Hi: New to this site but not new to old radio service. It does indeed sound like the cartridge is bad, because touching the wiring at the back of the cartridge and getting hum does indeed indicate the amp is ok. You can find ceramic cartridges online at reasonable cost. My favourite supplier is myneedlestore.com. He is in Quebec and has some stereo ceramic cartridges available. The only problem is that generally ceramic cartridges put out from about 100mv to .5volt and crystal cartridges put out usually over 1volt. That may leave you with a lower volume when playing records. I have found this when I have replaced old defective cartridges. Hope this helps.