I lived in Cape Town. I was buying Quad II 'valve' amps, ten of them. The best tube-tester in town wasn't for audio, it was a shipping company. CT is the only major port for thousands of miles, every ship including Russian checked in for maintenance — tanker, freighters, fishing fleets etc. Russians used tubes in all the electronics and those electronics are on all the time, in rough seas, being knocked around like Jake LaMotta in Raging Bull. Even tubes that were 60-70 years old, tested perfect.