Dove right in! Help with RCA 21-D-8628
 

Greetings!

First time poster, and perhaps new obsession with this tank of a television.

I have some experience with antique and vintage telephones, cameras, and a few Edison cylinder phonographs. Television is something that I never really expected to get into, least of all a 1957 RCA corner console 21" black and white tv.

I am learning as I go and while I have learned a great deal, I am just beginning to understand this albatross on my hands.

I will link to some of the pictures that I have posted in other forums looking for help.

Basically...I need to rebuild or find a compatible transformer. Each time I read the schematics for the chassis, I see any number of voltages coming and going to the various components. The transformer is burned up, it would last long enough to start smoking while the tubes warmed up. No surprise why the cord was cut!

I am hell bent to either resurrect this beast, even if I have to (heaven forbid) replace the kinescope with a square ish flat screen and keep the panoramic sound speakers. They sound great of course, RCA.

I have started removing components from the chassis. The old solder is being a real pain in the antenna to remove. I prefer to re-wire, solder, cap, etc., the entire piece. You can see many repairs over the years and some badly laid wire that should be harnessed, or just create a more compacted version of wiring.

I have the field service data booklet that lays everything out, that is a big help. But I am still learning to read it.

Any help would be appreciated! Ask questions and find out quickly what I don't know! I don't mind, just don't tell me to give up; that is something I no longer consider much in my life.

https://imgur.com/gallery/PQzX4jL
https://imgur.com/gallery/VsCpGws
https://imgur.com/gallery/0lauJxJ
https://imgur.com/gallery/Sl7MG5u
https://imgur.com/gallery/rz2qNDr

Caution! Some minor issues can be caused by bundling wires or making them "neat" when the factory did not build them that way. Sweep currents of multiple amperes live with signal currents of millivolts in a TV, and moving wires from their original dress can induce sweep interference into the picture.

As an example, when I worked at Motorola, the assembly line for a given chassis had an approved sample locked in a clear plastic case, and the assemblers were told to duplicate the physical placement of all components and wires. Any question of doing it differently was run past engineering, who would change the sample and write an accompanying official change notice.

You should be able to find a transformer for that unit. Make sure you don't run a new one until you monitor the current from the 5U4 output.

Most TVs of that era used very similar transformers. If you can't find one, one from a junk chassis can be made to work without too much effort. Make sure the one you're subbing has sufficient filament current capability, or you can add a filament transformer in place of the original filament winding. You may have to add a dropping resistor if a replacement transformer has too much B+.

In any case, that's a very unique and handsome console in an era where they often weren't.

Oh, and welcome to Videokarma.

John

Others' opinions may vary, but here's my $.02 worth..

1. Service-wise, those early printed circuit layouts were the worst ever conceived, with the foil side of the boards made inaccessable:yuck::eek: (what were they smokin' to come up with that idea?:saywhat: Musta thought the design was bulletproof and would never need troubleshooting.

2. The newly-introduced small neck CRTs usually died an early death. Before proceeding any further, find someone with a CRT tester to verify that (if by some miracle) the CRT is good.

Good luck with your project. As has been mentioned, there are no points given for "neatness" in the wiring. The factory wiring layout and placement is important for the best performance. This includes which wires are against the chassis and which ones are not.

Your chassis is covered in Sams Photofact #400 folder 4. That gives the voltage and current specs for the power transformer. There is no Merit Sub listed but the Thordarson Catalog lists their 26R127 as a substitute for the RCA part number.

True. Don't have a clue what they were thinking other than having exceptional built-in shielding. I worked on a few when I was a young shaver, and my dad had me tack in the defective part on top of the board. Once the TV was running, he had me remove the circuit board and place the components as the factory did.

One good thing about it was that you had to use more technique than just shotgunning if you wanted a nice neat job. Later on, when RCA went to their "unitized" chassis (no more modules), the technique as described in the service manuals was to cut the defective part off the top of the board and solder a new one in place using the old leads. The reason is that RCA used a conformal coating on the bottom they did not want to be disturbed. I used to install those parts through the board despite RCA's admonition not to.


