Quicksilver amplifiers are designed to last a lifetime. They have simple circuits and use quality components. My QS Mini Mite mono blocks are 18 years old and still going strong. Bought them new from Mike Sanders in 2006. If you still enjoy the sound of your QS tube amplifiers I’d call Mike and arrange to have them serviced.
Getting them back to their original performance might be less expensive then you think. Best of luck 👍