Audio crossover component with reference designator of REX.

[paul8f]

Hi,

I'm returning to the Electronics world after a bit of an absence, so I'm a bit rusty to say the least...

Came across two boards recently that both had components marked as 'REX' on the PCB silkscreen. The 1st board was a microphone pre-amplifier for a vocoder, and the 2nd board was a hi-fi speaker crossover device. At first, google was telling me that the letters were an acronym for 'Range EXtender', but that seems kinda wrong in this case. So, my question is what do the letters REX stand for, or were abbreviated from?



(After doing a little bit of digging, I discovered that REX components can be one of 2 types. The first being a resettable fuse (multifuse/polyfuse/polyswitch), and the second being a small lamp (soft protector or tweeter limiter) that looks like a cartridge fuse . I think the idea is that they protect the delicate tweeters from receiving too much power by absorbing unwanted transients. Could the R in REX stand for resettable??)



Anyway, if anybody knows where the name REX comes from, I'd be interested to know.
Paul

[macboy]

An incandescent lamp works much like a polyfuse in that both have a PTC or positive temperature coefficient.
In this case, they won't absorb transients, but much to the contrary, will allow brief transients to pass through. Instead, continuous high (high for a tweeter) power will cause the device to heat up and increase its resistance, which effectively reduces the power allowed through to the tweeter.  Brief or occasional transients won't result in enough heating to trigger this effect. Likewise the tweeter voice coil can handle brief or occasional higher power transients but would overheat with continuous high input.

[paul8f]

PTC or positive temperature coefficient.

Yeah, it's all about the temperature coefficient.

Good point as well about it being the 'continuous high power' that's to be avoided.

Still no idea what the letters R.E.X. stand for, but at least now I understand how the component works, and can recognise it in the future!