Another good point that I totally missed.

John

I have a post somewhere on here when I did my 1958 corner tv. It was my 2nd or 3rd tv I did. Took me 2 years to find a good crt close to me (I live in the sticks and didnt want to drive 100 miles), but it now makes a really nice picture and the sound is incredible. I watch westerns on it because of the rounded screen, great sound where I hear every horse sound clearly and love it.

Mine has a hot chassis but I might have the transformer you need here and will look the next day or two on a spare chassis I have that came with the good crt I bought.

I did the cut loop and crimp??? technique on a crapload of parts on the circuit boards. It took a lot of time but was a great learning experience but yes frustrating at times. Dont let it scare you. Yes, they are harder to work on than others for sure.

Loop and crimp is fine as long as it's done quickly so as not to partially melt the solder on the bottom of the board a bit. In fact, loop and crimp is overkill for durability.

Years ago I helped a guy work on an old tube guitar amp, and the sockets were brittle. Rather than risking having the metal terminal break flush at the tube socket, I cut a paper cap off the tube socket about half an inch away from the socket and laid the new part *right along side*, so they overlapped that half an inch, then soldered then together.

The guy howled a bit until I explained that parts contained on circuit boards are *only* attached by solder, and not nearly as much solder as the overlapped part had. He saw the light.

John

I don't know what the cut, loop, and crimp technique is; can you elaborate?

As to the transformer, that would be tremendous! I was thinking about rebuilding it; and, it may be worth it in the end just for the experience. I don't expect it to work once I am done with it...and since I cracked the original shell I'll have to have it machined somewhere. Not impossible.

I love the speakers, I attached my GE stereo to it and it was probably a bit overloaded on those RCA speakers, but the clarity is incredible. I'm tempted to just leave it connected to some L/C/R leads just to have Panoramic monaural sound coming from my stereo.

I have plenty of pictures of the original wiring, so I will just follow those as guides. Thanks for the heads up!

As to number 2: I purchased an old CRT tester for Color/B&W from eBay. When I run 6.3 volts to the tube heaters I see a near 80% for cathode grid and cathode; if I switch it from quality to leak I don't see the indicator glow for a leak for the cathode. I'm assuming 6.3 volts is the correct test voltage, and it seems that the transformer has a 6.3 volt lead.

On sets where the IF stages are hand wired disturbing the lead dress can ruin the alignment which is not something you want to mess up.

It might be a good idea to find a 5 tube AM radio and make that your first project. The average monochrome TV is 5x as complex as an AM radio but uses similar parts so if you make a mistake Tracing it down from the schematic is much less difficult.

Phill's old radios on the internet has a lot of good beginner info and detailed write ups with pictures of TV and radio restorations he has done.

The original trans is probably shot, but it might not be. If the B+ line in that set has a hard short on it (say from a shorted original lytic cap) and you didn't pull out the 5U4 before power up the trans could just be complaining of the overload.... sometimes if you overload a transformer till it smokes but don't run it too long it will survive, but the odds of that are not high.

Good luck on your project.

Thanks for the welcome!

It is a very unique and handsome tv, I'm hellbent on restoring it so that I can use it the way it deserves.

What is B+, and, what do I need to worry about?

Thanks! I think the transformer itself is shot, the inside (if you look at some of the links above you can see it) has burned more often than just my testing it about 5 times.

I've seen some scary crispy stuff work like new and I've seen some like new stuff DOA. Electricity doesn't care how ugly the path it takes is.

I would try powering the transformer without a load on it and if it don't smoke measure the secondaries (be careful* the plate winding has potentialy leathal voltage and current on it).

* Keep one hand in your back pocket and work on insulated surfaces.

