The KM-56 employs nickel diaphragms which are very difficult to obtain. If you need a replacement KM-56 head, I have one. It is "new old stock" still in the original box, never installed. You can email me at Fletcher@mercenary.com
if you're interested in this part.
I think you'll find the mics to be wonderfully clear, and exceptionally deep sounding. I have used them everywhere from vocals to acoustic guitars to one of two mics employed to record a drum kit. I've used them on loud guitar and bass amps as well as for strings, congas and pianos. A wonderfully diverse microphone with a sense of space and dimension rarely found in any microphone at any price.
Best of luck with it.