PA question

[luke12345]

Hi there,

I've been asked to look at a really old PA system at a school that consists of 7 horn speakers, of which only 1 is working.
The other 6 are on the roof all red from 1 cable straight from the amplifier.

I've never really worked with PA systems before and was wondering how do I go about fault finding it? Is there a way to check if a signal is coming to the roof? are the polarity sensitive?

All the 6 horns on the roof say 'Driver Unit 150w 16 ohm' and the amplifier says 4.8 ohm output? is this correct?

Sorry for sounding so vague

Any help would be great

 

[DPG]

Don't think there's any 100V line stuff here - seems like low impedance stuff from the OP, although could be wrong. If it is then the fault finding, as stated before, is simple continuity of wiring and resistance of speaker testing. As long as you can work out series/parallel impedances then job's a good 'un.
Ensure the total impedance of the speaker network is something around the recommended impedance for the amplifier and all should be OK.

PS, that's a nice big valve amp at 75W Lucien - KT88 tubes? Daz

 

[luke12345]

Sorry for being a bit brief on my initial post, it was all I could remember.

The system was just a crazy rig up with twist connections everywhere!
After ripping it to bits and testing as suggested, it turned out to be the input aux cable that was faulty! Doh!

I didn't check it because the amp was displaying an input from the aux when there was nothing. (if that makes sense?) Is this a sign the amp is on its way out?

Cheers again for the help!

 

[Lucien Nunes]

the amp was displaying an input from the aux when there was nothing. (if that makes sense?)

Sorry, it doesn't! But you've fixed it anyway which is good.

Daz, not KT88s but 807s, one of my favourite all-purpose output bottles along with their big brother the 805.