I have mentioned this before but I was a bit unsure. My RCA TCS-127 needs a power transformer. After much hope of this not being the problem I have come to the conclusion that it is. :tears: I borrowed a Megohmmeter and verified that my primary is shorted to ground. Along with at least one secondary winding. I stopped checking after that. I dont know how hard this is going to be to tackle. Not doing the work but getting the replacement part or having the existing part repaired.

Are there places that rebuild iron core transformers?

Are there places that sell N.O.S. or replacement transformers?

I have never had to replace any of my transformers so this is new to me. Any help or advice would be greatly appreciated. Here are the part #s on the trans: 970972-1-3
138012

The chassis # is KC534B

THANKS :thmbsp:

I would take the covers off the transformer and make sure the insulation on the hook-up leads isn't disintegrated inside...we have repaired some with bad insulation on the wiring by covering the old wire with heatshrink tubing all the way to the core.

If the transformer is really bad places like Radio Daze have general replacements
and on Steves site someone rewinds them and with a old sub book maybe a parts set has one like the 9T246 on Ebay for $20.00??
Item number: 150050438486

Hi. These sets have two line capacitors, and a resistor going to chassis that can fool you. I'd just remove those parts. On secondary, they sometimes had a negative bias supply ending to chassis with a resistor, and a positive secion of an electrolytic on the chassis. You may be actually measuring those two sources.

Bill Cahill

What I did was remove the rectifier. That its self deisconnects 3 leads. Then I removed the two leads going to the small strip with a B+ fuse (I thiink). I removed a lead that goes to one of the filters and I think one that supplies the heater string. I also disconnected the ground side if the line filters. This should have eliminated the short if it were in any of those circuits. I applied AC from the wall and still have a heavy current draw. The transformer hums like it is working its a** off what little time I can leave it on, which is a matter of seconds. The line chord will get hot and there has been a burning smell. I have nearly every indication that the trans is bad.

The megohmmeter does not help as much as I thought. I have compared the readings I get against other sets with known good transformers and they are similar. I was told that I should see no more than around 10M Ohms on the 250v scale and if I saw low readings that would indicate a short. I get nearly the same reading from say either side of the line input to ground. Also I get the same reading from one of the secondary leads going to 5u4 and to ground. The rest seem to be isolated. I will say that the motor tech that loaned me this hand crank megohmmeter is not a television repair man but he is trained decently and spends a lot of time finding shorted field coil windings in electric motors. We thought that a power transformer would not be much different.

Also I have to watch swapping from other sets because I have noticed that even though many RCA chassis use what looks like and many times are the same value components, it is not a given. This ct-127 has a different trans than my 8T-243. Probably the ebay 9T set will have the same one as my 8T. Hopefully something will pop up. On another thread someone said these trans. are pretty common. Hope so!!

What I did was remove the rectifier. That its self deisconnects 3 leads. Then I removed the two leads going to the small strip with a B+ fuse (I thiink). I removed a lead that goes to one of the filters and I think one that supplies the heater string. I also disconnected the ground side if the line filters. This should have eliminated the short if it were in any of those circuits. I applied AC from the wall and still have a heavy current draw. The transformer hums like it is working its a** off what little time I can leave it on, which is a matter of seconds. The line chord will get hot and there has been a burning smell. I have nearly every indication that the trans is bad.



My next step would be to remove the power transformer from the set (but keep track of what lead went where, especially the primary). Once the transformer is removed, I'd try applying line voltage to the primary briefly again to see if the short is still there. Check the insulation of the wire leads; if it looks brittle and crumbly, the short might be there. Carefully remove the end bell the wire leads come from (if you didn't already do that to remove it from the set) and check further, and slip heat shrink insulation on the problem leads. Of course, if the transformer smells like toast, it might be toast, but don't give up easy on it.

If the transformer in the set is drawing so much current that it makes the line cord get hot, I'd wonder about the circuit breakers or fuses in the house. Check that nobody stuck pennies behind the fuses....

I totally agree. I also don't see alot of similarity between motors, and transformers. The transformer sounds very shorted, alright, but, I'd agree you should remove it, and physically check the wiring first. If the transformer is making a bad odor, it probably is burned. I'd also suspect something in your house isn't right, as this should trip a breaker, or blow a fuse. The fuse in the tv is only a boost fuse for hv section. You eliminated one possibility by pulling 5U4's. I think this set uses two, but, I could be wrong.

I still say your filters are shot, and reming you there is usually a resistor from line to chassis as well as the grounding capacirots.

By the way, those two line caps were supposed to eliminate line interference, especially from medical devices, which are not even used any more. In most cases, removing them permanently will not affect the performance of the set, and actually, make ths set electrically safer.

Do now, however, attempt this on a ac dc set with out a transformer, as they are a different animal all together.

If the tube line up is the same as yours, chances are a replacement transformer would be fine. Make sure of every wire on both new, and old one. Colors don't always match.

By the way, it might be safer to put a light in series with the primary of the transformer. Under normal circumstances, you'd need a fairly high wattage, but, for this kind of shorts test, 60-100 watt should be plenty. If butl light full blast, no doubt about it, you have a major short. You obviously do, anyway, just, where is it?
It is a fairly common set, so shouldn't be hard to find the correct transformer for. But, consider this.
What is the physical condition of your set?
What type of cabinet does it have?
Are you really in love with the set?
Are you willing to put what ever it takes into bringing the set back to life?

By the way, there is still the resistor network going from B- to the chassis, and will still show a "short".

In all fairness, I love the old sets myself, but, don't destroy a better one for what you have.. It's a nice set, but, RCA used this chassis in many models. By the way, what is the exact chassis no? It would have a KCS in front of it.

KCS stands for Kinescope chassis set.
If anyone is wondering, The CT in RCA's color line stands for Color Television.

