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 Post subject: Predicta 10L43 [Update: 6/10/19]
PostPosted: Apr Tue 09, 2019 3:41 am 
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Location: Kansas City, Missouri
Hey All,

Tonight I powered up my 10L43 for the first time. I wouldn't be this far without all the help you folks have given me and for that I'm grateful.

I was preparing myself for the worst, and was pleasantly surprised The whole thing powered up and the CRT lit up. I've not yet run a signal through the set, focusing on getting a good raster.

What I've got right now is a really squashed raster. It's more than a horizontal line, it's about a half inch thick and definitely has some life. I just can't get a full picture. Also, I'm not getting any sound from the speaker as far as static or noise. Below is a picture, and don't worry, I've got the contrast and brightness cranked down to protect the CRT.

I've started to check voltages, but it's kind of hard to know where to source things. But on my initial check, things are definitely out of whack, some voltages high, others low. Also, I've tested all the tubes, so they all should be solid. It looks to be something elsewhere. Based on the symptom you see, where would you suggest I start?

Image


Last edited by Brianruns10 on Jun Mon 10, 2019 3:33 pm, edited 2 times in total.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 09, 2019 4:32 am 
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Joined: Aug Sat 16, 2008 10:42 pm
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The coupling capacitors in the vertical circuit, if original, can be replaced and you should see some improvement. Also, I had one of these where the height control had completely failed inside and nothing was getting through it. Last line of offense are those couplate modules. I had to reconstruct both of them in a recent repair job and that made everything OK. Of course the tube socket interface to the PC board and the pin grip to the tube itself can fail causing this. Did you wiggle the vertical output tube CAREFULLY and SLIGHTLY to see if anything changes?

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 09, 2019 3:55 pm 
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Joined: Dec Tue 10, 2013 4:36 pm
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Location: Kansas City, Missouri
So here's a new development: I powered it up this morning to fiddle some more with the set, and the raster was bigger, about an inch in height, despite my having done nothing to change the settings.
I've also noticed my flyback is making a bit of humming/crackling noise. The original coating was pretty chipped so I had to apply several coatings of new, neutral acting silicon to seal it. Could the two things be related?


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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 09, 2019 5:59 pm 
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Joined: Aug Sat 16, 2008 10:42 pm
Posts: 175
The flyback behavior and poor V sweep are not related in my view. The width control has big effect on the HV level. Use a HV probe to confirm the width setting is not causing too much HV. If HV is in correct range, the flyback should not be making noises. Are you sure you got all the bugs out?
As for sweep height getting better, I would still suspect poor contact on V output tube pins n socket. Are you the guy who rebuilt the V LIN control? It seemed from that discussion that you would never get below 180 ohms on cathode of that tube which could limit height. I try to never run any TV at max anything including V sweep. If you have to run the pot wide open, something else is wrong like coupling capacitor or couplate boards. But imposing a 180 ohm ceiling (or floor?) on there will limit the range of the control in imperfect way.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 09, 2019 6:28 pm 
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Yep that was me, I rebuilt the V-Lin. The issue there is that the original had a range of 180 to 1320 ohms. The nearest I could get was a 0 to 1500 ohm resistor, and not wanting to expose the cathode to the full current, I put on a 180 ohm resistor in series to serve as a limiter. I'll check my work to see if I made a mistake there, and I'll dig further into those areas you mentioned. It may also be I made a mistake in one of the networks, since I rebuilt all of them.

BR


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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 09, 2019 6:56 pm 
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I always apply Occam's razor: chase the simplest explanation first. That would be tube pin socket connections. I still believe the original pot from philco had a detent in it; not a hard limit at 180 ohms. They don't WANT that cathode at zero ohms but it might like 100 or even 50 to get full sweep and so be it is my view.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 09, 2019 7:28 pm 
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That makes a lot of sense, and I'll check out everything you suggested. I have some lower ohm resistors I'll try out to see what happens there, and check out the pins as well. Thanks for all the great advice!

BR


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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 09, 2019 7:32 pm 
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thomash85715 wrote:
I always apply Occam's razor: chase the simplest explanation first. That would be tube pin socket connections.
I still believe the original pot from philco had a detent in it; not a hard limit at 180 ohms. They don't WANT that cathode at zero ohms but it might
like 100 or even 50 to get full sweep and so be it is my view.

I don't think it would have been a detent. That would be too easy to go past. And that last photo shows the height a long way from full height.
A few ohms lower would not make anyway near enough difference in height.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 09, 2019 9:55 pm 
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Joined: Aug Sat 16, 2008 10:42 pm
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I have worked on four predictas and they all like that pot at about 90% to get full sweep. But in fact I have never measured the resulting ohms at the correct setting so I might be wrong on my detent theory. Still, why would philco order a pot with a hard stop on it at 180? Would it not be cheaper to park a resistor downstream and use off the shelf pot? Is this sort of what you did Brianruns? sorry if I got your name wrong; I can't see it from this panel.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 09, 2019 11:11 pm 
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thomash85715 wrote:
I have worked on four predictas and they all like that pot at about 90% to get full sweep. But in fact I have never measured the resulting ohms at the correct setting so I might be wrong on my detent theory. Still, why would philco order a pot with a hard stop on it at 180? Would it not be cheaper to park a resistor downstream and use off the shelf pot? Is this sort of what you did Brianruns? sorry if I got your name wrong; I can't see it from this panel.



