I’ve worked on tube gear for years, and judging by physical signs is not reliable. Especially with power tubes. Running a power or integrated amps on weak output or driver tubes risks damage to the amp. Amps with bias adjustments should be checked periodically. A significant change in voltage can be an indication of a tube in decline. For small signal tubes, the only truly reliable way is to use a tube tester. Ideally a Hickok or B&K. These can be expensive, but you can still find old Sencore "Mighty Mite" testers on ebay now and then for around $100 or so.
How do you know when tubes are done?
I have a homemade pre-amp and amp - both tubed.Recently, it became necessary to turn the volume up quite a bit to get the same sound level.It still sounds good but I started to wonder if a tube or two was the culprit. The tubes are about 8 or 9 years old and get light to medium use.
Suggestions?
Suggestions?