Bill Cahill

I'll try to sum up some things that are on other threads and this thread. When I first got the set naturally I used the 100watt bulb to reduce line voltage. Things seemed very hopeful as the bulb dimmed like it should and the tubes all glowed dimly. Perfect. I only did this for like 3 hours. I probably should have done it all night. This set seemed to be in real good shape so I didnt expect to have major trouble. I found that the LV rectifier was open so I replaced that. Then I applied 110V. That is where my troubles began. Instant major transformer hum and WARMING of the line chord, along with the bad smell. I would say that if I had left it plugged in for more than the 5 or so seconds that I did then the breaker would have took over.

At that point I hoped it was bad electrolytics so I went and bought new ones. I really felt good except for the fact that NONE of the existing caps gave ANY indication of anything that would cause a major draw. A cap that bad should be noticable with an analog ohm meter. Needless to say my second thoughts were right. Plugged her in and had exactly the same problem. That leads up to my using the Megohmmeter from work this weekend and pretty much determined that my primary winding is shorted to ground. The needle pegs when you crank the generator. I get the same effect from one of the secondary leads to ground. My wires are in great shape. Sounds pretty shorted. The transformer does not have RCA painted on it like my old 8T-243. Instead the #'s are stamped into the housing. Maybe the factory was trying to save a buck.

As far as the set being worth it. Yes! I have been wanting a roundie with a double d mask for ever. Not a lot around my area. Most people say the first TVs were in town around 1952. Many sets I read about have the 10BP4 like my 8T-243. This set has a larger tube. I forget the exact size. That makes it kind of unique to me. I love the doors as well. I would say the set shows average wear and tear but polishes up very pretty. Also, it has a rebuilt GE crt which is a positive aspect I think. It was installed in the 60's so it may not have much time on it. Such sets pretty much retired through the 70's. Thats how I gained interest as a kid. They were still siting in the corners of local repair shops and easily obtained cheap or free. Some 50's sets were in my high school electronics shop. That was cool. Even a Predicta that I would tinker with. Nobody cared about the older junk. We now had SOLID STATE!!

Hopefully this set will come together well. I want to reduce my collection to some degree and focus on a select few favorites. I really hate getting rid of anything. Y'all know how it is. I still have a late 50's Montgomert Ward's Airline for free if anyone can pick up....

Hmm. Sounds like it's worth saving. I wonder if this is a 16" set?
I have the power transformer from one of the early 16" sets. It has bad leads,but, I think transformer is still good. Can you get me the chassis no, and a good picture of the back of the set? Thanks. Bill Cahill

Thanks Bill, the chassis # is KCS34B. The c.r.t. is a 12LP4. I don't have a pic of the chassis as we speak but I may get one soon. You seem to be familiar with the old RCA's. Well I'm not as familliar but got some experience working with the "ugly" 8T-243 that I have mentioned and the chassis seem to LOOK identical. Really it LOOKs as if I could trade c.r.t.'s and swap chassis if I wanted to. I suspect there are some component value differences. I really don't want to change the subject to chassis swaps. Right now power supplies are the issue. My 8T had power supply problems as well but they were cured with caps. Not so with this TC-127.

How much difference is the desirablilty in relation to c.r.t. size, if any? It just seems like every other set mentioned has a 10BP4. I know that is a common tube. Again my 12LP4 is a G-E rebuilt with no brightener so I think I am good to go there. I know it would be smart to find out before getting all involved in restoration but unfortunately my tube tester all works fine, exept the c.r.t. test. It used to work fine and suddenly stopped. Sometimes I think it is crazy to use diagnostic equipment that may need as much diagnosis as the repair job......

The megohmmeter does not help as much as I thought. I have compared the readings I get against other sets with known good transformers and they are similar. I was told that I should see no more than around 10M Ohms on the 250v scale and if I saw low readings that would indicate a short.

I not sure just how much voltage the megohm-meter is putting on the wiring. Are you sure it isn't more than the insulation can take?

If you have a short that is causing the transformer to pull enough current to cause the line cord to heat up you should be able to measure that easily with a standard ohm-meter.

This may give you and idea of what you should see on the different windings resistance wise: http://www.radioremembered.org/xfmr.htm

Glad you're gonna save it. An early RCA with a newer CRT is a recipe for an excellent picture. :yes:

Please try what the others suggested and disconnect it. Test it on the bench. The forums over on antiqueradios.com are full of old threads where someone was convinced the transformer was shorted, and the problem disappeared when the transformer was totally disconnected. Shorted tube sockets, dial lamp sockets, and such. I'll admit what you said sounds really bad for the transformer, but humor us and try it. If it's bad, it's gotta come out anyway.

Even if it's bad you still might fix it by replacing the insulation under the end bells like Chad suggested.

I don't have a crank megger. I use a HV power supply and a VTVM. You don't happen to have these two items, do you? I suspect this is doing exactly the same thing as your megger anyway. If you have this stuff laying around, post back, I'll tell you how.

Ok, if it *is* toast, I don't know of anyone rewinding, but I've heard Heyboer will make you new transformers to original size and specs. This might be a good option if a universal one wont do for some reason, or you want an exact fit.

Good luck,

John

The good news is I have a KCS 34B. The bad news is I might need it's transformer. I picked up a T-120 that someone has messed up the power suppyly, replaced power transformer with possibly the wrong one, then, wired it wrong.I still have to check. However, I do have an extra one with bad wires,that I believe is not toast. It's a commontrhasformer in RCA's, and was used on a number of chassis'. Voltages, approx., follow:

Pri. 117volts ac. 50-60hz. Hv. Winding. 730volts AC Center tapped.
Sec.2 5volts AC 4 A.
Sec. 3 6.3 AC. I belive that one is 11A.
Sec. 4. 6.3 AC 2A insulated for 1200 volts. This fil. alone is used for the 6W4 fil. , which is not grounded, as it is connected to cathode to cut back on danger of arcing. Never ground this, or connect it with other filaments, as I guarantee it WILL cause major dammage.

