When the amp was recapped, were _all_ the capacitors replaced
including the twist prong cans and axial electrolytics? An open
electrolytic in the cathode circuit of the preamp section will cause
much lower volume.

If you pull out the automatic volume control tube does the sound get
much louder?

Many times the resistors in these old amplifiers will drift way off
value and need to be replaced. Have all the resistors been checked for
value?