[ARC5] Interesting occurrence...
Bob Macklin
macklinbob at msn.com
Sat Apr 2 12:35:36 EDT 2011
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
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
More information about the ARC5
mailing list