Tube television reception

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berkeman

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It never did didly swat
And maybe this is why it didn't seem to do much. If you try to use it to improve the picture right away, that's not what it was for. It was to keep the picture tuned well as you watched the same channel for a while (especially right after you turned the TV on and the tuner circuit wasn't warmed up yet).
 
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That is my impression, although I've never designed that particular kind of circuit (I've designed PLLs, which are a related type of circuit though).

My impression from the Wikipedia article is that the feature is used to help stabilize the tuner's lock-in to a channel once is is tuned well. It helps to prevent drift of those old tuner circuits with temperature and time as you stay tuned to the same channel. So I'm guessing (somebody find the old manual please?) that you would change the channel knob to the channel you wanted, turn the Fine Tuning knob to get centered on the broadcast signal, and then turn on the AFT/AFC.

As long as the TV was still turned on, that would help to keep the TV tuned right on the frequency of that chosen channel. If you wanted to change channels or if you turned the TV off and later turned it back on, you would need to do the fine-tune knob (with AFC off) again first, and then re-engage AFC. But that's just my educated guess, unless somebody can remember better or find an old TV manual...
 
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I really appreciate the dialog. It wasn't;t explained to enable after a fine tune. It's a bit nostalgic to ask what did that 30 year old tv button do. But shoot the people that knew maybe thinning.. Thank you 😊😊😊
 

Averagesupernova

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I have to dig in some old television/video books but I suspect the AFT was a form of PLL. Probably compared the IF signal against a 'standard' xtal oscillator in the TV set. I won't say any more until I can verify.
 

berkeman

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Averagesupernova

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I didn't find what I wanted in my TV systems/video book but I will mention a few other things.
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I didn't think the day would come when I would have to explain how a manual TV tuner worked but here goes:
Suppose I turn the selector to channel 4 and dial around the fine tuning control to make the picture come in nice and clear but then decide channel 4 is broadcasting crap so I turn to channel 10. Now again I need to adjust the fine tuning but alas, it turns out that channel 10 is spewing out even more crap so, back to channel 4. I will NOT need to readjust the fine tuning. Each channel has it's own tuned circuit with an adjustable element. Fine tuning one channel does not affect the fine tuning on a different channel. You are actually tuning different components.
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Where AFT comes in is correcting for drift over the temperature range while the receiver warms up. If it is turned on it will take care of frequency drift within reasonable specs. I know that cable companies in the past have shifted the carrier frequency from 'standard' on some channels to avoid some interference. AFT will take care of this.
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Here is a link to a tutorial in PDF form for piece of test equipment used to service older TV sets. It includes a quick test for the AFT function of a TV receiver.
 
Summary: I had an old dial tune TV set. Obsolete now.

It had a small button that I think was suppose to improve reception. What did that button do physically?
My guess, is the button.. bypass or applies the fine tune-if it be auto or knob adjusted...
 
Welcome to the PF.

Did you read any of the posts in the rest of this thread? Or just the first one... :smile:
Sorry i just replied to the first question. I scrolled through the posts. Didnt see anything lf bypass /engage button.. sorry if i missed it. I registered just now as i recognise a gold source. Im still to fill oit my profile.. apologies, i dont get offended.. if im ever in the wrong. Just tell me... i like to be wrong, it the only possible condition to deliver true learning. No game of ego confirming for me. Shoot me Down at every sight... theres nothing greater. Nice to meet yall, sorry. I know this isnt the right place.. ill go intro in rhe correct section.🖖😋
 

berkeman

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No worries, we're glad to have you here. Enjoy the PF! :smile:
 
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Summary: I had an old dial tune TV set. Obsolete now.

It had a small button that I think was suppose to improve reception. What did that button do physically?
it was used to set the brightness
 
From 1968 to 1988 I was a TV repairman...now called a Home Entertainment Electronics Technician...Big Deal! The button was most likely a built-in degauser to remove any magnetic distortion of color on the screen. Just moving the TV from one wall to another could change the magnetic field requiring degausing (I forget proper spelling). We had a magnetic loop about 12" diameter we moved around in front of the screen as we slowly backed away. Color TV made Black & White images by mixing proper amounts of Red - Blue- Green for what was called a proper grey scale. Any thing with an electric motor could magnetize the screen and most had a built-in degauser that worked each time the TV was turned on. Shutting off a vacuum cleaner in front of the TV could magnetize the shadow mask just behind the CRT face. It was fun when the TV had rabbit ears and I moved my hand like magic around the antenna to block the sync-pulse...causing the picture to roll or flip. Then moving my hand away caused things to lock back in sync. To kids it was magic. I graduated from Elkins Institute in Dallas where Rush Limbaugh went. He studied Radio Broadcasting "D J" while I studied repair. He is worth many millions and I have a few bucks in the bank. Hind sight is definitely 20/20.
 

dlgoff

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What you said:
As long as the TV was still turned on, that would help to keep the TV tuned right on the frequency of that chosen channel. If you wanted to change channels or if you turned the TV off and later turned it back on, you would need to do the fine-tune knob (with AFC off) again first, and then re-engage AFC. But that's just my educated guess, unless somebody can remember better or find an old TV manual...
 
There was an AFC (Automatic Frequency Control) button that locked the channel to a pre-set frequency. There was also a pre-set 'picture' button that locked brightness, contrast, and color intensity to a pre-set level. Before PLL (Phase Lock Loop) things tended to drift, then very compact IC's (Multi-pin Integrated Circuits) came along and we had to adjust to making our body stay at the same electrical potential as the circuit. That required clipping a ground to our wrist and the chassis...which went contrary to previous safety precautions for electrical work. Body voltage, YES...ever walk across a carpet and get a shock when touching something metal? That could knock out an IC. Some could bias on with a 10th of a volt or even less. Some came plugged into a foam block that kept every pin separate from the others to avoid cross-pin voltage before installation. You electronics guys already know this and I got out of the business in 1988. So cut me a little slack. I know how fast things change these days.
 

George Jones

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I have another question. If I tuned that to channel 11 but l don’t have signal. What is displayed. I realize it’s static. But is the static the same channel to all without a broadcast?
Some the static was quite old, i.e., from 14 billion years ago.
 
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To the best of my recollection, there is a pure analog automatic frequency tuning (AFT) circuit that started to be widely used in many TV sets in the around 1970s until it has been replaced by digital AFT/AFC circuit in around 2000s.

It is certainly the principle of this pure analog automatic frequency tuning circuit is also based on the feedback theory.
 
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