[Vintage-Audio] Re Glass Heads

[wolfbob]

A glass head is not glass. It is a ferrite rather than a metalic core and
has windings just like a metal head. What they found was that on the ferrite
heads the gap would erode rather rapidly due to friction and heating with
the tape motion knocking off minute chunks of the ferrite. So Akai and soon
others found ways to coat the ferrite with a very thin layer of glass that
would bond to the ferrite and had the correct temperature coefficients etc.
and took the wear to almost nothing.  However the gap still erodes. The
erosion is a wear that is manfested in the reduction of very high frequency
response rather than the groove wear that is the case for metal heads. The
trailing edge of the gap just removed, making the gap wider and the
frequency response less. I have often found a new GX-747 that will go to 3
dB down at 34 kHz and those more worn that will do 18 kHz. The degradation
is gradual and in both channels at the same time and quite un noticable
unless you are a golden ear or a bat.

WBob

----- Original Message ----- 
From: "Duane Fischer, W8DBF" <dfischer at usol.com>
To: <vintage-audio at mailman.qth.net>
Sent: Thursday, August 05, 2004 1:20 PM
Subject: [Vintage-Audio] Re Glass Heads


>
>
> Because audio tape depends upon magnetic arrangement of the ferrite
particles,
> how does a 'glass' head do this when it is not a conductor?
>
> Duane W8DBF
>
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