Hello, I recently acquired a Fender Tremolux amp. However its not working and only a little hum is heard from the speaker cab. I have tested all the tubes in other amps that I own and they continue to work with the Tremolux's tubes installed. I was thinking about replacing all the capacitors but really dont want to replace original parts if its not necessary. The circuit looks to be made up of only caps and resistors. How can I check if these are working? Thanks.