Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Dec Thu 05, 2019 3:18 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 18 posts ] 
Author Message
 Post subject: RCA 21T176 First Impressions
PostPosted: Oct Mon 14, 2019 5:16 pm 
Member

Joined: Feb Wed 03, 2016 9:11 pm
Posts: 63
Location: Savannah, GA
Hello all, with my first television restoration now completed I am eager to get started on another. I picked up this RCA/Victor 21T176 console from an individual in Jacksonville Florida. It appears to be a well kept set as it has been in the same family since its original purchase, and kept in storage for the past couple of decades. I did find a couple of things that raised concern. First, it appears that the horizontal output transformer has become unwound, and whatever green stuff holding it together melted at some point. Secondly, there is this piece of copper running from HV cage to the CRT where it secured by tape. Clearly the horizontal trans is going to need rewinding. How difficult is this to accomplish? I have dealt with unwound transformers once before in a Philco radio, but it has been sometime. Is this copper piece normal? Thank you.

Horizontal output transformer
Attachment:
20191014_113154.jpg
20191014_113154.jpg [ 419.75 KiB | Viewed 959 times ]


Piece of copper which ran up to the CRT
Attachment:
20191014_113224.jpg
20191014_113224.jpg [ 696.93 KiB | Viewed 959 times ]


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Oct Mon 14, 2019 6:20 pm 
Member
User avatar

Joined: Nov Thu 11, 2010 6:03 pm
Posts: 961
Location: Pewaukee, WI
I suspect that the piece of copper didn't come from inside the the HV cage...

The winding is indeed crooked, but may still work (check continuity). If it hasn't gone open heat it with a hair drier or heat gun until warm enough that all the wax softens then gently straighten while warm and let cool (double check continuity). It was not uncommon for flybacks to run hot enough (especially before air-conditioning was universal) for the wax to melt off.

Try to save the original before looking for a new one or rewinding...most rewinding operations can't handle flyback transformers from TVs.

Earlier this year I was running a working 60s Philco and wanted to know if the flyback was getting warm. As soon as I turned it off I grabbed the flyback winding that was quite warm and in my enthusiasm I slid the winding about 1/4" off kilter...I immediately straightened it, let it sit for a bit and powered it back up and it was just as happy as it was before I moved the winding...when I get more time I plan to reduce horizontal current to cool that fly.


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Oct Mon 14, 2019 6:30 pm 
Member
User avatar

Joined: Aug Tue 28, 2018 9:22 pm
Posts: 1310
Location: Sanford Fla 32771
Copper strap may be from the CRT glass to chassis ground. Some CRT had a conductive coating on the outside and needed to be grounded.

_________________
Paul of Florida (Click below for my collection)
https://paulsironhorse.smugmug.com/


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Oct Mon 14, 2019 8:15 pm 
Member

Joined: Feb Wed 03, 2016 9:11 pm
Posts: 63
Location: Savannah, GA
pauls.ironhorse wrote:
Copper strap may be from the CRT glass to chassis ground. Some CRT had a conductive coating on the outside and needed to be grounded.


That looks to be what it is used for. It was taped onto the coating of the CRT. Now for the transformer, what is this best way to go about checking continuity in these types of transformers? I tried checking from the plate of the H.V. rectifier to the plate of the Horizontal output tube. This to me would seem to check continuity from one side of the transformer to the other, but I did not get a reading. I have found the schematic online here https://www.yumpu.com/en/document/view/28018094/1952-rca-21t176-early-television-foundation the transformer in question is "T3". Thanks for the help


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Oct Mon 14, 2019 8:20 pm 
Member

Joined: Sep Fri 07, 2007 2:27 am
Posts: 6219
Location: Grand Chute, Wisconsin
Chase.Parten wrote:
I have found the schematic online here https://www.yumpu.com/en/document/view/28018094/1952-rca-21t176-early-television-foundation the transformer in question is "T3". Thanks for the help
You can also find the RCA factory manual for this set at the ETF site: http://www.earlytelevision.org/pdf/rca_ ... a-1951.pdf

.


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Oct Mon 14, 2019 8:57 pm 
Member
User avatar

Joined: Nov Thu 11, 2010 6:03 pm
Posts: 961
Location: Pewaukee, WI
Looks like you need to measure from pins 1 to 3 and look for approximately 300 ohms...if open you may need a new flyback.


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Oct Mon 14, 2019 9:27 pm 
Member

Joined: Feb Wed 03, 2016 9:11 pm
Posts: 63
Location: Savannah, GA
I tested pins 1 to 3 and it checked out okay. Now I just need to get that birds nest of a winding straightened out. How precise would you say I need to be with this repair? How much can the winding being scattered as it is effect performance? Thank you.


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Oct Mon 14, 2019 10:37 pm 
Member
User avatar

Joined: Nov Thu 11, 2010 6:03 pm
Posts: 961
Location: Pewaukee, WI
Chase.Parten wrote:
I tested pins 1 to 3 and it checked out okay. Now I just need to get that birds nest of a winding straightened out. How precise would you say I need to be with this repair? How much can the winding being scattered as it is effect performance? Thank you.


It is hard to tell how scattered it is from the picture (not sure if I'm seeing cobwebs or coil wire). You want to tuck it back into the winding as best as you can while not damaging the insulation/wire and also avoiding mixing layers of the coil...if all that stuff is spit out winding it may be difficult to sufficiently repair. There's usually somewhat decent tolerance for unevenness or deleted turns in most designs. Letting it hangout is inviting destructive arcing.

May want to look up the RCA flyback part number and the compatible subs in the Sam's and put out a want ad for them.


