On 2010-09-29, Bob Engelhardt wrote:
Pete C. wrote:
Absolutely those are SCRs or Triacs, you can see the control terminal in
the first picture on the #8 device. ...

Actually, those are 4 terminal devices - there are 2 control lines
(black & white) for each. What does that make them? Bob

For really high current SCRs (as these appear to be), it is
common to bring out both the gate (the control terminal) and a second
wire which duplicates the terminal to which the control is referenced,
usually the cathode on an SCR. This keeps you from having to run an
extra lead to the appropriate terminal for each (usually rather
isolated) control circuit.

Check out:

http://www.surplussales.com/semiconductors/SemiC-SCR.html

and scroll down to the SRC -TO-94 example, and you will see the twisted
pair of small gauge wires ending in ring terminals in addition to the
high current lead to a *big* ring terminal.

Enjoy,
DoN.

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