side and it's from rectifier tube heat.

New updates, from this weekend of deer hunting/CTC-4 rebuilding! :D

Didn't bag any deer, though. :tears:


First I went about reinstalling the first round of restuffed power supply caps, which went well. So far all of the cardboard can covers have come off with little or no heat applied, so that's good. At this point I have both caps from the doubler portion done, and one of the others which is in the audio output section. Only 2 more multi-section caps to go, and the power supply is done. (3rd pic is the restuft caps. :thmbsp:

I also cleaned the front of the chassis up, and the results are stunning! Under all the old cad plating there was nice shiny metal waiting to come out, so I went ahead and did the entire front where the controls are. First pic is the nasty state of the chassis before cleaning, second is a shot of the front after a good de-gunking.

Bonus: the tuner appears to be in working order, no stuck shafts or anything. Even the cords are in good shape, so it looks like a little lube and Deoxit will be all the tuner needs to come back to original glory.

Items for next week: finish the restuffing, do more work cleaning up the chassis, and probably test fire on the variac to see what's still alive!

Nice, tidy work on those caps. What did you use on the chassis?

Phil

First I tried to wipe the crud off with solvent and a rag, which didn't get me anywhere. Then I grabbed a piece of 0000 steel wool, which removed the crap and polished the surface at the same time. You have to be gentle with it though, or it will leave scratches.

First Signs Of Life!!!!
 

Time for another update!



This weekend began much like the last, lots of hunting and not a single sign of any deer whatsoever. In fact, the only deer we ever saw was an already dead one in the back of a fellow hunter's truckbed. All that freezing for nothing, I guess. :thumbsdn:



Fast forward a few hours, and I went on down to the basement to get more work done to the chassis. I finished restuffing the last power supply capacitors, so they all have brand new caps living inside the original paper tubes now. I made sure to use plenty of adhesive, to keep them from bouncing around and possibly shorting. As soon as the glue had set enough to reposition the chassis, I flipped it up, double checked all my work by bouncing it off the schematic, and cautiously applied power for the first time through a heavy 20 ohm resistor in case the PTX was bad (variac is currently OOC).

Nothing happened at first- was the PTX actually bad? No, both fuses were blown. I replaced them with their rated values and tried again. Success this time! :banana: I got B+ (380) and B++ (285), within 20 VDC of the values given in schematic. -20 VDC also looked good, if a few volts high. All tube filaments lit up, so that tells me the PTX is 100% good to go.

Just for kicks, I scoped the horizontal oscillator to see if anything besides the power supply was alive at this point. I was pleasently surprised to find a perfect waveform at the grid terminal of the HOT! Picture of the waveform is below.

All in all, not a bad day!

More!
 

I was not content to stop at having a waveform, as the next day dawned. Something about finding life in a 56 year old chassis gets me going, call me crazy. So after finding the horizontal oscillator working, I decided to pump as many new caps as I could find into critical circuits to see what else I could get. I ended up doing everything on the 2 PCB's, everything in the vertical oscillator, everything in the horizontal oscillator, and a few other random caps just to exhaust my supply. I'm now totally out of .047's, .022's, .01's, and the 'lytic bin took a good hit as well. :D

Turns out the vertical section is just fine as well, though the 6AQ5 running the show tests barely into the green scale on the tube tester. I'll have to get a fresh one before attempting to run a CRT. As you can see in the first 2 pics, I did a whole lot of recapping. Took me the better part of the day to get to this point, my back is killing me. I'm way ahead of the power curve as a result though, I figure there's only about 2 more days of recapping to the matrix section (3rd pic), and the chassis will be 100% free of PIO's.

Tidbit: every single paper cap in this chassis was made by Dumont...strange? :scratch2:
Most were MicaMold labeled made by Dumont, a few were were Aerovox and 'MicoMould'. I left the ElMenco micas in place, as every one I tested was within tolerance. I'll probably get to those at a later date, when I'm not so tired of capacitors.

The one bad part I found so far was a video peaking coil that had split it's case all the way around. The wires inside were eaten by corrosion, so it's toast. If I can't get another one, I'll have to wind one with the help of my brother.

Bad Tubes!
 

Last day of work to the CTC-4 for this weekend. I decided that after the success of getting both oscillators up and running, I should go for broke and see if I couldn't get some HV flowing.

I wired some 10-meg power resistors from the HV tower to ground as a load, and let 'er rip.....


Nothing. Not only did I not have any HV, but the previously observed waveform at the HOT grid was mysteriously gone. :scratch2:

I couldn't find anything at all wrong with the horizontal oscillator, then I pulled the HOT and damper out. Come to find, the HOT had a short which shunted the grid to ground, which explained the loss of a drive signal. I don't have any spare 6CB5's around, so I subbed in a 6CD6 for testing (not same ratings, I know!). Still nothing. Tested the 6AU4 damper next, and it had 0 emission. I was beginning to think the HV transformer was bad at this point, since both tubes that run it had gone bad...dramatically, as it turns out.

