Peavey Power Amps

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I'm intrigued by these big rack mounted amplifiers with the handles 

I'm seeing various models like the M-2600, IPS-800, CS-400....

Stupid question like always...what do/did people use these amps for ? I'm guessing it was to play loud music at an event like a wedding 💍💒 reception or keg party  or maybe it was part of a band's equipment playing live ?

Anyhow another stupid question when I see rows of output transistors I wonder aside from being shorted which I guess would be very obvious and a big problem...do they fail in other ways?

For example if they have one channel with eight big outputs could it be the amp is slightly down on power because one or more outputs is not contributing? Like when you have a vehicle down one cylinder and you can feel it or hear it.

[Loudthud]

Every Power transistor has limits on how much Voltage it can withstand, how much current it can conduct and how much power (Voltage x Current) it can dissipate. The design of a power amplifier must take these limits into consideration if it is to operate without failure.

High power amplifiers use a number of transistors in parallel because of these limitations. If one of these transistors were to fail, the chances the amplifier will keep operating are fairly slim.

Bipolar transistors suffer from an additional limitation called "Second Breakdown". A transistor may be rated at 150 Watts, but at higher Voltages, they cannot dissipate that amount of power. They will fail. To get around this limitation, high power amplifiers use many transistors in parallel.

To see more about Second Breakdown, see this thread:
https://www.ssguitar.com/index.php?topic=4897.msg38561#msg38561

[g1]

Also, power transistors are more likely to short than go open.  A shorted power transistor will shut down the amp one way or another.  And in the cases where one opens instead of shorts (or if it's emitter resistor opens), than the others in parallel with it have to do more work, and usually this leads to more failures.

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what do/did people use these amps for ? I'm guessing it was to play loud music at an event like a wedding 💍💒 reception or keg party  or maybe it was part of a band's equipment playing live ?

PA systems used to be a lot of non-powered speakers and racks of these big power amps.
The first powered speakers I'm aware of were powered subwoofers.  Because they still used regular power transformers they were very heavy.
Once SMPS (switch mode power supplies) became more common, more and more speaker cabs became powered.  SMPS replace regular power transformers with a very lightweight electronic circuit.
Most speaker cabs now are powered, but even stand-alone power amps now use SMPS, so they are also very light on a pounds-per-watt basis.
The downside of SMPS is longevity as they use a lot of capacitors that do not like heat and have a finite lifespan.
If you don't need mobility, the old power amps you can find are a pretty good bargain, especially if you find speaker cabs that are being junked because their amps are blown.