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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 23, 2019 7:02 pm 
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Unlikely. Resistors set the working points on the tuner tubes, but it's the caps and inductors that set the operating frequency.

Does anything happen when you change channels ? Any crackle from the speaker or change in the snow pattern ?

If not, make sure the little coax going from the tuner to IF board is making good contact. Similarly make sure the IF board is connected to the main sweep board correctly.


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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 23, 2019 7:40 pm 
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I will add a few thoughts.

It is easy to affect the alignment of the tuner if you do any work in the tuner. The exact position of everything is critical. But a misaligned tuner will almost always give you something, sometimes with the channel selector set one channel higher or lower then where you would normally set it.

Tubes, especially when used at high frequencies, can fail to work in the set even when testing good on a tube tester. The oscillator tube in the tuner is one that can have that problem. So if you can not find anything else wrong, try another tube.

If you see snow, unless it is very faint snow, the RF amplifier in the tuner has to be working.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Tue 23, 2019 9:15 pm 
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I'll go through and check out my tubes on the set. Boy does the Philco set make it hard for you to test some of them, they bury the pins!


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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Wed 24, 2019 3:03 am 
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When we last left my 10L43 Predicta,I was getting snow, but no sound or picture. I'm going through the whole tuner to try and source out what may be the problem, and I think I may have found something.

I started by checking the baluns for the 300 ohm antenna input. One balun checked out and had continuity to the ground. But the other...nothing, meaning I've got an open somewhere in the coil between the balun and the ground.

So this may be something, but being the novice that I am, I'm still at that point where I can find problems, but I don't quite know what they mean. Could this perhaps explain my lack of picture or sound reception?

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Wed 24, 2019 3:50 am 
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And I found the break, toward the bottom of the pink colored antenna coil. Think this should be pretty straightforward to rewrap with some copper wire of a similar gauge?

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Wed 24, 2019 4:54 am 
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You sure are having problems with broken and missing parts that hardly ever have problems.

The broken coil could prevent any signal from your source from getting to the first tube in the tuner.

You should be able to rewind that coil. Note that it is probably wound with 2 wires wound together and you would have to be sure to get the ends connected to the right places. You might well get away with unwinding one turn of each wire (if both are broken) and splicing the winding back together. Again making sure that you get the correct ends together. Note that the wire is going to be coated with some insulating coating such as enamel. You will have to gently scraps a little of that off in order to be able to solder the splice.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Wed 24, 2019 5:23 am 
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Luckily only one wire was broken, the one which grounds the balun. I was able to unwrap it without disturbing the remaining good wire.

When I replace the wire, do I need to enamel coat it first to insulate it? The core itself has grooves in it for the wire to settle, so I wasn't sure if this would allow me to use bare copper wire which would be insulated by the groove.


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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Wed 24, 2019 3:11 pm 
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You should use enameled wire. Also, I believe there are two windings on that form which could make it a bit tricky to rewind. I'd try to fix the break if at all possible. Even if just temporary to get a signal into the set.


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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Wed 24, 2019 4:04 pm 
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If you can't get it, send me a PM. I have this pair in stock, if that's what your's calls for.


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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Wed 24, 2019 5:55 pm 
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Enameled wire is readily available. In fact I think that it will be much easier to get than bare wire of that gauge.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Thu 25, 2019 3:48 am 
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Brianruns10 wrote:
I'm still at that point where I can find problems, but I don't quite know what they mean.

Perhaps a little theory would be interesting.

As mentioned above, the coils and capacitors select frequencies. For any capacitor and coil combination, that combination will have a resonant frequency. You can change the resonant frequency by changing either the capacitance of the capacitor or the inductance of the coil.

A little more detail.

When an AC signal is applied to a capacitor, the current in the capacitor leads the voltage. When the voltage starts rising above zero, the current starts to flow heavily. When the voltage is nearing the peak value, the current has diminished quite a lot. If you apply a steady DC voltage to a capacitor, the current will fall to zero in a little while. A capacitor will conduct high AC frequencies almost as if it was a wire.

A coil behaves in the opposite manner. When an AC signal is applied to an inductor (coil), the current lags the voltage. When the voltage starts rising above zero, the current at first barely flows. When the voltage is nearing the peak value, the current is starting to flow heavily. If you apply a steady DC voltage to a coil, the current will reach a quite high steady state value. A coil will block (fail to conduct) a high frequency signal.

Now for a particular coil and capacitor combination, there will be a frequency where the two will have equal and opposite characteristics. That is the resonant frequency..

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: Apr Thu 25, 2019 4:41 am 
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A little on a different subject.

If you look at the schematic of the tuner, you will see a section called the oscillator and a section called the mixer.

The oscillator creates an AC signal of a desired frequency.

