I'm busy repairing a guitar amp from '79 and stumbled upon these. They look like resistors, but they are definitely caps. I confirmed that with the PCB schematics and by measuring the ones with larger values, but I don't have the equipment to measure the ones in the pF range (e.g. the one in the middle should be 470pF). So I thought about replacing them, just in case. From what I found via Google, I suppose I can use ceramic disc caps as replacement. Is that correct? And is there a way to determine their maximum voltage rating?
Edit: Not sure if I may post the complete schematics, so I added images of the areas around the caps in question. The ones on the photo are C6, C8 and C5.