[ARC5] Interesting occurrence...

[Kenneth G. Gordon]

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