Hello all,I've been trying to find a cross-reference for an OEM transistor for a month now with no luck and thought I'd try here. The only reference to the elusive SIV300004 is one I found here in one of your UseNet archives. In that thread, the OP argued that the transisitor was not bearing an OEM or in-house number. I would disagree with that as the only place one seems to find the device is in a Sonix IV Ultrasonic Cleaner. The prefix "SIV" and "Sonix IV" are obviously more than just a coincidence.Anyway, I'm far from an electronics guru, but also am not a complete idiot. I was hoping someone could make an educated guess as to a replacement transistor from the info I can provide.The Sonix ST-144 has 120VAC going into a small Isolator or EMI/RFI Filter board (http://www.kabdental.com/small-dental-equipment/ultrasonic-cleaning-units/access15.jpg). The 120VAC coming out of that drives two SS8G-PCA120 oscillator boards (http://picasaweb.google.com/lh/photo/lW94RiELL4wFLEoNy_ZjRQ), one for each piezo transducer bonded to the bottom of the water tank. (There is a small torroid core wound with black wire that is difficult to see to the right of the larger transformer). I believe this circuit is almost identical to the schematic shown here: http://www.repairfaq.org/sam/samschem.htm#schahv5 Sonix literature states that this model cleaner oscillates at 60Khz. I believe the output to be in the 400-480 volt range. Now to expose my stupidity... would this be a PNP, an NPN, a MosFet? I need some sort of high-frequency, high-voltage, (low-gain?), device in a TO-3 can to replace these. Our cleaner sprung a leak and Sonix is completely unwilling to help. They wish to sell me complete boards at $125 each. (I did find them for $91 each online). The transformers test as neither open, nor shorted, the diodes test good (in-circuit), but the TO-3's do not test as good (out-of-circuit).Might anyone offer a best guess as to a semiconductor replacement that might save me a big chunk of change?Thank you very much.Paul