If I am wrong about that winding, and your damper tube just happens to be a 5V4 The fil. specs follows: 5.0volts, 3A. Insulated for 1200 volts. On our inflated ac voltage of 120-124volts ac, The voltages will be somewhat higher.

I hope this helps.
Bill Cahill :banana:

How much difference is the desirablilty in relation to c.r.t. size, if any? It just seems like every other set mentioned has a 10BP4. I know that is a common tube. Again my 12LP4 is a G-E rebuilt with no brightener so I think I am good to go there. I know it would be smart to find out before getting all involved in restoration but unfortunately my tube tester all works fine, exept the c.r.t. test. It used to work fine and suddenly stopped. Sometimes I think it is crazy to use diagnostic equipment that may need as much diagnosis as the repair job......

Generally with early sets the smaller the screen size the more desirable the set. 12" isn't far from the standard 10" and is still very desirable. Really, any round tube sets are. When you start getting into rectangular tubes the interest starts to fade.

To Chimes, I'm not sure how much voltage the megohmmeter puts out either. The guy that loaned it to me said something about 4 times the operating voltage. He could have meant that the meter puts out 4x or that is what I needed. There were three ranges, 200v, 600v, and 1000v. I used the 200v. I seriously doubt that the momentary spike would damage anything. Nothing got hot. Also thanks for the link! Everyone should be able to use that info. I find the color coding confusing as my transformer does not seem to follow suit with what they show.

To Bill, no I don't have the items you mentioned. However I feel like simple resistance readings should tell the tale of a major short like I have. I should not have resistance readings from disconnected wires to ground in places I am getting them. A few minutes ago I took some readings. Here are some examples. These checks are to ground. Pin 4/5U4=1,300 ohms, pin 6=1294 ohms, the lead that goes to the switch has 91,000 ohms. I get 1.8 ohms across the ac line with the filters disconnected. Thanks Bill!!

To Bryan, I kind of knew round was better but I wasnt sure about size. I know any of us would like to have one of those huge DuMont Royal Sovereign sets with some ridiculously large crt, so I guess size is not necessarily a rule of thumb. Also I have a couple of the 50s rectangulars that I know are good finds. I always thought that interest started falling off around the early 60s with old TVs. The early Color sets then take over. There really are no guidelines as the hobby has expanded somewhat and there are some who find 70's stuff interesting. Some of this is relative to a persons age if you think about it. One day someone may find nostalgia in the plastic junk Walmart calls TV's. Go figure!!

Thanks for the help everyone. Still open to ideas and suggestions....

The way I would do this is to remove the transformer from the chassis, put a 60 watt lamp in series with the primary. Connect to 110 volt ac. No secondary leads connected to anything. Bulb glows bright=short. Remove end bells, check for bad insulation. Bulb glows diim=short somewhere in the chassis wiring.
There can be carbon tracks on a tube socket or some other elusive issue causing a short. It's a waste of time to keep trying to troubleshoot it without completly removing the loads from it.

I don't get into the whole how much is it worth thing but you will often have to spend more to repair something than you could sell it for. That only matters if you're going to sell it, though.

The criteria for collectable sets is pretty much confined to those with round tubes, especially for black & white sets. Post 1951 for black & white and maybe not until after 1960 or so for color is when sets go from truly collectable to merely interesting.

I used the 200v. I seriously doubt that the momentary spike would damage anything. Nothing got hot

I doubt the meg-ohmeter will put out enough current for anything to get hot.


A few minutes ago I took some readings. Here are some examples. These checks are to ground. Pin 4/5U4=1,300 ohms, pin 6=1294 ohms,


This would be the hv windings to center tap. I am assuming the center tap is grounded to chassis. Since both measure within a few ohms of each other they are probably OK.


the lead that goes to the switch has 91,000 ohms.

That should not cause enough current draw to make the line cord heat up.


I get 1.8 ohms across the ac line with the filters disconnected.

That seems a bit low. What filters are disconnected? I would do what chad suggest. Disconnect all secondary leads and see if the problem persists. If so, then there are probably shorted turns in the primary.

Bill H.

" I get 1.8 ohms across the ac line with the filters disconnected."

That seems a bit low. What filters are disconnected? I would do what chad suggest. Disconnect all secondary leads and see if the problem persists. If so, then there are probably shorted turns in the primary.



1.8 ohms isn't outside reason. I just measured the primary of my RCA TV set (it works quite well, other than a weak CRT that wants a brightner to work well) from 1957 and got 2 ohms (using a DVM on ohmmeter mode across the power plug pins with the set's power switch turned "on", which presents to me the transformer primary without having to take the back off the set). The impedance of the primary winding of the power transformer at 60Hz is what limits the current to a lot less than a pure 2 ohm resistor would draw.

What filters are disconnected? I would do what chad suggest. Disconnect all secondary leads and see if the problem persists. If so, then there are probably shorted turns in the primary.Bill H.

ALL DC electrolytics, the two AC line filters, along with everything else are disconnected from circuit. I admit that as I stated before I simply pulled the 5u4, which automatically takes 3 or 4 transformer leads out of circuit. On one pin you have to remove the smaller wire that goes to the filters. I checked for pins shorted to ground. No problems. I also left a lead going to the on/off/volume potentiometer-switch. I checked the switch for short to ground. No problem. There is a lead going to one side of the AC line connection. That is not shorted.

Someone made the point that the transformer will likely end up coming out anyway so why not remove it from the chassis. Good point. I guess I took some "short" cuts while waiting to see if I can secure a direct replacement. Sometimes I take stuff apart and get sidetracked or disgusted and it sits in pieces way to long. Or the pieces may get lost. I shouldnt be able to lose a transformer though.

