TIL why old theater dimmers hum so loud

Was helping a buddy with a lighting upgrade at a 1920s theater downtown last month. We pulled the cover off an old resistance dimmer board and I finally got why those things sound like angry bees. The carbon discs were worn uneven and arcing every time the current passed through. Manager told us it had been humming for 15 years and nobody ever bothered to look. We swapped in a modern solid state rack and the silence was weird at first. Anybody else run into old dimmer setups that are just begging to be replaced?

2 comments

2 Comments

maryadams25d ago

That humming sound is honestly terrifying once you know what's causing it... all that heat and arcing just waiting to turn into a real fire. Fifteen years is wild, like nobody wanted to deal with it until something actually broke. We had a similar setup in an old community center near me and the dimmers would literally glow orange if you pushed them past 80%. The silence after swapping to digital is definitely eerie at first, but way better than the alternative.

kevin_sullivan25d ago

Totally agree, @maryadams - that orange glow thing is nightmare fuel. We had a dimmer in my old theater that would buzz louder the more you dimmed it, like it was arguing with you about it. Swapping to digital felt wrong for like a week, but now I can't imagine going back to that constant hum.