Now if you feed two signals into a somewhat nonlinear amplifier, the amplifier will create two new signals. One new signal will be a signal who's frequency is the sum of the frequencies of the two input signals. The other new signal will be a signal who's frequency is the difference of the frequencies of the two input signals.

The tuner uses this effect to convert the signal applied to the antenna terminals to the IF frequency. For each channel, the oscillator is set to run at the frequency that is the frequency of that channel plus the frequency of the IF strip. The output of the RF amplifier and the oscillator signal are run into the mixer. The mixer is that nonlinear amplifier. One of the signals coming out of the mixer is a signal at the IF frequency.

Now the main amplification in the set can be done by circuits running at a fixed tuned frequency.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: May Wed 22, 2019 5:02 am 
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Location: Kansas City, Missouri
Alright gang, I've been away for a little while, tinkering with the tuner for my 10L43 Predicta, and today I reassembled everything and hooked it back up to the chassis for a test. I hook up my signal pattern generator to the RF baluns and gave it a whirl. And the result was promising. I'm close, so, very, very close. I think there must be just one thing I'm missing, one thing overlooked. With your help I hope I can find it.

So what happened was this: when I powered up, I got raster, but no snow. When I tuned the set to channel 4 and switched on my signal generator, the raster promptly turned to snow! I fiddled with all my controls, but was unable to produce a picture. However, when I fiddled with the controls on the signal generator, like adjusting the RF attenuator, the snow changed in character as well.

So there is obviously signal being received from my generator. The tuner is doing *something* and on the correct channel. It's just not giving me a usable picture. Just snow.

Guys and gals, what say you all? Just what/where should I look next?


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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: May Wed 22, 2019 2:22 pm 
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Sounds like the oscillator is not running. Simple circuit, you should be able to find the fault.

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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: May Wed 22, 2019 4:30 pm 
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Thanks for the tip! Any idea which oscillator circuit, vertical or horizontal?


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 Post subject: Re: Predicta 10L43 First Powerup...squashed raster
PostPosted: May Wed 22, 2019 6:43 pm 
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I believe he is referring to the tuner local oscillator.
If the vertical oscillator wasn't running you wouldn't only see a horizontal line. If the horizontal oscillator
wasn't running the screen would be black, (no high voltage).
The problem might also be in the IF circuitry.

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 Post subject: Re: Predicta 10L43 [Edit: Update]
PostPosted: Jun Sat 01, 2019 6:07 am 
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Okay gang, I've got another update with my 10L43, a TV that is hell bent on resisting all efforts at resurrection, that just wants to remain dead. Well I keep fighting it, and inch by inch I've made progress. I've done further work on the tuner, and I've gotten the first semblance of an actual image! But the image I've gotten is a heck of a puzzler.

So I'm using a signal generator that outputs a variety of calibration patterns, including bars, dots, lines either horizontal, vertical or both in a grid pattern, etc, etc.

I hooked up my geneator to the set, and began to adjust the controls on the chassis, as well as the generator. And I got an image...sort of. Below is a shot of the screen.

Image

There's a great deal of noise, but you can clearly see a series of horizontal white lines. They are stable and most definitely an imagine from the generator, as they disappear when I shut it off, or change channels.

The problem is, the generator is set to out put a grid. I should be seeing vertical as well as horizontal lines. And when I toggle to other image outputs, like dots, or just vertical lines, they disappear. {below is an image of the various signal outputs I can choose from:]

Image

So I'm only getting an image when there are horizontal lines, and if there are vertical lines, they don't appear. I'm only getting half of the image I should be. It's really baffling.

What say you all? Where should I look next?

Thanks all!

BR


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 Post subject: Re: Predicta 10L43 [Edit: Update]
PostPosted: Jun Sat 01, 2019 1:44 pm 
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Location: Lawrenceville, Illinois 62439
To me (and I haven't worked on a tube TV for 30+ years), it looks like your horizontal hold is way, way off.
Dan


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 Post subject: Re: Predicta 10L43 [Edit: Update]
PostPosted: Jun Sat 01, 2019 3:37 pm 
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Location: Dallas, TX
Because a TV image is scanned horizontally the vertical lines in a grid (crosshatch) are very brief pulses on a scan line. With the horizontal scan frequency off so much the vertical lines are smeared to the point you can't recognize them. Dots are the same case. Get the horizontal frequency right and sync up and you should be able to see what you are expecting.

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


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 Post subject: Re: Predicta 10L43 [Edit: Update]
PostPosted: Jun Sat 01, 2019 3:53 pm 
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Location: Dallas, TX
There is something additionally going on, the screen look like the problem is not only the horizontal frequency.
Maybe the yoke is rotated causing the lines to slant more than they should. I wonder about the horizontal being off so far, I would think the H.V. would be effected more. I suppose the vertical frequency is off also.

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