Again I have a good trans in my old 8t-243 but evidently that set is more "collectable" and it is kind of dumb to scrap a good set to fix another. Also although the chassis are identical there are different part #'s on the two transformers. I don't need to confuse the situation any more with thoughts of swapping.

Thanks to everyone for trying to protect me from hastily going and purchasing a transformer to find out that it was never the problem. Last I still think that there should simply be a resistance measurement that would tell the tale of a large short. Transformer checking has always confused me a bit because you usually don't have a set measurement that you are looking for on the particular transformer. Sometimes the winding resistance is listed on the schematic. The 8t schematic is all I have and it is not listed.

You may find another set that has a bad CRT or cabinet that could serve as a parts set...I haven't found the task of removing a power transfomer from a chassis to be too bad. It's pretty non-destructive so you wouldn't be destroying another chassis to remove the transformer.
I have not used resistance measurements very much as a troubleshooting tool except in cases of components completely removed from the circuit.

Resistance measurements are almost never any good to fault isolate a problem in a power transformer, unless it is an open circuit in a winding.

In the case of a short, usually what happens is adjacent turns in one of the layers in a windings short together. This only reduces the overall resistance of that winding by a fraction of an ohm, which is undetectable. But the effect on the transformer is dramatic. All the power in the transformer is delivered into that one shorted turn. That shorted turn overheats and causes the symptoms you describe. But a short EXTERNAL to the transformer will cause much the same results. You need to unhook ALL the secondary windings of the transformer. For the B+ circuits, this can be accomplished by simply removing the rectifier tube(s). For the filaments, you would need to unsolder at leas one of the wires on each of the filament secondaries.

Once you have done this, apply 115VAC power to the primary, and if the transformer still groans and gets hot, it has an internal short.

ALL DC electrolytics, the two AC line filters, along with everything else are disconnected from circuit.

No need to disconnect the electrolytics, pulling the 5U4 will isolate them.

Someone made the point that the transformer will likely end up coming out anyway so why not remove it from the chassis. Good point.

You shouldn't need to pull the transformer to find the problem. Do as John suggests, that will prove it one way or the other. If it proves bad, then you can remove it.

Great explanation of what happens when a short exists in a transformer John Folsom. Thanks!!

About the DC electrolytics, I guess I said it wrong. I meant that by pulling the LV rectifier I had eliminated the electolytics as a possible cause of the heavy load. Still thanks Chimes for backing up the no need to remove idea.

I think I have a line on a NEW Merit replacement. Wish me luck...........

Well I have the Merit replacement. I am going to need some help from someone who can pinpoint where each secondary leg will go. Reason being the replacement has a different color code. If I had a GOOD schematic I could look at where the various voltages are applied. For now I have no correct schematic. I have a Sams for a similar RCA and it does not show the voltages. The Merit replacement is quite a bit smaller as the end bells are not as tall, but it looks like it mounts up the same. Its a Merit P-0370 and the supplier insured me that it was a direct/drop in replacement. I hope he was right!

Even the way the color code breakdown on the box is confusing. I think it has something to do with the center tap. You can plainly see that black is 117 VAC, Green is 6.3v, yellow is 5v @3A, brown is 6.3v @2.7a. The two reds and the red/yellow say 350-350 vac @ 225 m.a.d.c.

If anyone can help pinpoint my connections and/or verify that this transformer is correct it would be greatly apreciated. Also some explanation of the red and red/yellow wires would be nice. Does this have to do with a "center tap"?

Thanks folks!!

Is your set a KCS-38 chassis?

I assume you mean the two reds are the secondary and the red/yellow is the center tap of the secondary. A center tap is just an wire connected to the mid-point in a winding. For this set, it is the return for the -120V supply. An ohmmeter can verify this, and check all the other windings and verify all the windings are isolated from each other.

The original transformer has a 6.3V 1.2A winding for the damper tube, a 6.3V 9A winding for all other filaments, except the rectifier, which uses a 5V 3A winding.

So I would assume yellow is for your rectifier, brown is for your damper, and green is for the other filaments, though you did not say what its current rating was. It better be close to 9A. If it is something less than 9A, then you can add up all the tube currents from data-sheets to calculate the actual current requirement to see if you green winding provides enough.

Good luck

Hi John, thanks for the info. I think this thing will work out and most of what you said was close to what I had in mind. Yes the green lead is rated at 10A. Now my unit has the Brown damper lead reated at 2.7A. Will thet present a problem? As far as the "two reds" go I mean I have 2 reds and a single red/yellow stripe. I have two of every color.

I measure 1.7 ohms between the blacks, .2 between the greens, .2 between the yellows, 65.2 between the reds, and 34.1/31.2 from either red to a red/yellow.

The chassis is a KCS-34b.

Do you have a schematic for this particular chassis? I already know other models that look the same have diffferent value components. I need to find out exactly where to solder every wire. The damper, rectifier, and other filaments should be simple enough. All of the red or red/yellow still confuses me. I'm asking for quidance because I want to be sure on this and not cause more problems.

Maybe these readings and more info will help you decipher some of this stuff. Efforts greatly apreciated!!!!

Thanks

There should be 3 wires on the b+ winding, and the different one will be the center tap. This is the red,red,red/yel probably. The red-yel will be the center tap.

So, just using the way the old one was hooked up as a guide, hook it up. What I mean by this is that the old one must have also had 2 leads the same and one different. Use this as a guide.

Another way: Hook the two wires that are the same color to the rectifier plates, and the different one where the old third wire was.

John

PM me your address. I am certain that I have a Spare SAMS 93-9 for your set.

polaraman

Tiubejunke,

What blue_lateral said. The two red wires go to your rectifier plates, the red/hello0w to the -120V bus return (where your old transformer denter tap wire went).

I can scan you jpeg images of the RCA schematic next week, but you shoud take polaraman up on his offer to send you a Sams for your set.

Let me know next week if you want me to scan the RCA schematic.

Good luck!