Last edited by Electronic Memory on Oct Mon 14, 2019 10:45 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Oct Mon 14, 2019 10:39 pm 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 1832
Location: Dallas, TX
If that set has the original CRT type (21AP4) then it is a metal shell bell which is also the second anode (HV) connection. So that strap would not be a ground strap to the CRT bell area. It might go to the yoke area.
You should read the CRT data if it is a 21AP4.
https://tubedata.tubes.se/sheets/079/2/21AP4.pdf
The metal shell was a way of reducing the weight but it meant a large piece of metal at high voltage. Insulation is very important here.
That flyback may need replacing if the wire has come loose.

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Oct Tue 15, 2019 1:50 am 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 28013
Location: Detroit, MI USA
I wouldn't even fool around with the flyback. Just buy a replacement. That was a really common one, but also a high failure item. I don't think the one with green insulation is original to the set anyway it looks like a later aftermarket replacement.

_________________
Dennis

Experience is what you gain when the results aren't what you were expecting.


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Oct Tue 15, 2019 3:11 am 
Member

Joined: Feb Wed 03, 2016 9:11 pm
Posts: 63
Location: Savannah, GA
Replacement seems like the best option. I have already contacted Moyer Electronics about the flyback. Out of curiosity what are some other sources for obtaining these type of parts?


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Oct Wed 16, 2019 5:09 am 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 28013
Location: Detroit, MI USA
From time to time you will find them listed on eBay usually by sellers cleaning out the estate of old time TV repairmen, and those sellers don't have much of an idea what they are offering, so you need to know part numbers not only for your original, but also for any aftermarket replacements that may have been available back in the day.

_________________
Dennis

Experience is what you gain when the results aren't what you were expecting.


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Oct Sat 19, 2019 1:40 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 10555
Location: Redlands CA
The schematic lists a Merit HVO-8 as a replacement, there's one on eBay now, though it looks quite different, possibly a revised design? It looks like it may just be the high voltage donut?

The green wax on the one you have makes me think it was a Merit also, they used that green on most of their Flybacks.

https://www.ebay.com/itm/NOS-Vintage-Me ... SwwfFb-0hR


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Oct Sun 20, 2019 4:24 am 
Member

Joined: Feb Wed 03, 2016 9:11 pm
Posts: 63
Location: Savannah, GA
I believe I may have found it here. This looks very similar anyhow. https://www.ebay.com/itm/NOS-Vintage-Merit-Coil-Transformer-Co-Fine-Radio-Parts-HVO-33-RCA76501/233145135646?hash=item364888721e:g:AgoAAOSwtmNb-0tv The Merit Part No. is different, but the RCA matches up. Was that kind of thing common? Thanks.


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Nov Fri 08, 2019 8:31 pm 
Member

Joined: Feb Wed 03, 2016 9:11 pm
Posts: 63
Location: Savannah, GA
Alright, at this point the new flyback transformer is installed and the set has been recapped. I powered the set on, but got nothing. l then checked all the plate voltages which were good, but as I was checking the high voltage (which was very low) I manipulated the brightness control causing a filter capacitor to pop, lights to dim, and smoke to emerge from the set. I had checked the B+ circuits for shorts previously, and the power transformer, rectifier tubes, and the filter choke. Now it seems the entire B+ circuit is shorted to ground. I can not figure out why a small adjustment of the brightness control would cause such a major short within the set. Where is a good place to start in finding the cause of this short?


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Nov Fri 08, 2019 8:51 pm 
Member
User avatar

Joined: Nov Thu 11, 2010 6:03 pm
Posts: 961
Location: Pewaukee, WI
Could be your control has tin whiskers in it and when you turned it one of those whiskers shorted the B+ end of the pot to the grounded case of the pot...to check that unsolder the B+ terminal of the pot and measure it's resistance to ground, if it is low and or does not vary correct with pot adjustment then you got a whisker...to fix uninstall the pot and open up the pot, clean the inside thoroughly with contact cleaner and paper towels (use 400.grit or finer on the metal to knock the whiskers off) reassemble and test the pot before reinstalling it in set.... follow up by checking any series resistors between the pot and the power rectifier.

If the pop really was a cap then check all the caps especially the one that popped (if you know which it was).


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Nov Mon 11, 2019 7:03 pm 
Member

Joined: Feb Wed 03, 2016 9:11 pm
Posts: 63
Location: Savannah, GA
The pot seemed to have checked out fine. I ended up going along the B+ circuit disconnecting each component until I found the one that had shorted. It ended up being one of the filter caps, a different cap from the one that popped. I suppose at this point I am going to replaced the 2 faulty capacitors, verify there are no more shorts in the circuit, and power the set back on. Still seems a bit strange. How common is it for a brand new cap to short during the first power on? Could I be looking at a larger issue than the capacitor? Thanks


Top
 Profile  
 
 Post subject: Re: RCA 21T176 First Impressions
PostPosted: Nov Mon 11, 2019 7:13 pm 
Member
User avatar

Joined: Mar Sun 01, 2009 10:27 pm
Posts: 5045
Location: Ann Arbor, MI
New parts can be bad, but 2 new caps being bad is quite unusual. Now if the caps were new old stock than the failure would not be unusual.
Make sure that the caps were not installed backwards and that the voltage rating is at least as high as the original caps. Traditionally electrolytic caps had the negative lead marked. But recently some cap manufactures have taken to marking the positive lead. Look carefully at the caps and look for a minus sign or a plus sign. Don't just assume that the marked end is negative.

_________________
Tom


Top
 Profile  
 
Post New Topic Post Reply  [ 18 posts ]  Moderators: 7jp4-guy, Mr. Detrola

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 3 guests



Search for:
Jump to:  




























Privacy Policy :: Powered by phpBB