PLEASE help! Early RCA experts check this out.. - Videokarma.org TV - Video

Tubejunke · #1 07-19-2006, 01:58 AM

I'm the person who got the TC-127 on another thread. Well, the thread died and I have some pitfall updates, so here goes. As I said before I tried to slow warm the set at 60v.a.c. for about 4 hours. At the time I had tube filaments lighting and a fairly dim 100watt light bulb. Things were looking good.

When I applied 110v.a.c. the transformer gave a good buzz and the circuit protector kicked out on my voltage spltitter. There was a smell of burning old tv with no smoke and a hot line cord. Heres the part I hate. I hooked up my low voltage lamp rig again and now I have a fully bright light with no tube fillament action now.

Now I have a huge current draw and little or no power to the heater string. Now before everyone determines that I did the damage I must add that the 5u4 Rectifier was shorted when I first hooked her up. Same effect, bright light. When I replaced that I got the heater string to burn at 60v. I think I am taking up where someone elses problems left off.

So now if my theory is correct and I have a bad transformer I guess I am screwed. The heavy draw with new caps and still little or no voltage to the heater string, and fully bright bulb tell the tale. I figure a repacement will be a needle in a haystack.

Sorry for being so long. Now I am hoping we have an early RCA guru here on Audiokarma with some great news....I really like this set and now I fear it is another hopeless case. Its in super shape so I hate thinking it is fried in a really bad way....

Thanks for reading this and any advice.....

***Eric H*** · #2 07-19-2006, 02:07 AM

If you remove the 5U4 do you still have the heavy draw?
The fact that the original 5U4 was shorted probably means you have a shorted filter cap or something else on the B+ line.

It's possible it took out your transformer too but it shouldn't be too hard to find a replacement for that.

Tubejunke · #3 07-19-2006, 11:01 PM

Hi Eric, thanks for the reply! Not much life around here lately. Yes I have the heavy draw with or without the 5u4. I may have mislead about replacing the caps. I replaced all of the caps in the power supply that had the lowest resistance. All should fall into the mega-ohms right? I also use an anolog meter and nothing looked strange. All have a good "kick". C2 did not get touched as it had the best readings of all. C2 is the only multi section electrolytic with all three sections being power supply filters. HMMM??? On the others I just replaced the filter section. I have often wondered if multi section caps can have shorts between the sections. Something to think about..

Maybe there is still hope for my transformer. I have heard of old caps only acting up when a load is put on them. One would still think that a component messed up enough to cause this heavy draw would be noticable with a meter.

My old 8t-243 that I mention used to blow the 5u4 within seconds and these same procedures gave me good results. I always have THAT transformer (if compatible) but I have heard that the 8t-243 is more rare than my TC-127. I would not want to ruin that although I think it is ugly and had wished someone would take it off my hands. I always wanted a double d style round tube set that doesent weigh a ton like my old Dumont RA-109A. I GAVE that set away just to get it a good home. Simply too big and heavy.

Thanks for reading and any info or suggestions.

Phil Nelson · #4 07-20-2006, 12:11 AM

Quote:

Originally Posted by Tubejunke

I also use an anolog meter and nothing looked strange. All have a good "kick". C2 did not get touched as it had the best readings of all. C2 did not get touched as it had the best readings of all. C2 is the only multi section electrolytic with all three sections being power supply filters.

Sorry if I'm off base, but . . . do you mean that you checked the power supply electrolytics by testing their resistance with an ohmmeter? I have found that to be an unreliable test. I believe the best test is done with a cap checker that applies the actual working voltage.

I speak as one who has fried a couple of power xfmrs in the past, by running a 'working' set before replacing all of the power supply electrolytics. Now, I don't even think about it. Those filters are the first things to go!

Regards,

Phil Nelson
http://antiqueradio.org/index.html

Tony V · #5 07-20-2006, 01:28 AM

Probably your best bet is to go ahead and replace ALL of the electrolytics as they can short between the sections. Another thing as everyone can tell you is that in a set that old even if the caps check good when tested doesnt mean that they would hold up for very long even if the set would have worked when you applied full voltage. So as a reliability issue its best to replace them especially since their not all that expensive. Dont assume the tranny is bad yet until you do this. As Phil said these particular trannys are fairly common so dont give up the ghost yet. I have a couple roundie sets you might be interested in if it comes to that point and we're within driving distance as i dont like to ship tv sets. Good luck!
Tony

roundscreen · #6 07-20-2006, 07:57 PM

No expert here but Here is a way to test your transformer. Remove the 5u4. Mark all the wires going into the transformer and disconnect them. Run the ac line from your voltage splitter and light bulb to the primary winding wires and turn on. See if you get a short still. If no short, Hook up the secondary winding wires one at a time. { I do the heaters first} That may lead you to the problem. Also, Look for wax caps on b+ lines.
It does sound like the transformer is bad from what you have been writing. That weird smell and the hot cord. B Careful, A bad transformer can make the chassis go to the hot side of the ac line. The other guys are right, Get rid of all the old electrolytic caps.
ED

Tubejunke · #7 07-21-2006, 12:29 AM

Thanks everyone for the usefull info. I really like the idea of that capacitor tester that applies a load on the cap. Probably costly though. Really I go with the general idea that replacement of all caps in the power supply is the way to go. Now I only can pray that the C2 3 section that I left alone is completely shorted.