Heres the latest on the TC-127. I finally got around to unbolting the original transformer. I removed the endbells. Now I know where the burning smell came from. No bare wires shorted. Just burnt. Really that is good since I have invested in the Merit P-3070. The Merit unit is a bit smaller which means less weight. That always helps.

There are some differences in specs from the original to the Merit. John said that the original damper winding was 6.3v 1.2a. for instance. The Merit is 6.3v 2.7a. There are other differences but my Merit specs out at more than the original amperage in all cases. I would think that would be OK. Somebody make me feel good on this one.

Since I have real nice cloth wire I am thinking of simply connecting to everything up near the mounting point. I will not have to thread and tuck away new wire if I do this, plus the aspect of a more original apearance. I have to locate a big 2 watt 100 ohm resistor before I fire up the old thing. I noticed one that was cracked in two. Not really burnt, but cracked.

Now that I work a regular 9 to 5 its hard to get to one of the FEW electronics suppliers around here. Too bad Radio (joke) Shack aint what it used to be...

They probably wouldnt know what a resistor is.....Remember buying and testing tubes at the Shack? Those were the days!!

The Merit is 6.3v 2.7a. There are other differences but my Merit specs out at more than the original amperage in all cases. I would think that would be OK. Somebody make me feel good on this one.



Yep, more amps is more better!

Tubejunkie,

The SAMS went out today. I have the same set in storage.


polaraman

Thanks friends. I'm going to start the install tonight.

Just for the sake of conversation here are some resistance measurements from the old (fried) transformer. Pretty weird!!

First I notice that none of the windings are color coded like my replacement. Merit had sense enough to group the windings in code. Like wire colors are seperate windings in this crazy thing. You get infinity across all but yellow to yellow.

Now between the Blue/yellow stripe to a Black I measure .7 ohms, 1.4 on the other set.
Between a Brown and one of the Blue stripes I measure .4 ohms, same on other.
Between one Yellow and a Green stripe I get 9.2, to the other yellow I get 14.2. This is weird because my measurement between the two yellows was 15.2.

I thought I had found the winding with center tap. Actually I probably have but I must remember that I am taking measurements from a faulty unit.

No wonder in the beginning I was having trouble taking resistance measurements. I was trying to match colors as far as windings go. Live and learn....

Well, the replacement bolted in fine. My game plan was to cut the old leads up near the old transformer and using a minimal amount of the replacements wire as it is rubber instead of the better looking cloth. On top of that I think this would be the best way to go in terms of common sense. The replacement did not have enough lead to go to the various connection points, so either way you would have to add some wire. Why not use what is there AND already routed real nice?

So, everything is now wired in. (Hope its all right) I went ahead and purchased enough caps to replace the whole power supply filter section and MOST other electrolytics. I also got a bunch of orange drops to replace most of the wax coated paper caps. Now I see why a lot of pros say change all of the caps. Tonight I noticed a 100 ohn 2 watt resistor burned in two in one of the horizontal circuits. There was a .0022 near by that measured like .012 and also there was a .22 that measured .001. I'm not sure about the mathmatics or exactly how much tollerance is allowed without noticable performance issues, but a measurement is a measurement and that is way off from the new stuff I put in. At least I will have peace of mind. I did not fool with the crazy stripped black caps which I have heard are troublesome as any, if not more. I may regret this move...

I'm trying to do this right so I have not yet applied line voltage to the set. I may break out the 100watt bulb again. I believe you are supposed to pull the horizontal output tube when doing the reduced voltage run. Anybody know?

I should have some results this week. I have a goal of seeing a picture by Christmas. Unless I really screwed up some wiring I should be a winner. Hopefully the power supply was the major problem area back in the sets use. That way all the RF coils and other odd ball things will be ok. No mysteries....

Hopefully!!

Yes you will regret it if you leave those striped caps in, please replace them or you will be asking for trouble...you can end up with hard to diagnose troubles or even if the cap holds together now it will decide to crap out and cause damage when you have it all back together.

Chad is right... change those black caps! All kinds of quirky little problems go away when you get rid of them. Also, I've had those blow out... and it will certainly cause you to soil your britches... they sometimes sound like a 22 pistol going off.

...

Good info.. Thanks folks!! No progress today. I feel like I can try the set with the black caps still in place. Sure there will probably be less than perfect performance but I can kind of check my progress so far with the whole power supply being replaced. Actually I went for a long time leaving those things alone in other sets because of that stupid color code. I have a book now that helps decipher what value thet are. Before that I just changed electrolytics, tubes, and bad resistors.

The sams with the pictorials also makes it easy to verify you have the right value on those black color band caps.

Well, my "by Christmas" goal will not come to pass.:no: I finally plugged it in. First with a 100watt bulb in the line for about one hour. Everything seemed OK. The light slowly dimmed, so I knew my SUPER SHORT days were over. The bad thing about the bulb method is that the voltage is so reduced that the DC never gets pumping enough (or at all?) to slow charge and reform the paper caps. I think it works this way.:scratch2:

Needless to say after a couple minutes of operation with no sound or raster I heard a sizzle:tears:and quickly disconnected the line.:sigh: Low and behold one of those stupid black stripped paper caps had gotten hot. A .018mfd 1000v damper filter. I unsoldered one end of the thing and it measured like .15mfd.:no: So until I get my hands on the 7 or 8 1000v caps that I will purchase to cover everything needed I am at a standstill. I have enough orange drops to keep me busy with the soldering iron. Just no 1000v jobs.

I feel good even though I still have a dead set. I started off with something that could not safely even be plugged in. I may not be as far away from success as it seems. This cap is probably why I never got a raster. Then I can look into getting sound. I didnt expect a much better result. I just wanted to make sure that there were no screw ups with the power supply re-vamp.

IF you get those caps in time, you could set a new goal of "by New Year's" and possibly have a good enough picture to watch the ball drop for 2007. :yes:

...

