Japanese transistors

I found this info in a forum, it  clears up some of the confusion:

"Well,,, in Japan, "2SK30A" is a most common and very popular.
for low-frequency use, especially audio-use.

Its current part-number is 2SK30ATM. perfect substitute of "2SK30A"
TOSHIBA only carried out the minor change.

http://www.sm.rim.or.jp/~konton/Museum-7.htm
The minor change of "30A"was carried out in this way.
You'll notice the versions since 1970s.

Tons of data lists of Japanese transistor/FET also containing old things.
http://lobs.hp.infoseek.co.jp/data/data.html
The upper is bipolars, lower is FETs.

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2SK is J-FET or MOS-FET.
the digits following "2SK"shows original part-number for every manufucture.

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Japanese(or OEM) Bipolar-transisiter...
2SA PNP generally high-freq use, low-freq OK
2SB PNP low-freq
2SC NPN generally high-freq use, low-freq OK
2SD NPN low-freq
2SJ P-channel FETs (both JFETs and MOSFETs)
2SK N-channel FETs (both JFETs and MOSFETs)

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In the case of TOSHIBA,
The alphabet added to the end expresses an Idss ranking.
You can specify it certainly.

See PDF of 2SK30ATM...

 R: 0.30-0.75,
 O: 0.60-1.40,
 Y: 1.20-3.00,
 GR: 2.60-6.50 [mA]

Found here