This would be hilarious if after cracking this thing open I find that it works perfectly and I just had a great learning experience. And then I have to flatten and recreate the box that I broke open!

In your schematic, you'll see the 5U4 rectifier tube.

https://i.imgur.com/AoXlB4d.jpg

That, along with the filtering capacitors, is what turns the AC voltage from the transformer secondary to the DC voltage that the TV circuits need. The 281V point on pin 2 of the 5U4 is called B+ voltage.

The term itself is a throwback to the very early radios which were powered by batteries. Radios had "A" batteries, "B" batteries, and "C" batteries.

Why it's important is that any excessive load or short on the secondary of the transformer can cause it to fail. Why your transformer failed is something we don't know right now - it could have been a bad 5U4 or a short or loading down of the 281V B+ line. It also could have just failed on it's own by developing a shorted turn or there could have been a prolonged load on it.

Monitoring the current in the B+ line and monitoring the current on the AC input side is important if we install a new transformer and want to be sure that there is no other problem in the TV chassis that would overheat or otherwise damage the new transformer.

John

I am having trouble with black and red/black lead, when I run ac to them they hum and cause smoke. If I run hot to the red only, I seem to get more accurate readings without hum. It seems there is a short between the primary winding? What else causes a hum with just black and and red/black to black and red on incoming a/c?

You shouldn't be running AC to anything but black & red/black, nowhere else. That's the primary of the xfmr. Do this -

Remove all the tubes except the high voltage rectifier (probably 1B3)*. This removes all loads from the secondaries of the power xfmr. Now run AC to the primary (black & red/black) again. If the xfmr still smokes, it's shot.

*The 1B3's filament runs off the flyback.

It's shot. Smokeup and sizzle with no load and completely disconnected.

99.999% certain it's shot. But just to be 100.00% certain, do this:

On the off chance there's a hard short on the heater (filament) rail, disconnect the brown & brown/black wires so they 'float' free.

On the off chance there's a hard short in the 5U4 socket, disconnect the red & red/green wires* from the socket so they float free. (pins 4 and 6 respectively.)

Apply power to the primary as before. If the xfmr still smokes, 100.00% it's shot.

*Careful. There's normally around 800 - 900 VAC between these two.

My transformer wont work. Voltages are off. But there were some in 1959 that will work so they made similar ones for a few years. The Thordarson one may be easier to find.

The cut loop thing I may have typed/worded/titled wrong. Somewhere on this forum there is a picture in an RCA repair book of how to do it as they recommended it. But for a quick description you crush the capacitor, peel it all apart, and keep as long of a lead as you can, clean it, make a 180 bend, put a 180 bend on new capacitor, squeeze them together and solder. All of this while not causing stress on the board. Its not fun but there are worse jobs. There are quite a few of them if you replace them all as I did. it takes patience which i have. Some people dont. i wouldnt recommend it to anyone with anger issues, lol

It has been disconnected completely for this last test, only power to red/blk and black. It's probably just shorted. Maybe I can I rewind the entire transformer.

http://imgur.com/gallery/GM9GuOi

Here is a view of the transformer winding. "Jim, he's dead!"

Of all the transformers in an old TV, the power transformer is easiest to sub from a donor. You may have to fudge some parts but if you can't find an exact replacement, you can rube up one without a lot of trouble.

John

That is what I was thinking, I just don't know how you all can figure out the other voltages when I only see 280 and 260.

Otherwise I can just mock up several and make a stage/box in which to put them.

Get a Sams manual for the TV, they usually have transformer specs listed.

I showed the transformer specs from Sams back in post #5 of this thread.

There are only two voltages, the B+ supply of 281 and the filament supply. The filament winding is the brown and brown/black is 6.3vac and that won't vary.

The rest of the chassis voltages are based off the 281, which isn't really critical. Most old tube TVs show more B+ than when new because the AC line voltage is a few volts higher generally speaking than it was in the '50s. If your replacement transformer is a bit higher in B+, make sure you restuff your filters with higher voltage caps.

