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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Fri 27, 2020 5:28 pm 
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Location: east canton ohio 44730
is there a name for this coil? Horizontal linearity , or width?
Update: ok I think thats L39 horizontal osc trans. in the under the chassis schematic it had a black beauty soldered to it. I was looking for it under transformers and not the coils list. I think it has an adjustment from the outside as well as the inside.
UPDATE: I tweaked the inside one. until I had adjustment either way on the horizontal shaft. Now when I click channels, it stays. I even turned it off waited a while, turned it back on and it took 5 seconds while warming up to lock. Took about 5 or 6 turns out to get it in the range of the horizontal hold shaft having enough adjustment either way


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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Fri 27, 2020 7:44 pm 
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Heres where it stands. Seems its not clear enough, like its washed out, and of course the sound has the hiss to it like somethings out of adjustment. fine tuning knob helps but this is the best it gets and this is on full volume too.
Sound is still dropping low or just plain dropping out. As usuall, clicking the channel back and forth brings it back but not always. sometimes i have to rotate the channel shaft very slowly then when the sound comes back, put it back on channel 3


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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Fri 27, 2020 8:13 pm 
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Location: east canton ohio 44730
I see why people are asking if this chassis has a relay. 9t256 does have a relay in its schematic


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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Fri 27, 2020 9:53 pm 
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On your set the sound is done differently than on newer sets. On newer sets the sound section grabs the 4.5 MHZ difference heterodyne between the video and sound carriers. This remains constant without regard to the precise tuning. Your set is what is called a split sound set. The sound and video are processed separately and the sound tunes like a FM radio tunes. You use the fine tuning knob to tune it. But your tuner is somewhat erratic because it needs to be cleaned.

To clean it you have to remove it from the set. You will have to un-solder some wires and resistors attached to the terminal strip at the back end of the tuner that sticks out trough a slot in the tuner case/shield. Then loosen the screws holding the tuner in the case and remove it. Now you can clean it

You do want to get the cleaner on just the switch contacts as much as possible.

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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Fri 27, 2020 11:16 pm 
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Location: east canton ohio 44730
Ok then I will remove it. Its been removed before because the solder joints are not very well done like the factory did....not that mine are good either :lol: Hoping this will fix the low sound issues but I doubt it.
First problem is finding out how to even remove it. I took plenty of wire pictures, everythings unsoldered but what to take apart or unscrew with out the whole thing crumbling into a million pieces
TUNERS OUT


Last edited by quartermilecamel on Nov Sat 28, 2020 12:00 am, edited 1 time in total.

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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Fri 27, 2020 11:48 pm 
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Looking at the top of the tuner there are two screws at the back end of the top plate. Loosen those. Then at the very front of the tuner on each side of the outer case/shield there are some screws. I think two on each side. As I remember it, if you take those out the tuner will come out in one piece.

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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Sat 28, 2020 12:34 am 
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TUNERS OUT tested resistors I could get at......as usuall, the low ohmage ones are double out of tolerance or more so will replace those


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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Sat 28, 2020 12:46 am 
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Be Careful not to move any of those air-wound coils.

In the RF amp there are two bias resistors - usually about 820k, 1m or thereabouts. Make sure you find and check them.

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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Sat 28, 2020 1:01 am 
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820k gray red yellow....looking

i dont see 820k, well I dont see 820k in the tuner
R113, 108, 101, 95, 94, and R37 are 8200 ohms. tuner according to schematic doesnt have these
reread that post. 820k to 1M ok..........looking in rf section


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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Sat 28, 2020 2:20 am 
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When replacing parts in the tuner try to make sure that the new ones are in exactly the same physical location with the same lead lengths as the originals. And some of the resistors may be 20% tolerance. Don't replace anything that you do not have to. Tuners are touchy about stray capacitance and any two conductors form a capacitor.

