Can I Use This?

Can I Use This Power Amp With A Guitar Preamp

Do you want to run an amp dedicated for hi-fi as a guitar amp or you want to use guitar preamp for hi-fi?
I guess first. If I'm correct, than yes, 90 Watts power amp is probably suitable for guitar unless you want to overdrive it. Than you would need more output devices.

I Need An 80 volt 1.5 ampere Power Supplie, Is It Possible To Do It?
No, you need more current if you want to run 8ohm speaker.

Do I Have To Put 100 volt rated capacitors?
Yes. Or even more.
regards
 
Yes, you can produce a 90 watts RMS amplifier using 2N3055 transistors

Also you can construct a 70 volts supply, using the external wires of a conventional 35 plus 35 symetrical supply.

Of course, a 90 volts supply can be constructed using a common 45 plus 45 volts simetrical supply, changing rectifier connections.

Yes, you will need 100 Volts rated capacitor.

Buen trabajo hermano, una tequilla pra nosotros.

saúde.

Good work brother, one drink for us

Cheers,

Carlos