Soundhaspriority wrote:

"Eeyore" wrote in message

This is a well established technique for preventing voice coils burning
out under conditions of 'overdrive'.

There is a stage monitor I'm having problems with that uses this method.

The HF sounds very distorted and almost cuts in and out.

I looked closely inside and found some damaged push-on terminals. Ah, I
thought, probably a poor contact causing the probelm, replaced them,
checked driver DC resistances etc, reassembled thinking I'd probably
fixed it.

But no, the low level HF and distortion continued.

I'd checked the DC resistance of the protection bulb but later it
occurred to me that it might have 'very nearly' burnt out and have a
weak spot that wouldn't show up on a DVM but passing signal would heat
it and cause this trouble. I'll be able to find out soon enough but I
wondered if anyone else had ever encountered this ?

I think it's unlikely, because any fracture causes a local hotspot, which
rapidly leads to failure. I'd look at the socket instead!

I will double check that. Thanks for the tip.


We've probably
all seen strange tin-lead phenomena on lightbulb button contacts. The
constant thermal cycling, the pressure, the dissimilar metals...

Interesting point.

Graham