Email exchange about the history of the plastic shells of the K2 series of octal plug-in amplifiers.
From: "Sheingold, Dan"
To: Robert Pease, Joe Sousa
Date: Tue, 9 Nov 2010 10:33:30 -0500
Subject: RE: Operational Amplifier Model K2-X
Not much further to say at this time, except re-
... the tan cases were somewhat flammable...
So were the black phenolic cases.
I believe the more recent grey clamshells were Lexan.
...Actually, I think we were also using better bias circuits on the Neons, that would keep them away from noisy regions...
I agree. The Seddon influence. Bruce greatly improved the rationality of our designs.
P.S. Permission on this thread OK
From: Robert Pease
Sent: Sunday, November 07, 2010 10:01 AM
To: Joe Sousa
Cc: Sheingold, Dan; Doug Coulter
Subject: Re: Operational Amplifier Model K2-X
*** Hello, to Joe, Dan, and friends, see comments at ***
On Sep 14, 2010, at 7:10 PM, Joe Sousa wrote:
"but Dan says that the brown modules had no radio active material."
he advice. I had a suspicion that the emissions in the neons would not be hot beyond alpha and beta. But I would like to sniff out my modules. I have a couple of neons that came out of a brown module
> At 10:30 AM 9/7/2010, Sheingold, Dan wrote:
> > Jimmy et al:
> > If the cases and sockets are black I think it's a good bet that
> > there will be 2 or 3 NE2s with dabs of radium paint. If the sockets
> > and/or the cases are beige, it's more likely that the neons have
> > internal radioactive material or gas.
> > Some of the very earliest K2-Xs may have had Thyrite (a material
> > with a nonlinear I-V curve) instead of neon coupling elements. No
> > radioactivity.
> > Bob and Joe:
++++++++++++++++ No comments on this; just for reference...++++++++++
> > The realization that we needed some form of radiant energy in the
> > darkness of the K3 bottoms to initiate ionization occurred before I
> > joined GAP/R in Nov '49 (at least 2 years before any K2s existed).
> > At that time, the K3 black boxes had a nest of neons between the
> > back-to-back circuit boards, with little swaths of radium paint over
> > them. Later there was a period when neon coupling was abandoned in
> > favor of Thyrite because the neons could be noisy or even oscillate.
++++++++++++++++ No comments above this; just for reference...++++++++++
> > But Thyrite didn't really have a steep enough I-V curve, and the
> > quality of the neons improved in later devices
*** Actually, I think we were also using better bias circuits on the Neons, that would keep them away from noisy regions.
> > We started with black Bakelite sockets,
*** and Plugs....
but they leaked too much
> > current from the -300-V terminal to the amplifier's adjacent
> > negative input.
*** This I believe.
The sockets transitioned to tan mica-filled
> > phenolic, then diallyl phthalate.
** We changed away from the tan, not for just color-matching reasons, but because the tan cases were somewhat flammable. If one overheated and caught fire, it would burn and melt and drip down flaming phenolic. And set its neighbors on fire. Maybe even the K2-W's in the rack below it.
This was first observed on an HK rack-full of K2-B1's, where the molten flaming phenolic ran down to other equipment. This was also related to the fact that in the old K2-B1, the heater-Kathode rating was exceeded grossly. The rating may have been 100 or 200 volts, but the kathodes were at 280 volts below the Heaters' ground bias established by the HK. After that, the data sheets had cautions to not run K2-B1's in the HK manifold unless you re-biassed the heater transformer to something like -150 vdc? I was not involved in this and don't recall the name of the less-than-happy customer. But we all heard about it.
The case color was changed to
> > adapt to the socket color change.
*** Actually, most of my recent K2-s have a different color for the plugs and sockets,
than the case per se. The plugs are darker grey than the case's light grey. I don't have OLD ones - but Joe does! He could run a census of (colors) vs. (date code). At VERY LOW priority.
Best regards. / rap / Engineer.