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.

 Also, re:

...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.