Fair enough, but even the lamp and photoresistor kind has an oscillator behind it. Look at the typical Fender, it has the triode with the three feedback caps, the the output of that drives a second triode to work the lamp. The oscillator determines the speed, the lamp is just a way to get that oscillation over to the signal path. When the trouble is too fast or too slow, it won't be the lamp and photocell's fault, it will be the oscillator.
I'm not picking on you, just pointing out that circuits are circuits, and many of them work about the same regardless of the technology under them. And troubleshooting is troubleshooting, a systematic approach to solving problems. if you know anything about fixing tube circuits, you probably know quite a bit about troubleshooting that applies to transistors as well.