Questions about Ultrasonic Knife

Hello guys! -

I used an ultrasonic knife for many years until the power supply finally bit the dust. It's rated at 40KHz with an output power of about 30 Watts. Rather than to try and repair the power supply, I would like to replace it with a 40KHz power supply from an ultrasonic cleaning system. I connected the hand-held knife assembly (which contains the converter and sonotrode with a means for attaching an X-acto knife blade) but except for making a lot of irritating noise, the knife does not cut anything. Obviously the knife unit is not tuned to the power supply in some respect. So, my questions are, would it make better sense to try to mechanically tune the sonotrode rather than to electrically tune the power suppply? Am I wasting my time even trying to make the knife work with a power supply that was designed for an ultrasonic cleaner? The cleaner power supply doesn't seem to have any adjustable components inside it on the circuit boards, and so it's probably a fixed design. Any suggestions would be greatly appreciated. THANKS!