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Old 16th Feb 2020, 11:25 am   #159
julie_m
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Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
Default Re: Grundig TK 819 Any Useful Info

There is a popular misconception about burning out tape heads by testing them for continuity. On the face of it, this is absurd: look what the bias oscillator is delivering into the windings during recording!

But there is a grain of truth in there somewhere. You do need to be a little bit careful with tape heads, but for a different reason.

If you test a tape head for continuity with an analogue multimeter, you can leave some magnetism in the core. You will then need to demagnetise it before using it again, otherwise your favourite tapes will get quieter and quieter with every listen as they are being partially erased. In the days when replacement tape heads were still readily available, this would have been worse (especially as it's hard to notice until too late).

A modern digital multimeter will use a much lower test current than an analogue one, which will not be sufficient to reach the edge of the hysteresis loop and so not have any permanent effect.

If you test a tape head for continuity with an AC bridge, there won't be any remaining magnetism anyway.

If you demagnetise your tape heads on reassembly, you will be fine.
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