root wrote:

I have recently been converting my RTR tapes to mp3
and have found a problem with tapes made by Ampex
for Philips or London, or under the Ampex name.
These tapes have a charcoal colored oxide. The problem
is the tapes chatter against the heads and emit
a loud screech which carries over into the output
signal. These tapes haven't been played in almost
40 years. None of the brown oxide tapes made by
other mfgs have a problem.

I have tried respooling the tapes and even tried
coating my heads with a silicone lubricant but
neither works.

I wonder if anyone has a solution. Most of
these tapes are unique.

Re-post in rec.audio.pro. You have classic polyurethane binder problems.
Don't attempt to play those tapes again until you take expert advice,
and you'll get it there.

Graham