The original AL-80 (not A or B)is close to 20 years old. I bought one of the first and that was in '83 or '84. There were a couple of serious problems with that model, such as arcing bandswitches, that make it very undesirable. Haven't heard of any similar problems with the later models, and owned an AL-80B for some time with no problems whatever. You may need to purchase a new 3-500Z. If you ask the owner whether it shows full output on 10 meters, that would be an indicator of tube health. But - sadly - most guys wouldn't know how to answer the question. If possible, it would be a good idea to have a peak inside the pi-net compartment and see if there are any visible burn marks on the bandswitch or anything else. No telling how a previous owner might have abused the amp.