You just want to be sure the replacement transformer's filament winding can handle the current of the tubes in that RCA. More is good, less is bad.

Other than that you want to be sure the donor transformer is used in a 5U4 rectifier TV as opposed to a selenium or silicon rectifier chassis, so try to find a transformer that will put out about 280 -300 volts off the 5U4.

If you find a donor chassis, look at the schematic and it will give you a great idea it will work, or, if you're unsure, post the donor information here.

John

The replacement xfmr also has to have the dedicated 5 V filament winding for the 5U4.

That's in addition to the 6.3 V winding.

If you don't mind not having the 5U4 you could get a transformer without the 5V winding and use a pair of 1N4007s in place of the 5U4. I've been known to make Solid state 5U4 substitutes and use them in sets where the original transformer runs hot to reduce heater load and cool the transformer.

Yet another option, and an excellent one if the supply of 5U4 transformers available to the poster proves scarce. There may be more 1960s transformers laying around than '50s.

I suggested a 5U4 equipped donor by considering the skill level of the poster. A 5U4 transformer would take care of all filaments with just the B+ to tweak and likely a couple of holes to be relocated for mounting.

But something like this RCA, that isn't a historic piece, should be put back into operation even if requires some minor modification.

Looking forward to seeing it run.

John

I found this one that I pulled from a late 50's narrow neck RCA. I kept the Sams page with the transformers specs and Sams lists it as the exact same voltage/current ratings Tim posted. I'm not sure if it will physically mount the same, but there's a possibility. I've checked resistances of the winding's and they look good. If you think it will work send me a pm. USPS flat rate box will be the cheapest shipping method. But before you start investing money I'd recommend you follow Old C's advise and get your CRT tested. Also I might be upset if this transformer also goes up in smoke. ;)

https://live.staticflickr.com/65535/...01a542b8_z.jpg

https://live.staticflickr.com/65535/...b3747e1c_z.jpg

https://live.staticflickr.com/65535/...39f9a663_z.jpg

https://imgur.com/a/yalufGU


Here is a test with the CRT tester I purchased on eBay. Perhaps you all can figure out if the tube is good.

It is probably good. Not sure what the egg timer is for. CRT emission can be asleep for a couple minutes to a couple of hours in some cases but precise timing is not important, all that matters is waiting till emission eventually climbs which it appears to have done.

On all glass CRTs cathode emission is usually the only important metric. (Other defects usually aren't noticable or can be worked around with an isolation "booster" or similar.

Step .1) identify mysterious transformer for possible use.

Hi all,

I took a break to collect information and regroup. I am going tp reinstall all of the original components I removed, it will be good practice for actual replacement. I found a transformer that could potentially have come from an RCA chassis.

I'll post a link to the images, I am trying to identify primary and secondary windings to compare to my KCS116C chassis needs.

I am struggling to identify and measure ohms/volt outputs for needed voltages.

Perhaps the group can help.

Thanks!

Jordan

http://imgur.com/a/LNuBET5

The *first* thing I do on an unknown transformer is to check every wire to see what other wires (there is at least one) have continuity.

I then put all wires with resistive relatives into groups. Within each group, the wires that read highest resistance to each other are the outside connections, and the third wire will be the tap.

Note, if you find one wire that has no resistance friends, you have a bad transformer...:tears:

John

Are there 9 leads coming out of the xfmr?

If so, what I would do is this - First identify the center-tapped hv secondary. It'll measure a few hundred ohms. That'll get 3 leads outa the way.

Then identify the 5V and 6V secondaries. Each will read very near zero ohms. Never mind which is which for now.

The remaining winding will be the Primary, and will read a few ohms. Put the juice to the Primary, and measure what voltages you're getting out of the secondaries. Careful - there can be 800 - 900 VAC on the hv secondary.

11 leads I beleive

Probably just another 6V filament winding.