The bad thing about the bulb method is that the voltage is so reduced that the DC never gets pumping enough (or at all?) to slow charge and reform the paper caps.

Correct. When you "warm start" a piece of tube equipment by variac or series light bulbs, the transformer is operated at reduced voltages. This means the 5V supply to the 5U4 filament is reduced as well. At reduced voltages (especially at the low end of the variac sequence), the 5U4 filament isn't hot enough to "boil" any electrons, the electron cloud is not present, the plates do not conduct at all (no emission). You'll measure little or no B+ until a significant percentage of "full throttle" is reached. I believe it's just a threshhold where, when reached, the 5U4 suddenly fires and a sudden, near-full jolt goes to your vintage caps. This is why most in-circuit "reform" attempts fail.

Build a couple of these (see photo). It is a solid-state 5U4 that uses a pair of 1N5408 diodes as the rectification method. They work at all AC input voltages from 0 to 1000, incrementally and/or smoothly, to avoid this problem.

You'll want to have two of them in your toolbox, one I call left-handed and one I call right-handed. The unbanded side of the diodes go to pins 4 and 6 of the tube base (salvaged from bad metal radio tubes such as 12SA7). The banded side of the diodes, connect together, then connect the joint to pin 2 for a left-handed unit, or pin 8 for a right-handed unit.

It will be up to your specific application as to which unit to use. Either pin 8 or pin 2 will be connected to your B+ supply and power filters. The other will go thru the 5V windings of the power transformer. I don't know that it matters if the high(er) voltage runs thru the 5V windings or not, but I prefer not to do so. So use the unit that corresponds to the pin going to your power filters (i.e. a choke or the 1st electrolytic). 5U4 pins 2 and 8 are symmetrically interchangeable in practice, so don't necessarily trust the Sams schematic. Look at the wiring. I have at least one example where the sams is wrong (my 1949 Magnavox).

This all having been said, I agree that reforming 50-year-old can caps is a risky business. I just use the solid-state 5U4's for slow-starting to avoid smoke-and-flames until I'm sure everything's wired up correctly. After putting in new capacitors.

Somewhere here I read about what the deal is with the 500mfd 15,000 volt cap. It is the HV Filter. I guess I'm wondering if it is more like a ceramic and likely is not bad due to age like the paper caps. Also if it needs replacing I wonder what the trick is to finding a replacemet for that thing. Those are some really large values and I have never seen anything like that for sale at State Electronics (local store).

It looks as if RCA made it easily replacable on purpose. Maybe it was expected to be a weak link that turned out to be really reliable. Who knows? Maybe I'll do a search on the thread concerning this.

Its funny how this whole cap thing works. I tend to be stubborn because I have seen many radios dating back to the thirties that do fine with all or nearly all original caps. Then there is my beloved 56 Philco TV that will and always has come to life like the day it was built. I have a neat Sparton that is the same. There is one difference thought. I bought these sets back in the early 80's as second hand, daily users. Thus they have never been idle for more than 3 or 4 years straight during their life with me. Also I know that at least the Sparton was regularly used by the previous owner. An older gentleman would watch that thing all day on the weekends at an indoor flea market when I was a kid.

I feel blessed in a way to be at least old enough (37) to remember some of these sets still in regular use. The TV repair shops were full of them (junk) and the Goodwill always had a good deal on a nice old black and white, 50's set that someone finally discarded in favor of color. I have had kids come in my house who can not even identify an old set as a television set. They will ask what it is...can you believe it?

Anyway, my point is that the sets that have been idle for say 30 years are going to be very different to revive and can't be compared to something that has been at least in periodic use through the years.

My RCA has several of what look to be factory tubes which tells me that the set may have not been used a WHOLE lot. However, the CRT is a replacement, so it WAS used enough to burn up one CRT. On a guess by just looking at the replaced tubes that the set was not serviced after the sixties. It could have been idle for 40 years.

The HV filter cap is a ceramic type and is not too likely to be bad...it is 500 mmfd (micro-microfarads, or picofarads) not 500 mfd.
Here is a source I have found of these type caps:
http://www.rfparts.com/caps_ceramicdoor.html
If you search for "doorknob capacitors" you will probably find others too.

Regular use does seem to help old electrolytics stay in better shape...I would still replace them myself but if you are going to keep them in it would be a good idea to use an ESR meter and/or capacitance meter after the caps are properly discharged to evaluate the status of the caps, as they do continue to degrade over time.

I highly disagree on both use of solid state rectifiers, and the point of when tube starts conducting. I find that it averages, with a known good rectifier, that it starts producing a low voltage at about 35 volts input on variac.
By 50 volts, you are surging at over 140 volts dc. Mind you, that's surge. As set warms up, this voltage quickly drops. By 85 volats on variac, you are putting out over 200-250 volts dc. At full line voltage, you should get the full dc rated voltage. Note: Back then, the full rated voltage was 117 voolts AC. At least here, in Fl. today's line voltage averages around 124 volts ac.

Further notes, According to John Foltsom to get the correct dc voltages, negative lead of your meter must be connected to chassis.Not to the negative supply lead. RCA was putting in a negative bias supply on this series of chassis. That is why you find the positive terminal of one filter connected to chassis.

Further warning: Remove the black caps going from both sides of line to chassis, as well. You can put in new ones if you wish. I believe the original value on these earlier sets was .01 600volts dc. I personally leave that, and the sometimes installed 270K resistor out of circuit. These two caps were line filters intended to filter out car engine generator noise, medical devices, etc. I find that leaving these two caps out has had NO detrimental affect on the operation of the set. In Fact, with out them, the set is electrically slightly safer on the chassis, making it less of a shock hazzard. Mind you, I'm not saying NO Shock hazzard. I'm saying less.

