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.
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.
The upper is bipolars, lower is FETs.
2SK is J-FET or MOS-FET.
the digits following "2SK"shows original part-number for every manufucture.
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)
In the case of TOSHIBA,
The alphabet added to the end expresses an Idss ranking.
You can specify it certainly.
See PDF of 2SK30ATM...
GR: 2.60-6.50 [mA]