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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 21st May 2024, 7:16 pm   #21
Sideband
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Default Re: Grundig TK 144 - undocumented 6.3V fuse

In case some are not aware, fuses can 'age' and fail with no apparent cause. Consider a fuse like above in a heater circuit. When the heaters are cold, the total resistance is low so the switch on current is higher. As the valves warm up, the heater resistance increases (positive temperature coefficient) and the current is lower. After some years of this switch on stress, the fuse wire can become weakened and eventually just break (rather than blow). No fault, just ageing and a replacement fuse will restore operation.

In some circuits, you can see the fusewire within the fuse actually 'sag' at switch-on. Eventually something will give!
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Old 22nd May 2024, 8:12 pm   #22
DMcMahon
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Default Re: Grundig TK 144 - undocumented 6.3V fuse

Quote:
Originally Posted by Julesomega View Post
Quote:
Originally Posted by DMcMahon View Post
My extra fuse is 250mA, so different value from the 2A value from Post 1
That would be enough for the meter bulb but not much more
As stated in Post 14, the 250mA fuse had at some time previously blown and been repaired by having fuse wire of an unknown rating soldered externally across the fuse end caps.

Out of interest tonight I measured the current flowing through the fuse, at cold switch on it peaked at 1.5A and dropped down fairly quickly to 1.01A

David
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Old 23rd May 2024, 12:21 am   #23
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Default Re: Grundig TK 144 - undocumented 6.3V fuse

In that case, the extra undocumented fuse must have been installed with the wrong value, so it's odd that instead of going back under guarantee someone has bodged it with a wire link
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Old 23rd May 2024, 7:49 am   #24
DMcMahon
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Default Re: Grundig TK 144 - undocumented 6.3V fuse

Yes it is strange. Maybe the recorder originally had the correct 2A fuse fitted, which at sometime later failed (maybe due to age as per Post 21) and the owner fitted the 250mA (maybe that is all the owner had to hand) which of course it would have blown straight away, so did the bodge repair.

We will never know of course the real facts.

David
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