Please take every precaution on measuring voltages, and handling this set. I'd reccommend one hand behind your back, use clip leads for positive connection, and, have your shoes, and socks on. A rubber matt can also add further protection.

:yes: :yes: :thmbsp: Bill Cahill

The HV filter cap is a ceramic type and is not too likely to be bad...it is 500 mmfd (micro-microfarads, or picofarads) not 500 mfd.
Here is a source I have found of these type caps:
http://www.rfparts.com/caps_ceramicdoor.html


This is what I love about AudioKarma. Lots of real knowledgeable, and kind folks.
I forgot to note the footnote on the Sams capacitor list for my set. The cap is ceramic (which I didnt know) and it plainly says that Electrolytic and Paper Capacitors are rated in mfd. and ceramic and mica are listed in mmfd. Thanks Chad! If I were not straightened out on this I may have spent a lot of time looking for something that would be wrong.

This has been a real informative thread and hopefully will help others in the future. However, sometimes we get into debates on particular things and its hard to really know what is correct. Like the question of weather or not a tube rectifier is producing DC at 50 volts. If not, well my theory is right, and you are not doing anything but the power supply filters any good as far as a "slow warm" goes. The tube is not conducting, so you are not getting DC to any of the paper caps. If the other theory is right then the tube is conducting at reduced voltage we do not need to build a solid state rectifier in order to try slow warming. Hopefully this thread will go on to a conclusion on this matter. All old TV people NEED to know this.

This is not a complaint. I love the debate. It helps to better understand what is going on. Without some debate I doubt the learning process would be as effective as I think it is. Great stuff!! :thmbsp:

Bill -

I'll trust your experience. My Capehart was my first TV restoration (after about 50 radios from circa 1935 to 1950). The mentor who walked me thru the restoration was a lifer TV repairman, and he made me build the Solid-State rectifier for the project. For our capacitor re-form experiment, instead of using a variac, we used a Lionel train transformer, and for the first six or eight hours the line-input voltage was less than ten volts. The first half-hour or so, the measured voltages at the positive-side of the filter caps being under a volt. The output of the 5V transformer secondary at that point would have been something less than half a volt. I don't believe a 5U4 vacuum tube will conduct at all under those circumstances. My understanding is that a very vintage cap, to be reformed, needs to be handled very delicately at first, and the Solid-state rectifier was the proper solution. But I'm new to the game and will happily admit being wrong, if wrong, and hope I didn't misadvise anyone. Thanks for your input.

- Kirk

Tubejunke -

Sorry if we got off on the wrong foot again. I agree we need consensus. Are you saying you think the paper caps need to be brought up slowly too? I've only understood re-forming to apply to electrolytics. Please clarify, and others please add consensus-building comments. Thanks.

- Kirk

When we get an old radio/jukebox/amp etc in for repair we don't even try it till all paper caps and electrolytics are replaced. Having repaired and used tube type equipment for 20 years I can say old caps are just bad news.

Using a silicon diode would work for slowly applying voltage to a cap whereas a 5U4 would not: however I would not trust such a cap to work reliably for an extended period. The old electrolyte just dries out. Paper caps are just bad all the way around! They can not be rejuvenated by any means.

Kirk, I think you get me wrong. No "wrong foot" at all. There really shouldnt be one as long as we are all use tact. I was describing the beauty of the debate with no punn or sarcasm. Again I think it is benificial to those of us climbing the ladder of learning things that they don't teach in school anymore. I am one of those people. Always learning. When that stops I will probably lose interest...I have seen debates where there never is a conclusion, so I was hoping to sort that out. I think we have.

Plus we have learned a neat new experiment that we can try in building solid state rectifiers. Save your old octal tube bases when they go bad. I think you could use them for mounting the diodes and a resistor.

About caps, I thought that the Electrolytics and Paper caps were similar in operation. I also thought that the whole theory of "slow warm" was to slowly charge all of the caps as opposed to throwing a shock to a very dormant system.

I think if we knew for sure that a rectifier tube is in fact conducting at say 70vac on the plates and 2.5 volts on the heater. That is what should be going on with the 100 watt bulb in the line. The power to the transformer is reduced to around half of line voltage. I have not taken a measurement but everything is proportional. (I was told half) If you cut the line voltage in half, everything else will be cut in half, such as the power transformer scondary output to the rectifier.

So, if Bill is right (and my money says he is) then everything is good to go for any of us doing the light bulb slow warm. The 5u4 is conducting at reduced voltage. I guess any of us with a good working set could take some measurements and then we could be more precise. I dont have room to tear apart one of my working sets. I may try to get some measurements from the set this thread is based on. That will only happen when I get more caps......

Any volunteers?

I have had kids come in my house who can not even identify an old set as a television set. They will ask what it is...can you believe it?
:rant:

I definately can get a 5U4 to conduct at only 30 v AC input on variac. Not alot, but, it will conduct.
Now, as for paper vs electrolytics. Paper is NOT the same, and, I agree that it can NOT be reformed, or rejuved in any way.
I further agree that it it far safer to replace the electrolytics.Evn if you do rejuvenate the old ones, it is not likely to last.

I now understand what you were getting at with the solid state rectifiers. However, they aren't less harmfull to the filters. They put more voltage out even quicker than a tube would be able to do, and can cause more harm, alot quicker.

Hope this helps. Thanks. Bill Cahill :yes:

I agree with Chad, replace, do not try to re-form. I tried re-forming on some filter caps used in a couple of AC/DC radios that I have. They re-formed and sounded ok at first. However, after a short time, the radios begain humming as if they had bad filters-they did. I have not had an issue when I re-placed the filter caps.

I also agree that paper caps are bad news all around and should always be replaced.