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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Sat 28, 2020 3:50 am 
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The largest resistors in the tuner are 100K and they are on the oscillator. Schematic available here: https://www.earlytelevision.org/pdf/rca ... s_74-8.pdf


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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Sat 28, 2020 4:05 am 
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If you have a capacitor checker that can test for leakage at rated voltage, test every new one before installation. I have been doing that for years.

The little can in the vertical section on the 630 and later sets is the vertical oscillator transformer. Yours is apparently still good, but sometimes they open up.

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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Sat 28, 2020 4:30 am 
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Location: east canton ohio 44730
got it. Yeah replacing anything in this tuner isnt too thrilling for me


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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Sat 28, 2020 5:21 am 
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I always try to avoid replacing parts in tuners. As was pointed out, resistors can be 20% out (or more even), and the tuner will work just fine.

I was wrong about those resistors, that's for a later model tuner. Yours has a pentode RF amp.

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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Sat 28, 2020 2:31 pm 
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Ok cool on the resistor 820k. The only ones that seem to be out anyway are the very low ohmage ones. 47 ohms and the 150 ohms. all of them are double their original values, just like in the main chassis. Replace or leave alone. They are not too hard to get to, and they are not close to inductors. Major brain surgery required for the other ones.


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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Sat 28, 2020 2:34 pm 
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Location: east canton ohio 44730
Tim Tress wrote:
If you have a capacitor checker that can test for leakage at rated voltage, test every new one before installation. I have been doing that for years.

The little can in the vertical section on the 630 and later sets is the vertical oscillator transformer. Yours is apparently still good, but sometimes they open up.
well I do have a cap checker with magic eye and also the 8 dollar lcr checker off ebay. The cap checker I havnt worked into my normal testing practice yet. Looks like its time to start.


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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Sat 28, 2020 6:14 pm 
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quartermilecamel wrote:
Ok cool on the resistor 820k. The only ones that seem to be out anyway are the very low ohmage ones. 47 ohms and the 150 ohms. all of them are double their original values, just like in the main chassis. Replace or leave alone. They are not too hard to get to, and they are not close to inductors. Major brain surgery required for the other ones.

The ones that are double their correct values should be replaced. Even though they are not close to inductors, try to maintain the original physical position and lead length.

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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Sat 28, 2020 6:38 pm 
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You may not be able to get the sound as loud or noise free as you can on newer sets. At the time your set was made, TV stations broadcast a higher power sound carrier relative to the video carrier than they did later. The modulators in VCRs, digital converter boxes and such tend to duplicate what TV stations did most recently. Your set was designed expecting the higher power sound carrier.
Also the way modulators generate the sound carrier can be a problem. They generally directly create the video carrier and then generate the sound carrier from that by heterodyning it with a 4.5 Mhz oscillator. Now sometimes the video carrier is generated digitally and is somewhat noisy relative to what you would want for FM sound. That makes the sound carrier noisy too. The video will not care about this. And a newer set that uses the 4.5 Mhz intercarrier sound system (uses the 4.5 Mhz beat between the sound and video carrier) will not see the noise. But your split sound set will see it.

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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Sat 28, 2020 10:50 pm 
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so when it recieves z88 fm its super loud when turned full volume, yet the d to a box not so loud...........until the sound goes soft or out, (insert channel knob clicking to bring it back). going to try an amplifier


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 Post subject: Re: Just purchased a rca 9t246 for 100 bucks with stand
PostPosted: Nov Sat 28, 2020 11:10 pm 
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When receiving the FM station the set will see no video signal and the automatic gain would run the IF strip at a high gain.
Also, FM stations modulate the carrier over a wider range than TV stations or modulators do. That will make the FM station louder.
Hopefully after you clean the tuner, wiggling the channel selector will no longer change the tuning.
Some people cheat. They install an audio input jack on the TV and wire that to the volume control. Then they connect the audio output of their signal source to the TVs audio input. Opinion varies as to how evil this is.
Some older TVs have a continuous tuning tuner that covers the FM band. They can be used as an FM radio as well as a TV.

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