Actually the question of the pot was a real stumper for me and for others I asked. The schematic is a little vague on this point, and varies depending on if you use the Sam's or the Philco. Here is the Philco:
Image

And here is my replacement build:
Image


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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Wed 10, 2019 12:23 am 
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Location: Grand Chute, Wisconsin
Brianruns10 wrote:
I've also noticed my flyback is making a bit of humming/crackling noise. The original coating was pretty chipped so I had to apply several coatings of new, neutral acting silicon to seal it. Could the two things be related?
I've always been reluctant to seal flybacks, afraid to seal moisture in them. Not sure if this may be part of your problem, just throwing the idea out there.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Wed 10, 2019 1:40 am 
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Brianruns10 wrote:
And here is my replacement build:

I see the problem! :!: The wiper is not touching the element! :)

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Wed 10, 2019 1:42 am 
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Multiple layers of silicon might fall under the category: too much of a good thing. If you can get some off without destroying underlying materials, I submit that would be a better situation. That flyback does need to breathe a little bit I would suggest.
As for V LIN, did you put in a new 100uF capacitor already? It appears that even wide open, your pot will not achieve maximum power on that tube which I guess is the idea.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Wed 10, 2019 2:03 am 
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Joined: May Thu 14, 2015 4:15 pm
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Brianruns10 wrote:


Actually the question of the pot was a real stumper for me and for others I asked. The schematic is a little vague on this point, and varies depending on if you use the Sam's or the Philco. Here is the Philco:

That arrangement doesn't make much sense to me. It would simply limit the resistance range from zero to 1320 ohms.
You could set it to 180 ohms. A precision 1320 ohm pot (or a 1500 with a stop) would cost more than a 1500 ohm 20%
so why would they choose that. More likely the schematic is wrong, maybe the range should be 1320 to 1500.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Wed 10, 2019 4:52 am 
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Notimetolooz wrote:
That arrangement doesn't make much sense to me. It would simply limit the resistance range from zero to 1320 ohms.
You could set it to 180 ohms. A precision 1320 ohm pot (or a 1500 with a stop) would cost more than a 1500 ohm 20%
so why would they choose that. More likely the schematic is wrong, maybe the range should be 1320 to 1500.

Here is the link to the thread about the pot.
https://www.antiqueradios.com/forums/viewtopic.php?f=3&t=356929
The conclusion for most people was that the person drawing the schematic flipped the schematic of the pot end for end.
I think that the manufacturer of the pot did not charge very much for moving the stop on an otherwise standard 1500 ohm pot.
Especially if they bought a large quantity.
And that saved the cost of a resistor and the cost of installing the resistor.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Wed 10, 2019 3:00 pm 
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I agree that Brianruns10 probably has it right. Still it seems a coincidence that he is having vertical problems.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Wed 10, 2019 11:26 pm 
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Tom Schulz wrote:
Notimetolooz wrote:
That arrangement doesn't make much sense to me. It would simply limit the resistance range from zero to 1320 ohms.
You could set it to 180 ohms. A precision 1320 ohm pot (or a 1500 with a stop) would cost more than a 1500 ohm 20%
so why would they choose that. More likely the schematic is wrong, maybe the range should be 1320 to 1500.

Here is the link to the thread about the pot.
https://www.antiqueradios.com/forums/viewtopic.php?f=3&t=356929
The conclusion for most people was that the person drawing the schematic flipped the schematic of the pot end for end.

I think that the manufacturer of the pot did not charge very much for moving the stop on an otherwise standard 1500 ohm pot.
Especially if they bought a large quantity.
And that saved the cost of a resistor and the cost of installing the resistor.

Bingo, the only modification to std pot is relocating stop indent in back cover. That would stop wiper at 180 ohm vs zero.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 16, 2019 4:14 am 
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Joined: Dec Tue 10, 2013 4:36 pm
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Location: Kansas City, Missouri
Hi All,

I've been out of town and away from the work bench until yesterday, so I've been unable to work on my issues with the 10L43. So I have an update, with some new puzzles.

I focused in on the vertical output osc. tube (6DR7). With the set powered up, I tested the voltages of every pin. Pins 1-5, and 9 were almost exactly as they should be, well within tolerance.

However, pins 6, 7, 8, associated with the vertical oscilator half of the tube all had values that were drastically wrong when measured with my multimeter They were as follows:

Pin 6: Expected: 130v; Actual: .8v
Pin 7: Exp: -3.2v; Actual: -300v
Pin 8: Exp: 10v; Actual: 350mv

I'm inclined to think the issue with the tube, but when I put it through my tube tester, it came through fine at every check point.

I'm inclined to think it's my tube, but then if that's the case, I'm wondering why I got a false positive with my tester? Is there anything else you think I should look at?

Thanks all!

BR


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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 16, 2019 4:58 am 
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Most emission tube testers just use the cathode and grid. The grid is used as the plate of a diode and the tube is checked to see how much current flows.
So the plate could be shorted to something and the tube tester would not notice that. But such a short seems somewhat unlikely.

The voltage on pin 6 (the plate) being low would explain the other voltages being low as no current would be flowing to the cathode.

Try this. Pull the 6DR7 and then see what voltage shows up in pin 6 of the socket. If the tube is shorted then the voltage on that pin should come back.
If the voltage does not come back then you will have to find out why not. Either something is shorting the voltage to ground or the resistor feeding pin 6
from the B+ has a problem.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 16, 2019 5:13 am 
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Thanks for the tip Tom! I tried what you said, and the result was a rather unstable reading that floated around 20-80mv. It looks like I have another issue elsewhere, but now I have a better idea of where to start looking.


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