In the pic, you can see what's left of the 6CB5 HOT. It burned a hole right through the plate on both sides! Cathode was done for too, and the grids were melted. :yikes:

But my fears were proved wrong about the HV transformer. I put a new 6AU4 in along with the 6CD6, and while the 6CD6 did not like being put in the position of having it's ratings exceeded, it did drive the HV transformer for long enough to let me know HV was working. I saw the normal blue glow from the 3A3 rectifier as HV came up strong, and the power resistors got nice and toasty after a short run. I'd call this a very productive weekend, all in all.

So to 'recap' recent events (pardon the pun!):

I now have a redone power supply, 2 good oscillators, good HV, and all that remains is the matrix recapping before I can take this thing on it's maiden voyage with a real picture tube! Nothing but excitement on my end! :music:

I hate to tell you, but you also let the vacuum out of that 6CB5 :D

Really, great progress! Keep us informed.

miniman82-

Do you have a color TV test jig? If you do, and you need the details of how to hook up your CTC-4 chassis to it, let me know.

Chris,

I have the Sylvania check-a-color with a butt ton of adapters, but nothing for 70* picture tubes or early RCA chassis. I suppose I should cannibalize the NOS brightener I got off Ebay and make my own harness, but I just figured I bring a spare 21CYP22 with me next time I head home for tetsting purposes. Do you have wiring diagrams on how to hook up the check-a-color?

That's whutcha call a sacrificial anode (and cathode too):
http://videokarma.org/attachment.php...5&d=1290924895

:D
Bill(oc)

I have given up steel wool for fear of spreading tiny metal hairs all over. The plastic sanding pads used for refinishing are a pretty good substitute.

Phil Nelson

I haven't had a problem yet, I just blow off the chassis with compressed air and that gets the whiskers out.

I'd be worried about tiny metal whiskers getting inside wafer tube sockets and such. So I'd avoid steel wool. I even hate to have to drill holes in metal chassises for fear of the chips getting into somewhere.

I'm not superstitious, it'll be fine. :p

Yes, I do have the setup guide for my jig, also a Sylvania (CK3000). The guide only covers CTC-7 and later RCA roundies, but I figured out how to make a yoke adapter for the CTC-4 and CTC-5 using another adapter I had a duplicate of. I will pull out my information and send you a message, or post it here, in the next couple of days or so.

OK, thanks for that!

Meantime, Allied Electronics dropped off an early Christmas present today for the '4. Plenty of new caps, the new horizontal centering pot (2-watt wire wound), various 'lytics and so forth. :D

Still on the way is a pair of 6CB5A's, a pair of 6AU4GTA's, a 6AQ5 and a 3A3 rectifier. Those are coming from Antique Electronics Supply, should be here Friday or Saturday. :banana:

I've seen that 6AQ5 cause lots of odd problems in convergence issues if it is gassy.

Your set will be a real sweetie when you get done.

I don't think it's gassy or anything, just reads weak on the tube tester.

The fix is in now anyway, new tubes from AES have arrived! :banana:

NOS RCA 6AQ5, GE 3A3, Dumont/GE 6AU4 dampers, and a nice pair of Amperex 6CB5A's with black plates. Should make for a stout high voltage section. :yes:

Just found out after some resistance checks that the screen/grid control pots are bad, with some intermittent places on the carbon track. Been looking around on the net for replacements, but all I'm finding are crappy quality ones that probably wouldn't last long considering they have boost voltage running through them. Anyone got a good lead on a quality replacement? I'm looking for 5 1-meg linear pots total, preferably with plastic shafts.

You could try contacting Mark Oppat, http://www.oldradioparts.net/controls.html .

Phil

Sent him an email, thanks for the tip!

What's the RCA part numbers? How do they mount? bushing with nut or tabs that twist? I have a stash of (gasp!) GE parts and hundreds of other pots - some NOS Westinghouse stuff from JCPenny's/Penncrest replacement stock.

Trying to help,

They are twist-lock, with a tab on either side of the plastic shaft. RCA part number on the back is 972137-1, but I'm not really concerned about brand. I just want something that's not going to break 2 months from now, like most of the Chinese stuff is likely to do.

Crisis averted for now, I was able to take each one apart and clean them with contact spray. No idea if it will last, but they seem to be working for now.

OK, latest work has revealed the following:

I thought the horizontal osc was working just fine, but when supplied with a signal with my NTSC gen it refused to lock at the correct frequency. I figured I had some more bad caps, so I made a trip to Chesters. After replacing the rest of the old micas, the problem persisted. I then read out the voltages in the circuit, and every single one was 60 high!

I then had a look at the power supply, where I confirmed that B+ was indeed 60 high (440 vs 385). I'm guessing that selenium rectifiers were grossly ineffecient, because there's no way 5 extra input volts equals an increase that large. Short of always running it on a variac or bucking transformer, I guess I'm looking at dropping it with resistors.

So the question becomes do I get a huge high power wirewound, or insert 2 smaller ones right before the rectifiers?

You need to get bypass the selenium stacks with silicon diodes. Leave the selenium stacks in place for looks, but leave them disconnected.

I don't understand why you would have High B+ using the selenium stacks because they normally will be inefficient and produce lower voltages than the silicon diodes.

AFter installation of the silicon diodes I use some 20 watt wirewounds to reduce the B+ to the correct specified voltage in my sets. I use a 20 watt power rheostat to determin the correct value of fixed resistor use.