lighting 'hum/tone"

[JBN]

I was shooting a corporate video yesterday with two talents in front of a green screen....simple set-up. I suddenly realized I was getting this high pitched "tone" in the headset from somewhere. Finally tracked it down to a small softbox I was using to add low fill to the front of the talent. Switching the softbox on and off pinpointed the softbox as the source of the hum/tone. I noticed that after I turned the softbox back on after a lunch break, it took a couple of minutes, but here came the hum/tone sound again after it warmed up. It's a Photoflex softbox (with the long tube bulb). I've used this softbox for 3 or 4 years and this is the first time I've had this audio issue with it. It's NOT the normal 60hz electrical hum. Any ideas why this is happening?
JB

[Barry_Green]

Bulb might be near the end of its life. Try a new bulb and see if it makes a difference.

[JBN]

Sort of what I was thinking. I'll give it a try. Thanks, Barry.

[kplo]

Sometimes an older bulb will have a "singing" filament; it's less common with modern halogen bulbs however.
In the "old" days, you could hear a 5k or 10k near the end of it's life all over the set...without a headset!
Is that bulb/tube a specialty item only distributed through Photoflex?
Ken

[JBN]

I don't know if it's a specialty item or not. I've been able to buy a couple of spares through a local dealer...and they are marked as Photoflex bulbs. I thought they would be extremely fragile whenI first saw them, but I've shot around the world traveling with them, and they hold up well. I finished the shoot today that I started on Wednesday...changed the bulb before we got started...and the weird hum dissappeared. So apparently it was dying anyway although I had no indication other than the noise. Thanks for the help.