[ARC5] Interesting occurrence...

[Dennis Monticelli]

Right you are, Bob.  The 5814A (not the plain 5814) is a "computer rated"
12AU7.  The 5963 is a quieter computer-rated 12AU7.  Dual triodes were
commonly used in logic circuits.

Other computer rated tubes were: 5844, 5915A, 5965, 6211, 6463, 5963, 5964,
5965, 6197, 6350, and 6887.  Manufactureres were predominately GE and RCA.
These tube types often show up in boxes of misc tubes FS and frequently as
NIB.  Because people aren't familiar with them they usually go begging for a
home.  This is sad because many are just improved versions of commonly known
tubes.  For example the 5844 is a 6J6.  The 5915 is a 6BE6.  The 5965 is a
12AV7.  The 6197 is a 6CL6.  etc.  Something to think about the next time
you rummage through an old box.

Dennis AE6C

On Sat, Apr 2, 2011 at 9:35 AM, Bob Macklin <macklinbob at msn.com> wrote:

> There was a special version of the 12AU7 made for this problem.
>
> Bob Macklin
> K5MYJ
> Seattle, Wa.
> "Real Radios Glow In The Dark"
>
> ----- Original Message ----- From: "Kenneth G. Gordon" <
> kgordon2006 at frontier.com>
> To: "Dennis Monticelli" <dennis.monticelli at gmail.com>
> Cc: "ARC-5 List" <arc5 at mailman.qth.net>
> Sent: Saturday, April 02, 2011 9:28 AM
>
> Subject: Re: [ARC5] Interesting occurrence...
>
>
>   On 2 Apr 2011 at 7:54, Dennis Monticelli wrote:
>>
>> Regarding leaving on filament without applied B+, there are some
>>> lessons from early vacuum tube computer circuits. In binary logic
>>> operations a tube could spend a great deal of time sitting at either
>>> an ON or OFF state. It was found that tubes were failing bofore their
>>> expected MTBF and that problelm was traced to tubes that had been in
>>> the OFF state for an extended period. This premature failure was
>>> nick-named "sleeping sickness"but is more correctly termed "cathode
>>> interface resistance." The mechanism is the formation of an interface
>>> layer between the nickel cylinder (in an indirectly heated cathode)
>>> and the active oxide coating. The series resistance of this layer
>>> reduces the gm. Thework-around is to run a little plate current during
>>> the "idle" state or better yet use a tube purpose built for the job.
>>> There are tubes in the premium industrial series of minatures that are
>>> specifically rated for computer use. These types are virtually immume
>>> to the formation of the problematic interface layer.
>>>
>>> In view of this known problem it wouldn't seem to be a good idea to
>>> run indirectly heatedfilaments over extended time periods without some
>>> trickle plate current.
>>>
>>> Dennis AE6C
>>>
>>
>> Dennis:
>>
>> I worked "in computers" for almost 30 years at the University of Idaho,
>> and I
>> "vaguely" remembered something like that...or at least it was yeasting
>> around in the back of my memory banks. That was probably why I asked.
>>
>> Thanks for the refresher. :-)
>>
>> Ken W7EKB
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