I have only applied 110 for less than five seconds the 2 or three times I have tried this set. I'm hoping the smell is the C2 heating up, and I know they can heat up quick. The transformer has not even got warm but one time. The first time....If I get out of this one I'm going to put fuses in this set on every lead from that transformer.

Wish me luck........

kbmuri · #8 07-21-2006, 03:29 PM

Tubejunke -

Not necessarily expensive. Look for one of these at your next hamfest, junk shop, or eBay. I think I paid ten bucks for this one. Found a pdf of the manual online for free.

eBay example: http://cgi.ebay.com/ws/eBayISAPI.dll...m=290009347083

Thom · #9 07-21-2006, 04:00 PM

I got mine on Ebay for $15.00. Well worth the price considering what it will tell you about the capacitor before applying power. You also might want to consider a variac. Fuse the output and you are good to go. I know replacing caps can be a pain in the neck and not necessarily cheap for the big ones but at least they can be found or compiled far more easily than a multi-tap transformer. My advice: replace the caps. Old ones cannot be trusted and when they give up the ghost, like an airline pilot, they usually take others with them. Good luck.

Tony V · #10 07-21-2006, 08:02 PM

You hit it right on the nail head Thom

Tubejunke · #11 07-22-2006, 01:38 AM

Oh, I didnt know that the cap checker was a vintage piece of equipment. Thats cool but on the other hand some vintage equipment requires the same cap repair that the set needs. I have a great old early 50s tube tester that wont test CRT's any more. I really liked that when it worked. No repair attempt has been made other than pulling the main board from its case. What did I find? A TUBE!!! Thats right the tube tester in some way depends on the very thing it is testing. I hate to admit it but I prefer solid state test equipment. I dont want to test my testers in other words. With everything else tubes RULE!

I'll post again when I get that C2 replaced in the TC127. It may be a while because I missed the electronics shop Friday and I'm changing to a M-F 8-5 job next week. I'm used to having a M-F day off and had forgot how hard it is to get anything done because of being stuck at work when everything else is open for business. Oh well maybe I'll start ordering them online. If gas gets higher I will have to......

kbmuri · #12 07-22-2006, 06:07 PM

Yeah, I recapped and re-tubed the Heathkit Cap Checker (pictured above), so I guess my ten-dollar price jumps to 30 or 35. After that, it calibrated easily and is a valuable work horse.

My Sencore tube testers each have one 12AZ7 tube under the covers. Both are 40+ years old and both still have the original tube and each checks the other tube as NOS. So whatever the tube tester uses it for, it's apparently not a heavy load. And I suppose the tester isn't on continuously like a TV or radio, so the hours on each 12AZ7 is probably still pretty low. If the 12AZ7 went bad in either, I'd just pop another one in and go. What will you do when your solid-state IC craps out?

I agree a person should put in all new caps, but for one, you're not guaranteed the new cap you just bought hasn't been sitting on a shelf in the sun for two years, or wasn't a "return" part, or wasn't just a factory defective. Small insurance to test each cap before putting it in.

If you're troubleshooting, it sometimes pays to leave in caps that test good, and focus on the ones that test bad, until you've got a working set (TV, Radio or Audio), and then decide if you want to recap the entire thing.

The main power-filter caps are, indeed like a airline pilot, they take others down with them. But the smaller paper caps, even the micas and ceramics, can also go bad (although rarely). The Heathkit above tests them all. Definitely worth the price of admission.

*Bill Cahill* · #13 07-22-2006, 09:36 PM

Hold it!! You guys missed one possibility. There are two black beuty capacitors on both sides of line cord going to chassis. Cut themn out. Then, do the light bulb test again without the 5U4.

I also agree that a resistance test is a very un reliable test for caps. Further, I agree that you would be far better off replacing ALL Electrolytics.

Good luck.

Bill Cahill

Whirled One · #14 07-22-2006, 10:36 PM

Those old capacitor testers are great. You might be surprised how many caps test okay at the low voltages supplied by a modern meter or tester, but fail miserably when you run the leakage test on one of those old capacitor testers at successively higher working voltages. As others here have said, these things are common at hamfests for about ten bucks, and well worth it-- even though, yes, you may end up having to re-cap the cap tester first.