Took some voltage readings and this is what I found.
The tv chassis is a admiral 24d1 with one 5u4 on top of the power transformer.
With the variac set to 35 vac the power supply voltage was 6.36 vdc
Variac set to 50 vac the power supply voltage was 41.22 vdc.
Variac set to 100 vac the power supply voltage was 289. vdc
All of the electrolytics and paper caps have been replaced in this chassis.
What I have been finding is the sets I did leave the old working electrolytics in, Go bad when I fire up the set after sitting idle. Elcheapo {me} was trying to save money by not replacing the caps the first time around.

I hang a DVM on b+ and bring up the voltage slowly with a variac, using the B+ as a guide rather than the line voltage.

John

Lots of good info. Thanks all.

My Capehart's restoration effort was mentored by the original owner's son, remotely over the internet from about 800 miles away. An interesting mix of frustration and enthusiasm. The set was put away, almost working, in an upstairs New Jersey home's closet in mint condition in 1970. We had a very strong desire to see his dad's set work without any aftermarket tampering whatsoever, which is one pretty good reason to at least try a re-form. In hindsight I could probably have left it alone and have donated it to a nearby Farnsworth museum as-is (which was sort of the original plan). After replacing all the caps, it ceased to be "pristine", and therefore not so much museumworthy. But it works now and I like it.

Our attempt to re-form may or may not have worked. We brought it up slow to 18VAC with the train transformer, then to 95VAC with the train transformer behind a step-up transformer (I bought a variac later, works ok but it buzzes and smokes uncomfortably, in my opinion). At around 95VAC, that's when a few resistors started smoking and cooking nearby components. At this point I lost my nerve and replaced all the wax capacitors. No longer museum perfect, I did the cans too, discarding the possibly reformed cans without ever testing them for good or not. So the re-form ended up an academic exercise only.

Ok, so I just did a simple test with my Sencore tube tester. I put in a good 5U4 testing 100%. I set the filament voltage knob to 1. The meter stayed at zero, no emission whatsoever. I turned the filament knob to 2V, the needle rose to almost the "?" area indicating a weak but good tube. At the 3V setting the tube reads almost normal emission, about 95% of max. The next setting is "4-5V" and at that point the emission is 100%.

1V at the 5U4 filament would already be (roughly) 20% of full throttle, or, say, 25VAC line voltage in our re-form experiment. At this point the HV windings might be putting out 70 or 80 volts but not showing up at the electrolytics at all.

We know by the tube-test experiment that the 5U4 is conducting very well at 40% (roughly) of full-throttle, so the only question is whether or not it's a smooth rise between 20% and 40%, or a relatively sudden ramp-up. Based on some reading on how Thyratrons and other more exotic tubes "fire", I simply surmised that the cathode ions begin to boil at a specific temperature, and are then pretty much boiling. A yes or no condition. This suggests to me a rapid rise between 20% and 40% could occur. At that point there might be 100V coming out of the high(er) Voltage windings. One could imagine a significant amount of that would hit the electrolytics -- a lot more than the fraction of a volt at which you'd want to start reforming a vintage cap. So my theory is that the commencement of ions boiling in a 5U4, on a TV variac warmup, might zap some fragile can electrolytics, that otherwise might have re-formed ok with a solid-state device. That was the theory presented to me by my mentoring authority, so it was the theory I posited here.

I've read in guitar-amp builder's blogs and forums that you don't want solid-state rectifiers in operational gear, unless the amp has a "standby" setting. Something about wanting the other tubes to warm up concurrently, a cold tube with full B+ gets some exotic damage that shortens its life. But that's hearsay info, so take it for what it's worth. I wouldn't run the SS devices in a good TV on a daily basis.

- kb

I think the only problem with the silicon rectifier substitution is that the voltage drop is a lot less (less than 2 volts compared to 30-50 volts or so for the 5U4) so the DC voltage output will be higher than normal. The 5U4 warms up almost instantly so it also provides DC to the amplifier tubes before they are warmed up so on this aspect there should not be much difference.

Nothing but good news on the TC-127!! The whole power supply/transformer issue is no more. What I have now is a raster with what looks like an out of sync picture TRYING to come in. About 2" of vertical sweep is missing. There is no sound. The worst part is the fact that after about 5 minutes the nice, bright raster starts to lose focus and fade out. Thats when I pull the plug.

I still have several paper caps to replace and check resistors and tubes, so theres a lot of possibilities. ALSO, I forgot that I still had two sections of an old electrolytic in use. One is a power supply filter and the other is an output decoupling capacitor.

I say as I get more and more caps replaced these problems will likely iron themselves out. Really the set is on the edge of success as far as I'm concerned. I started with a smoker/flamer!!!

I'm almost there!! Still no sound at all. Thats getting kind of weird. The tuner is a bit goofy also, so in fooling with that I got a signal. With that I see that the horizontal frequency is way off. When I turn the hold control the raster starts to fade. It seems like there is something weird about the brightness and contrast adjustment as well. One of them kind of makes the picture go out of focus and pull in a shadow. The shadow kind of looks as if you are moving the ion trap.

With the improvement of pulling through a video signal I am still happy. Any advice on the missing sound anyone? Tonight I replaced a .01 black paper cap in the sound section. It measured like .165mfd. I hope THIS tranformer (Audio Output isnt burned up too!!

Nothing but good news on the TC-127!! The whole power supply/transformer issue is no more. What I have now is a raster with what looks like an out of sync picture TRYING to come in. About 2" of vertical sweep is missing. There is no sound. The worst part is the fact that after about 5 minutes the nice, bright raster starts to lose focus and fade out. Thats when I pull the plug.

I still have several paper caps to replace and check resistors and tubes, so theres a lot of possibilities. ALSO, I forgot that I still had two sections of an old electrolytic in use. One is a power supply filter and the other is an output decoupling capacitor.


I strongly suggest that you replace all of the remaining paper capacitors before applying power again. By not doing so you are risking damage to more expensive parts. Leaky paper capacitors (and by now most/all of them are leaky) cause excessive current flow which will burn out tubes, transformers, deflection yokes, etc.