[sdiy] Difference in 2SK30, 30A, 30AY, 30 ATM, etc

[aankrom]

I think "ATM" just stands for the little package instead of the classic 
TO-92. What you should look for is 'O', 'Y', or 'GR': this is the IDSS 
classification, the amount of current that flows between the Drain & the 
Source when zero voltage is on the Gate. This is approximately 
comparable to hFE in bipolar transistors. I really have never known the 
advantages of having a high or low IDSS in switching applications. I 
think with an amp, a higher IDSS is better for gain. I could be wrong. 
Different manufacturers may use other codes than the "color name" codes 
(that's what _I_ call them...).

Check out this link maybe: 
http://www.diystompboxes.com/smfforum/index.php?topic=85270.0