jazzyvee , perhaps my friend . On your Twin ___, if you hear a constant low frequency tone then for sure .50HZ or 60HZ depending on your AC . Sometimes you can even hear harmonics of that low frequency.
What Keith writes of recondition the capacitors by slowly applying voltage is done with a Autotransformer . Variac is a brand of such a device. I have a few of them. In theory if you apply a greatly reduced AC potential (voltage) say about 60 volts AC for 12 hours or so and then bring it up to 80 and in another hour or so slowly to full rating of the equipment requirement and then just leave it powered on . The capacitors MIGHT reform . I do this often with old pro audio gear that someone has stored for many years . It would be part of the procedure to do a physical inspection of the individual capacitors for leakage. In old AMPEX tape transports and electronics this is a common . The Ampex machines were very robust but you can not expect all the electrical parts of a 1950's /60's &70's machine to not require service as is the case in all equipment . Not all capacitors are of a type that can reform and just need to be replaced
How I have approached some issues is ; In the case of your blue box you can just plug it in with your bass NOT connected and the next day check the voltages) check with a volt meter. I have also checked for ripple current with an Oscilloscope . Here is the PIN OUT ;
Voltage; +/- 15V DC to aprox 22V DC ,but check With Mica
1 ground
2 neck pickup
3 bridge pickup
4 + volts
5 - volts
Even if the voltages are steady and correct the filtering capacity of the capacitors could be compromised and as Keith writes replace them.
Best bet in my opinion would be to see if Alembic will recondition and upgrade your power supply if you have any doubts.
