Bogen PH-10

Hi Skip, I picked up a really clean bogen PH-10 amp. I changed the filter caps and it runs great, but it's not loud at all. It's got 2 6v6 1 6sl7 and 5y3 , 3 different rca inputs aux,radio,phono. I read some where that it's basiclly a power amp with phase inverter and no preamp.  What was this amp designed for originally and how would it be used.  If I want to use it for harp should I use some kind of preamp pedal or would it have to have the 6sl7 wired differently?  Or maybe just use it as is for listening to music.