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 Post subject: Help, this RCA is driving me crazy.
PostPosted: Apr Thu 23, 2020 1:28 am 
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A different RCA than the last one, this is a 19" portable from 69-70.

Set worked when I got it (years ago), it was unstable and would sync after running a few minutes.
I recapped it (Film caps only, no filters) a couple months ago, now it has an issue with the Vertical.

I would think it's running too fast and stacking the images, but I don't see the blanking bar, and it really just looks like the bottom is stretched so far it's wrapped around and coming down from the top.

The height and Linearity controls seem to work as they should, the Vertical hold can make it roll up or down, but it will collapse to a single line at one end of the control.

I have been over and over the caps I replaced, checking that I didn't install a wrong value, put the lead through the wrong hole, etc.
I even replaced that three legged integrated circuit with discreet components, but it made no difference.

There really aren;t that many film caps in this set, many of the vertical caps are ceramic disc type and they were working previously so it's unlikely they failed suddenly.

The 21LR8 has some wonky voltages on the oscillator side, pin 8 should be 80, I get +33 max, depending on the vert hold setting, . Pin 9 is about -14

B Voltages are pretty close to the 120 & 135 listed. Resistors are pretty close to spec.

Any ideas? I can't help but think it's something I did while recapping, but I've been all over it and found nothing. I'm sure it will be some stupid little thing I overlooked, but I'm going to need some guidance to find it.

Here's the vertical section of the schematic, it's too new (copyright) to post the whole thing without possible complications but this is fair use I think.

Attachment:
schem-rca.jpg
schem-rca.jpg [ 154.25 KiB | Viewed 1925 times ]


And here's a short video of what it's doing.
https://youtu.be/6VJ7MNMlTXo


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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: Apr Thu 23, 2020 1:46 am 
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Hi Eric... Do you have a scope? You might check the B+ for ripple. An open filter cap could drive the vertical circuit nuts.

C47 is a prime suspect, although you said that you changed most of the caps. Another thing to check is the feedback winding on the output transformer.

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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: Apr Thu 23, 2020 2:16 am 
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We used to sell these sets and also did RCA warranty work. Sometimes we had to try 3 or 4 21LR8's to get one to work correctly.


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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: Apr Thu 23, 2020 4:06 am 
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Okay, C47 it is! Yes, I replaced it, I'm also pretty sure I jumped it at some point with another cap, but maybe I just measured voltages, anyhow I jumped it again with a .033 I already had on the counter, it locked right in.

I had a NOS Orange Drop (really Old, 40 years at least) .0027@1600v, the Sams spec is .0027 10% so that should be perfect. I installed it, and it worked, but it was twitchy and hard to adjust the height, so I figure the Orange Drop had gone leaky after all this time.

I pulled it out and installed a brand new .0033 yellow axial, close enough right? Well it behaved exactly like the first one, so I pulled that out and tried a .01, works great, so I tied a .001 and a .0015 together, thats close to .0027, but that didn't work either, so I tried the Orange Drop again, now it doesn't work at all.

I finally gave up and installed a .033 in that spot, now it works great, with one odd exception, the hold control acts like another height control, you can adjust it up or down a couple inches with the hold control, and it still flat lines at one end, I doubt that was the original design?

Maybe Sams has the daa wrong, but most likely I would have just put back whatever was in C47 to start with,I don't think I even had the Sams at that point.

The 21LR8 tests good, but maybe it's a tad gassy? It gets blazing hot pretty quickly, but not red plating, my only other 21LR8 is obviously much weaker when installed, but it behaves the same way otherwise.

Anyway, I'm going to run it like this, the CRT was weak and I rejuvenated it so I probably won't get many hours on it anyway.

This set is nearly identical to one I watched in my early teens, that one was a piece of junk too needing several repairs in it's short life.

Thank you for pointing me in the right direction, I was ready to toss it in the dumpster.

Attachment:
bat.jpg
bat.jpg [ 125.69 KiB | Viewed 1901 times ]


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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: Apr Thu 23, 2020 4:39 am 
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21LR8's, and for that matter most of the other vertical output tubes of that era like 21LU8 and 17JZ8 can check perfectly well on a tube tester but behave quite unpredictably in the set. I can verify the earlier observation that many times we had to try several to find one that would work properly in any given set.

Of course back then when the sets were fairly new, it was unusual to find film type caps bad, but occasionally one would have a bad section in an electrolytic can.

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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: Apr Fri 24, 2020 12:13 am 
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It's not uncommon for vintage Orange Drops (with the Difilm paper/Mylar construction) to develop a kind of ESR. I check every one on the TO-6, and if the null indication is "squinty", out it goes.

That feedback circuit from the vertical output plate is a big trouble spot. Zenith sets had trouble with that three lead coupling network.

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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: Apr Fri 24, 2020 1:02 am 
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Tim Tress wrote:
It's not uncommon for vintage Orange Drops (with the Difilm paper/Mylar construction) to develop a kind of ESR. I check every one on the TO-6, and if the null indication is "squinty", out it goes.

That is the paper part becoming leaky. So you effectively have two caps in series, a Mylar cap and a paper cap. The paper cap has a resistor across it.
I used mine up as audio coupling caps and bypass caps. Any application where the cap just has to be big enough rather than any certain value.

