Samuel M. Goldwasser wrote:
The closest I can find is for the C387 series found in a 1977 GE
datasheet, which is similar and fast and may be its predecessor, but
doesn't go up to anywhere close to the voltage I've been using it at
(!!) without problems.

Is this the data sheet you found?
http://www.datasheetarchive.com/dl/S...s-00102816.pdf
The charts at the top say 120 to 550 A, depending on the frequency, 2 uS
typical turn-on, 30 to 40 uS typical turn-off. The "N" in the part
number implies that it's an 800 V part. The flange on the top is 2.2"
diameter. It also talks about a "new high-frequency rating" for
rectangular pulses, but that seems to have more to do with current
and pulse shape, than voltage.

Some other sources say that the GE designation for the above data sheet
was "specification sheet 170.44".

Google Books has a few different versions of the GE SCR manual, but
they won't show the scans. I found a scan at (slightly munged)
www dot introni dot it /pdf/GE%20-%20SCR%20manual%201972 dot pdf
, but all it has on the C387 is a similar overview sheet to the two
documents above.

Matt Roberds