From: liz@poppyrecords.invalid.invalid
Cursitor Doom wrote:
> > >Just goes to show how a
> >> tiny bit of invisible foulage can throw a real spanner in the works
> >> for the unwary. Lesson learned!
> >
> >About 6 months ago I was asked by a local dancing school if I still had
> >the master tape of a show where I had done the sound 20 years ago.
> >After spending an evening sorting through piles of tapes stored in a
> >disused lavatory (Yes, really!) we found it. I laced it up on one of my
> >Ferrographs (Logic 7) and the sound quality immediately deteriorated to
> >rubbish.
>
> Knowing what I now know and never having handled 40+ year old tapes
> before, I can well believe it. The F'graph I recently had serviced is
> a Logic 7 as well, BTW.
I bought one that the BBC had scrapped because of a "Logic fault"
(according to the ticket tied to it). The problem was a very mysterious
intermittent one: sometimes pressing one button would give the function
of a different button - but sometimes it worked correctly. I kept a
note of the faults when they showed up and was lucky enough to obtain a
full service manual that had a table of logic faults included with it.
The table showed that the fault was coming from one of the relays not
operating - but when I watched carefully I could see the relay armature
moved. If I operated it by hand, everthing worked correctly.
Then I spotted the cause: a tiny iron filing was in the air gap -
sometimes the magnetism caused it to stand up on end, preventing the
full travel of the armature - but sometimes it lay down flat and
everything worked correctly. I removed it with a bit of adhesive tape
and was pleased to find I had bought an excellent machine in perfect
condition at a ridiculously low price.
>
> >We played the tape for long enough to identify that it was the correct
> >one, then I had to spend the following evening cleaning up the required
> >5-minute segment. I wound the of tape backwards and forwards through a
> >fold of soft cloth, picking up loads of debris at each pass.
>
> According to the nerds on Tapeheads, before we play an old tape we
> should bake it beforehand - yes, really - and digitize it upon first
> play then bin it for the sake of our machines!
It depends on the cause of the problem. That is the recommended way of
treating 'sticky shed' but if the tape is very old (and sticky shed
isn't the problem), baking it may cause it to become brittle and keep
snapping.
>
> >Eventually i was able to play it, stopping and cleaning the heads and
> >the guides several times. If you don't clean the guides as well as all
> >the heads, including the erase head, even a clean tape can drag
> >particles into the recording and playback heads. Finally I edited the
> >good bits together, burnt them onto a CDR and sent them to the dancing
> >school.
>
> Yes, you would have to do the entire visible/accessible tape transport
> mechanism or it won't have the desired effect for that reason. I find
> it unbelievable that heads that *appear* spotless can refuse to work
> properly until freshly cleaned again. How many picograms of crap does
> it take to mess things up? Can't be many!
I can't remember the exact reference but there were papers written on
this in the 1950s and 1960s. I would begin by looking in the Philips
Technical Review around the late 1950s and onwards. It became even more
important when tape was first used for digital and video recording
because it affects the high frequencies much worse than the low
frequencies.
--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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