Tube television reception

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  • #1
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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?
 

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  • #2
HallsofIvy
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"Tube"? How old was it? The button is probably a "degausser". Theoretically it removed any secondary magnetic field that could build up on the screen. I don't think it was ever clear how useful that was,
 
  • #3
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It was from the late eighties
 
  • #4
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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?
 
  • #5
berkeman
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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?
Button or dial? It was common to have a "fine tune" dial control on those early sets, since they did not have frequency synthesizers and other ways of making very accurate frequency adjustments.
 
  • #6
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Button or dial? It was common to have a "fine tune" dial control on those early sets, since they did not have frequency synthesizers and other ways of making very accurate frequency adjustments.
Dial. It had a button that when pressed it would latch. It did have the fine tune knobs
 
  • #7
berkeman
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Dial. It had a button that when pressed it would latch. It did have the fine tune knobs
"Well, which is it young feller?" (Quiz Question -- what movie is that from?) :smile:

The "Improve Reception" control was a fine-tune dial or a single push-button?
 
  • #8
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I don’t recognize the quote. But it is humorous.
It had the push to fine tune wheel around each dial. But it had a three position push button. Well old timer what do you think the change was. It never did didly swat. I’m interested in what it was. The Degause was a one press and done. This set had intermediate position on the button
 
  • #9
berkeman
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I don’t recognize the quote. But it is humorous.
:smile:
Well old timer what do you think the change was. It never did didly swat. I’m interested in what it was.
My guess would be either a fine tune on the frequency, or a change in the AGC range.
 
  • #10
Averagesupernova
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Possibly Automatic Fine Tuning, AKA: AFT.
 
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  • #11
phinds
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It never did didly swat.
I assume that's a typo, yes? Or is there some part of the country where "diddly squat" is "didly swat" ?
 
  • #12
256bits
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I never knew a television that did have a de-gausser button on the unit, and I have known a few.
 
  • #13
DrClaude
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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?
It is whatever electromagnetic noise there is at the frequency of the channel. That noise will vary from channel to channel and from one location to another.
 
  • #14
256bits
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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?
So you were receiving VHF signals, channels 2 -13.
Any UHF channels 14 -69?
 
  • #15
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I never knew a television that did have a de-gausser button on the unit, and I have known a few.
Actually, our first color TV back in the 70's had one. It was a momentary contact button, and when you pushed it, the picture would jump and wriggle, as if it was a reflection in a pond you had dropped a pebble into. It would settle down in a couple of seconds, with possibly some change in the color. IIRC, it was supposed to counteract accumulated magnetization of the chassis and picture tube.
 
  • #16
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Actually, our first color TV back in the 70's had one. It was a momentary contact button, and when you pushed it, the picture would jump and wriggle, as if it was a reflection in a pond you had dropped a pebble into. It would settle down in a couple of seconds, with possibly some change in the color. IIRC, it was supposed to counteract accumulated magnetization of the chassis and picture tube.
As did my first trinitron computer monitor. Not sure its the switch in question
 
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  • #17
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But it had a three position push button.
A picture would help.
My humble bet is that it was the VHF/UHF selector.
I can't recall what was the usual third position. Maybe the composite input?
 
  • #18
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I'm sorry but the set went to the landfill for recycling. it had a UHF dial and fine tuner and a VHF dial with fine tuner that was much slower at adjustment. It had a volume knob. And below that was this rectangular small button. It was a Panasonic from the 80's. The difference to the picture was negligible however the physics of the reception would be interesting. on /off
 
  • #19
berkeman
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It was a Panasonic from the 80's.
A quick Google Images search on Panasonic TV 1980s turns up some possibilities. Here is the CT9010, which does indeed have an AFT button...

http://vintageelectronics.betamaxcollectors.com/panasonictelevisionsetmodelct9010.html
1568235065920.png


https://en.wikipedia.org/wiki/Automatic_frequency_control
 
  • #20
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Yeah that's basically it. Is there a digital complement?
 
  • #21
berkeman
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Did you read the Wikipedia link? It does mention what happened when digital frequency synthesis was introduced... :smile:
 
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  • #22
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Sorry if I got ahead of myself. I didn't see the Wiki link. Thank you. Is what I needed to read. Thanks
 
  • #23
berkeman
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I didn't see the Wiki link.
That's my bad. The link was kind of hidden at the end of my post after the picture. :smile:
 
  • #24
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If you can I seem to have narrowed it down a lot. on topic now. Is it a tracking function of some kind? Thanks for the kind correction on the wiki
 
  • #25
berkeman
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Is it a tracking function of some kind?
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...

Wikipedia said:
In radio equipment, Automatic Frequency Control (AFC), also called Automatic Fine Tuning (AFT), is a method or circuit to automatically keep a resonant circuit tuned to the frequency of an incoming radio signal. It is primarily used in radio receivers to keep the receiver tuned to the frequency of the desired station.
 

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