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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: Apr Fri 24, 2020 10:10 pm 
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Location: New Hampshire
When working a vert problem keep in mind voltages in both the osc & output
will ALL be off & rarely give you a clue. Most common things are
1) high ohm resistors around the height control. Lift to test !
2) caps in feedback loop from the output plate to osc grid ( your problem).
3) electrolytic cap at output cathode when used. ( lin problems ) .
Thats after trying a tube first !

Nice repair !

73 Zeno 8)
LFOD !


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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: Apr Sat 25, 2020 12:49 am 
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Tom Schulz wrote:
Tim Tress wrote:
It's not uncommon for vintage Orange Drops (with the Difilm paper/Mylar construction) to develop a kind of ESR. I check every one on the TO-6, and if the null indication is "squinty", out it goes.

That is the paper part becoming leaky. So you effectively have two caps in series, a Mylar cap and a paper cap. The paper cap has a resistor across it.
I used mine up as audio coupling caps and bypass caps. Any application where the cap just has to be big enough rather than any certain value.


I've also had a lot of trouble with vintage orange drops. They tend to measure 50%-100% above rated value, and also have 10-100 times the normal dissipation factor that a film cap should have. Interestingly, I haven't seen this with other dipped caps from that era (brown drops, maroon drops,...). They don't measure leaky, but I wouldn't trust them since the mylar layer is seeing all of the voltage now.


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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: Apr Sat 25, 2020 2:22 am 
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That's sad news about the Orange Drops, I bought a whole batch of them cheap on eBay a while back because there were a lot of 1600 volt ones in hard to find values. I've used a few in other sets with no apparent issues, possibly in less critical circuits?

I've been using the set to watch some of the same stuff I would have watched on my original set back in the early 70's, it's worked without a glitch so far, One of the few old sets I have that doesn't have some intolerable defect, like Buzz in the sound on bright scenes or retrace lines from Macrovision, the linearity isn't perfect but it's close enough to hardly notice.

If this set had a strong CRT I'd be willing to spend whatever time it took to get it 100%, the ETF had one at one point, but my luck shipping CRT's was about 50% so I let it pass.

I won this set in an eBay auction a long time ago for something like $0.99 or $1.99 (I gave him $20 extra to make it worth his time to pack) the seller had several of them so possibly a Motel set.


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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: Apr Sat 25, 2020 2:31 am 
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Eric H wrote:
That's sad news about the Orange Drops, I bought a whole batch of them cheap on eBay a while back because there were a lot of 1600 volt ones in hard to find values. I've used a few in other sets with no apparent issues, possibly in less critical circuits?

I was only the first type that they made that used the paper/Mylar insulation. They were called DIFILM Mylar-paper. The part number started with 6PS. After awhile the got smart and switched to just using Mylar. I never could understand why they used paper in the first ones.

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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: Apr Sun 26, 2020 2:55 am 
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Put in a NOS RCA 21LR8 and the linearity improved 100% The Hold control doesn't have much effect on the height now either.


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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: Apr Mon 27, 2020 11:10 pm 
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That's good to hear it works so much differently with a new 21LR8, shows how unpredictable those tubes can be.

IIRC some/many of the originals used in production were sourced from Japan, the later replacements that worked the best quite often were Sylvania manufacture no matter what brand name was on them.

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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: Apr Mon 27, 2020 11:29 pm 
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Mr. Detrola wrote:
21LR8's, and for that matter most of the other vertical output tubes of that era like 21LU8 and 17JZ8 can check perfectly well on a tube tester but behave quite unpredictably in the set. I can verify the earlier observation that many times we had to try several to find one that would work properly in any given set.

Of course back then when the sets were fairly new, it was unusual to find film type caps bad, but occasionally one would have a bad section in an electrolytic can.

Another common tubes that were very unstable was the 15KY8 tube. That tube is Finicky.
I think it's interesting that the 21LU8 tubes were unstable, considering it is a color television tube. The 21LR8 types were also color TV tubes. Interesting.

It also goes to show that the tube testers can lie.

Orange drops were considered very good. Sad.

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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: Apr Tue 28, 2020 3:43 am 
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I don't know if the .0027 Orange Drop was actually bad now. The set wouldn't work with less than a .01 cap in that spot, but maybe it was because the tube was no good. I'm not going to take it apart again to find out. :lol:


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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: May Fri 01, 2020 12:11 pm 
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Regarding Orange Drops, and not to hijack this thread, but I've never had a problem with one in actual use. Yes, they sometimes do show a wonky eye tube indication on the Sprague TO6, but then end up working just fine. Not having done extensive research into this, I just chalked it up to "they are about as good as they were made to be" ... and in actual use, that seems to be the case.

YMMV

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 Post subject: Re: Help, this RCA is driving me crazy.
PostPosted: May Fri 01, 2020 6:46 pm 
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Barry H Bennett wrote:
Regarding Orange Drops, and not to hijack this thread, but I've never had a problem with one in actual use. Yes, they sometimes do show a wonky eye tube indication on the Sprague TO6, but then end up working just fine. Not having done extensive research into this, I just chalked it up to "they are about as good as they were made to be" ... and in actual use, that seems to be the case.

YMMV

Depends on the device. Radio and audio application they usually work fine, monochrome TV they usually work okay but sometimes have enough time effect to bother me, 60s color sets like the CTC11-15 they can make night and day changes in video and sweep performance....heck on a CTC15 chassis I have one of the orange drops next to the a tube on the PCB had split open and tested leaky on top of the fuzzy eye on the capacitance reading.
If a drop tests like new on my Heathkit C3 I'll leave it but off it don't and the stage it's in ain't performing well out it goes.


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