"Thyractors" on the DEC LT33 modified ASR33 Teletype

[Paul Koning]

>>>>> "vrs" == vrs  <vrs at msn.com> writes:

 >> I am currently modifying my Teletype ASR33 into a LT33 according
 >> to the
 vrs> DEC
 >> specifications to work with my PDP-8/L. Does someone know what is
 >> a Thyractor (GE 6RS20SP4B4) ? Some kind of voltage clamping device
 >> ?.  How could I make one, using, for instance a pair of thyristors
 >> or a pair
 vrs> of
 >> zenner diodes ?

 vrs> thyractor: "A marketing name by DAVIS, the thyractor was a
 vrs> combination of a low loss choke (the reactor) and a thyristor."

 vrs> I know NTE still markets a replacement for the 6RS20SP5B5 (but
 vrs> not the 4B4).  Unfortunately, I don't have the detailed specs
 vrs> for the 4B4.

 vrs> On the other hand, I think it is just a handy voltage clamp to
 vrs> keep the semiconductor circuits from seeing the inductive spikes
 vrs> from the TTY.  Shouldn't be too hard to come up with something
 vrs> else that would work.

If it's a voltage clamp, then either back to back zeners, or a MOV
should work.  MOV might be the better choice since they are explicitly
designed as protective devices.  Zeners would be ok in the larger
sizes, but the small ones may be fragile enough that they don't do
well in this application.

     paul