The following was edited from an email exchange started by Jimmy Selph about the K2-W modules.

----------------------------------Friday, September 03, 2010 7:54 PM

Joe- I don't think that there are any radioactive materials in the K2-X. I copied Dan Sheingold and Bob Pease who were enginneers at Philbrick at the time that the K2-X was being made.

Bob-***   I   have  to  debate  that.  In   earliest  days,  we  used  NE-2's  which  probably  did NOT   have  any   radioactive  junk  in them.     But  when  we  had  little  problems  that  a  stack of  3  neons  did not  get  enough  voltage to  FIRE  very well ((in the  dark,  inside  the  K2-case,))   we  switched  to  NE-14's  that  _DID_  have a little  radon  gas  or  radioactive  paint, to insure that they would  fire.   I  can't tell you  when that  was,  but it  could  have been  1957+/-2?    I  bet  Dan  can make a  better  guess;  I  only  arrived in 1960.   So  if  you  want to see if you have a  K2-X  with  or  without  any  radioactivity,   sneak up on  them  with a  Geiger Counter  and  see what it says.   That's  the only way to tell,  for sure.

With  the  radio-active  materials,    they  could not  be  used in  Nuclear  Submarines,  which is why we  designed  K2-YJ's  and  K2-WJ's  for  such  military  work.  

[snip]

Best  regards. /  rap /  Robert A. Pease,  Engineer.

----------------------------------Date: Tue, 7 Sep 2010 10:30:09 

[snip] 

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:

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. But Thyrite didn't really have a steep enough I-V curve, and the quality of the neons improved in later devices.

 We started with black Bakelite sockets, but they leaked too much current from the -300-V terminal to the amplifier's adjacent negative input. The sockets transitioned to tan mica-filled phenolic, then diallyl phthalate. The case color was changed to adapt to the socket color change.

 Dan

----------------------------------Date: Tue, 14 Sep 2010 10:32:15

Joe: 

 "but Dan says that the brown modules had no radio active material."

 Any neons Philbrick used in K2s should be suspected of having a small amount of radioactive material (solids or gas) on or in them.

 The problem wasn't always insufficiency of voltage to fire the string; it was also inconsistency of firing. The radioactive material made certain that there was a ready supply of photons to ionize some gas molecules immediately, rather than having to wait for random photons or cosmic rays to set off the avalanche.

 Another interesting application of these painted NE-2s in the early '50s was as integrator clamp switches. NE-2 (and resistor) across the capacitor, and an RF coil wrapped around it. When the coil was energized (I think they used 1 to 3 MHz) the NE-2 conducted bilaterally and discharged the capacitor to zero. When the excitation was removed, the capacitor was free to integrate.

Dan

----------------------------------Wed, September 08, 2010 7:20 am

From: Doug Coulter

Date: Wed, September 08, 2010 7:20 am

I had been looking for those doped neons myself -- got a couple in the early years that are in my goodie box. They are quite rare in the collection -- they went to other "zener diodes" as described below and  if I recall right, away from the whole idea later -- too bad, as I've used that trick to make DC coupling multistage amps myself and the performance is better (on some levels).

The externally doped ones you can't miss, it's a big stripe of what looks like the same stuff they used to put on big ben clocks.

Neons rarely had anything radioactive inside too -- they came up with better ways quick. Often a fancy metal for the rods and some coating of rare earth or the alkali metals (same as a tube cathode). You'd never measure it if they did -- the glass is way thick enough to stop all the alphas and nearly all betas. Old ones would show hotter through the glass as the daughters are gamma emitters, most often.

The output in any case is nearly all alpha rays and many geiger counters won't see those, including those russian tubes -- we saw them cheap on ebay and looked up the specs. The little one tells you from a roengetn/hour up. In other words, starting sensitivity is at the point where you're getting a max daily dose (as defined in 1948! Things have tightened up a bunch since.) in 6 min. As in, if you see it reading at all -- run!

Anything that stops light will stop most alpha rays. The good geigers that can see them use a hyperthin window of mica, Be, stuff like that, and have a protector so you don't put your finger through it. I have a few, some with good tubes but broken electronics we might get rid of. (the electronics are a lot easier now than when most of these were made)

Of course, a hot alpha emitter will be making daughter isotopes, and those will give off beta and gamma. The beta usually won't make it through the opamp plastic.

That top kit they sell is probably better than nothing, but it's kind of a passive voltmeter based on a 10 ma meter, if you know what I mean -- very numb. *Everything* sees cosmics, that's not a big claim. I do that here with two sheets of metal spaced 1/4", about a kv, and a scope -- they are LOUD compared to natural sources.