A: It is difficult to come up with a definitive answer to this question — it also difficult to come up with an empirical test; for example, pulling out the tubes and putting them on a tube tester won’t tell you what you need to know. To a large extent, the answer depends on how heavily you use the amp. If you use it lightly, a few times a month, the tubes may last for many years. If you run on “11” for eight hours a day, you might want to buy stock in a tube manufacturer.
Here are some tips:
- Preamp tubes tend to last much longer than power amp tubes.
- If the tube has turned white, it’s lost its vacuum and should be replaced.
- If you notice your amp is suddenly sounding weak, squeals, is noisier, loses high end, lacks sensitivity, loses gain, fades up or down, or otherwise changes in response or tone, it’s probably time to consider changing the tubes (or there may be a problem with the amp).
- If you replace one power amp tube, you should replace all of them.