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Old 11th Dec 2021, 11:54 am   #7
Ted Kendall
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 3,087
Default Re: Are these Revox tape heads scrap?

Originally Posted by TIMTAPE View Post
Originally Posted by Ted Kendall View Post
...Incidentally, I think the quoted breakpoint was at 4mm...
Thanks for the correction, Ted.

Originally Posted by Ted Kendall View Post
...although I did use one set of heads far further than that - I had to admit defeat when the gap collapsed on one side of the playback head - at all but 6mm! Curiously, the head showed no obvious deterioration before that. I wouldn't bank on that sort of luck, though.
Yes I think I read somewhere years ago that a playback head increases in HF efficiency right up until the eventual opening of the gap, then it's all downhill, whereas a record head needs a certain minimum of metal remaining in order to fully magnetize the tape.
Agreed. As the polepieces get thinner and the inductance drops, both output and HF should, theoretically, rise. In this case they certainly didn't drop until the day the gap went phut. I remember also having Terry make some heads for a Telefunken machine which originally had Photovox heads. These worked well, but were about 6dB down in output. Terry concluded that this was because he had used thicker polepieces than Photovox, the upside being that his heads would have a longer life.
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