SSR for speaker protection?

The transistor must be capable to resist to a much higher voltage. The load is inductive and in case o a failure in the amplifier the current will refuse to stop when the SSR will open. The protection for transistors should be updated accordingly to the transistor voltage and amplifier power.
 
Yes, that’s a good one. Look for low RDson and make sure it can handle the voltage of interest. 100v in this case.

I use 150v MOSFETs on mine so they can handle 300w amps - similar to Infineon BSC0402, for example.
Thank you all.
Xrk,I see your options,hard to hand soldering, i see some other through hole high voltage and low RDon options in mouser too,0 stosk many of them.
I just look for available and not very expensive MOSFET.
I know...not an easy job.
 
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Solder paste and hot plate is very easy and greatly opens up your options to low cost high performance parts.

https://www.sparkfun.com/tutorials/59

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Here is a video of my hot plate:
 
The transistor must be capable to resist to a much higher voltage. The load is inductive and in case o a failure in the amplifier the current will refuse to stop when the SSR will open. The protection for transistors should be updated accordingly to the transistor voltage and amplifier power.
Going a little higher (like 150 or 200 volts) is of little help by itself. The voltage will try to spike many times the supply voltage when the relay “opens”. Adding a TVS, snubber, or another set of freewheeling diodes on the load side is what is required - and that will let you use the lower-Rds(on) 100 volt mosfets. If you used 600 volt mosfets it might still not be enough without other protection mechanisms - and will have much higher ON resistance to deal with.