Electronic – Replacement Transistor for Ultrasound Cleaner


I'm trying to repair the generator board on a Sonix IV ultrasound cleaner. I need to find a replacement for a transistor (in a TO-3 package), but the manufacturer uses an in-house part id, so I'm trying to figure out what kind of transistor this is.

This guy has a similar problem, but a slightly different generator board:
Replacing a transistor when I can't find any info on it. I suspect it is the same transistor though. Like him, the manufacturer is unwilling to give information about the part.

I have tracked the part-placement and wiring on the board, and created a schematic. Can anybody use this to suggest a suitable replacement part?




Top layer PCB:
Top Layer

Bottom layer PCB:
Bottom Layer



Best Answer

I am a former employee. It is an NPN High Speed switching transistor (similar to a BUV48A in a TO3 case). Any high speed switching NPN transistor with a rating of at least 600v, 15 amps, with a low hfe should work. You will also need to check the diode closest to the transistor, because it ran hot and failed in this board version. Use an ultrafast 2 amp. Change the 1 ohm resistor (R2) to a 24 ohm 3 watt, and change the 56K resistor closest to the 1uf 400v Capacitor (R4) to a 100K 3 watt. You may need to change the turns on the feedback (toroid) transformers, depending on the output waveform. One full cycle of the output on the oscilloscope should be approx. 16.4usec (~60khz). Measured from the Emitter to the Collector. The "on" and "off" should be as close to symmetrical as possible ( 8.2usec: 8.2usec). Approx 350vpp. The turns on the toroid should be 10T and 4T in general. I suggest using a 2amp GMA pigtail fuse instead of a 1 ohm fuseable resistor.