Electro Harmonix 12AY7 Tube

The working one is great, gave my cub12 a whole new life, now when cranked gives this sweet creamy rich crunch, love it.
The other one I tried to put it in my champ clone, but the thing didn't start at all, no light, no sound, nothing. What a bum.

Used to replace V1 12ax7 in a Vox AC4 to increase clean headroom/reduce gain levels. I still get plenty of growl, but can keep the signal cleaner to higher volume levels where the 12ax7 went into overdrive rather too early.
A rounder, cleaner sound still with bite on initial pick attack is what I was after, and that's what I got. The amp now blooms into full chords with lots of lovely chime, but still barks with authority when the gain is cranked.
If you find the gain a bit fierce, try subbing a 12ay7 into your V1.