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Okay so I have a restored vintage TV set from the early 60s all tube and the thing is amazing not only from a historycall perspective
Now I have a problem, every time I trun on the thing the filament inside the crt tube light up like a light bulb at first but then dims doen and works OK
Now if the filament opened up the tv would be junk and I am a bit scared everytime I power it on the filament might go open circuit cause the first bright flash (every time its powered on )on the crt filament indicates the AC current bursts into the filament and then GRADUALLY evens out thru all the filament string which means that 1/4 part of the filament is at that point over-currented and it takes a second or two that the whole filament starts glowing and Im afraid that in that second the overloaded filament miht pop
I measured voltage is fine, also measured the current draw on the filament aslo fine and the transformer supplying it is a 6,3V 0.6 A
Now what I would like to achive is that the filament from the crt starts slowly glowing until it reaches its normal glowing,for example I tryed a light bulb in series to eat up that burdt of current and then slowly dim down to let the CRT filament take over but I havent achived it yet
if it were DC votlage this would be a lot easier, what I want is that the CRTfilament slowly starts glowing and takes a few seconds to warm up which is a lot better for the filaments life then instant on esspecially on a 50 year old TV set
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>>1031973
all Im trying to do is slowly power up a filament from a AC transformer
how to ?
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Put a resistor in series and increase the supply voltage to compensate for the drop across it. Filaments have low resistance when cold and high resistance when hot (15x difference for light bulbs, less for tube filaments). Resistors are designed to be as constant as possible. The resistor will block the inrush current but will end up not wasting too much power once the filament gets up to temperature.
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>>1032032
cant because if I use a different transformer then it wouldn't be original anymore and thats a big thing in vintage televisions
The filament is a 6.3V 600mA and the transformer is AC 6.3V 0.6A and I have to put something between them to ensure the filament starts to glow slowly and then lights up maybe like a capacitor that would charge when the filament would be powering up and then when its fully charged it would act as like it was a wire instead
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>>1032037
Maybe just add a bridge rectifier to the filament supply and do exactly that? Run the filament off DC with a huge tank capacitor.
On the other hand, maybe the original engineers knew what they were doing, and it's fine how it is.
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>>1031973
>every time I trun on the thing the filament inside the crt tube light up like a light bulb at first but then dims doen and works OK
>TV tech from the 90s.
This was pretty normal. There were some sets that had a standby pre heat voltage on the filament. Those tubes did tend to last well but I have never seen an open filament due to age alone. It was normally caused by a cracked tube letting air in.
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>>1031973
>the filament inside the crt tube light up like a light bulb at first
Normal for vintage / tube TVs
Google: filament inrush current limiter
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>>1032238
>filament inrush current limiter
could I use a thermistor in between them to achive this, but I think 6.3v is a bit low for a thermistor ?
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>>1032345
Yes you could.
On the other hand, like the others have already said: this "problem" of yours is something the designers of the TV didn't see as a problem. Most likely the same applies to the designers of the picture tube as well.
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>>1032350
I am too paranoid ,that it will eventually lead to an earlier filament failure
Im gonna use another vacum tube in series with it and a switch ,which is the best solution for now
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