[R-390] 5963 vs 5814

[Jim Haynes]

On Sat, 18 May 2013, Gordon wrote:

> I am confused as they both cross to a 12AU7 ?
>
A problem came up in early computers.  When a tube was cut off for a long
time, as in half of a flipflop, it would not conduct when the time came to
conduct.  The problem was traced to silicon as an impurity in the cathode
material.  This caused an insulating layer to form between the cathode
material and its metal sleeve substrate, so the cathode was disconnected
inside the tube.  The problem never occurred in applications such as
audio amplifiers where the tube is conducting all the time.

The 5963 and 5965 were specified for computer service and were more
or less guaranteed to be free of the silicon impurity and thus not
subject to the problem, which was called "cathode interface formation".
I don't know whether the later 12AU7s and 5814s were also made with
the high-purity cathode metal, after the cause of the problem was
discovered.

So it should be fine to use a 5963 to replace a 12AU7, but you don't
want to put a bunch of 12AU7s in your computer.