[GreenKeys] Teletype REC11 Rectifier "is NOT suitable for use in the signaling ... circuits of Teletype apparartus"

[Ralph Irish]

Doug

The replacement recommendation for these "COMPUTER GRADE" capacitors is based on how long they
might last after being inactive for some time, whether the electrolyte is adequately 'reformed'
or not.  That is  NOT  a safety issue from the environmental standpoint.  I've never seen any
environmental warnings about how these items should be disposed of.  

Oil filled units from early 60s and before need attention and proper disposal.  There may also
be some legal consequences for 'random disposal', whether one is familiar with the EPA and other
agencies' requirements or not.  PCB oil is a great electrolyte and coolant, but nasty almost
forever, if just dumped into a landfill.  

A rep from one company we dealt with described one method of disposal, and if I remember right,
it involved a very tall smokestack with fire jets every so many feet, to burn and reburn the
oil fumes as they passed up the stack.  Allegedly, enough of this would produce some safe
residue.  One bad part of this method is that there are some circumstances where improper
disposal of PCB can create that stuff called "PHOSGENE", better known as Mustard Gas, from the
first World War, and those years.

That same rep gave me hell for opening that transformer that failed, to look inside the oil
compartment.  He said that if there had been any internal arcing, that some of that  PHOSGENE
gas could have escaped into the atmosphere.  Since I'm still here, almost 20 years later, I
guess that didn't happen.  After that, I became a long distance observer when these guys were
in the plant.  I figured I could always call for help if something happened!

Ralph - W8ROI

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On Nov 20, 2017, at 12:47 PM, Jones, Douglas W wrote:

> On Nov 20, 2017, at 11:24 AM, Ralph Irish wrote:
> 
>> After seeing a number of references and replies about the 'oil-filled capacitor', I am surprised that no one made mention of the possibility of dangerous 'oil' in these devices?
> 
> In the PDP-8 restoration community, this problem has been noted by David Gesswein:
> -- https://www.pdp8.net/shows/vcfe07/pics/dscf0037.shtml
> 
> These capacitors are commonly found in the ferroresonant transformer circuits of DEC computers built in the 1960s and early 1970s before the change to switching power supplies.  Ferroresonant transformers do the voltage regulation with clever magnetic circuits and a special secondary winding that powers just a capacitor, tuned to resonate at the AC frequency.
> Gesswein recommends replacing the capacitor in this circuit:
> -- https://www.pdp8.net/straight8/ps_restore.shtml
> 
> Michael Thompson of the Rhode Island Computer Museum has also commented on this: "all of the resonating capacitors in the PDP-8 systems at the Rhode Island Computer Museum failed, some spectacularly. We also recommend that you replace them."
> 
> So, I did:
> -- https://homepage.cs.uiowa.edu/~jones/pdp8/UI-8/log2014a.shtml#2014-03-27
> 
> 		Doug Jones
> 		jones at cs.uiowa.edu

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