At this point, you would need to track down noise problems with the aid of an oscilloscope or at least a signal tracer to identify where the noise arises. That's difficult and very time consuming for the inexperienced, with the usual end result of giving up and blanket replacing of all caps in the signal path and also the supply decoupling caps in both power amplifier and preamp (tone control section). That's about every small electrolytic cap in sight and there are lots in this old beast.
You could separate the power and preamp sections at connection points 1 and 2 on the schematic and check that all the noise arises in the preamp but symptoms are that you need to recap the preamps completely. You don't need to ask about what is the most wonderful brand/grade of cap. to use here or there, as you will soon get tired of it when there are so many that simply need replacement. Panasonic FC will do fine just about anywhere and remember that you don't need to use the low rated voltages like 6V when modern caps are quite small enough so if you use 100uF 25V, rather than 100uF 6V, it's probably a better choice, provided it fits the available space. You can err by up to +100% of the specified value in most applications without problems so don't be too fussy about available part values which have wide tolerances anyway.
I can't tell if the caps are radial or axial leads types but the available axial lead types are limited in UK supplier ranges at least, so you may have look further afield.
Generally, with amplifiers before about 1980, some low level audible hiss and noise that increases with volume, is inherent to the simple designs (its usually obvious in the specifications too) and you do have to learn to live with it.
You could separate the power and preamp sections at connection points 1 and 2 on the schematic and check that all the noise arises in the preamp but symptoms are that you need to recap the preamps completely. You don't need to ask about what is the most wonderful brand/grade of cap. to use here or there, as you will soon get tired of it when there are so many that simply need replacement. Panasonic FC will do fine just about anywhere and remember that you don't need to use the low rated voltages like 6V when modern caps are quite small enough so if you use 100uF 25V, rather than 100uF 6V, it's probably a better choice, provided it fits the available space. You can err by up to +100% of the specified value in most applications without problems so don't be too fussy about available part values which have wide tolerances anyway.
I can't tell if the caps are radial or axial leads types but the available axial lead types are limited in UK supplier ranges at least, so you may have look further afield.
Generally, with amplifiers before about 1980, some low level audible hiss and noise that increases with volume, is inherent to the simple designs (its usually obvious in the specifications too) and you do have to learn to live with it.