GenRad 1960s sound level meters restoration

[jonpaul]

Bonjour a tous:
Our  Museum has received four General Radio Sound Level meters, 1565-A circa 1960s..1970s.

One  ceramic mic element is missing. 3  original GenRad leather cases. one  1562-A calibrator. No battery damages!

All sort of work. One  broken meter face,

Adjusting  CAL pot.   with  sound level calibrator all read low   10..20 db

I   suspect, aged  ceramic mic elements

Perhaps  transistors,   caps, resistors, pot, switches ?

Any  ex GenRad, or noise reduction or acoustic experts  out there?

Any experience or advise is appreciated.
 
Many thanks


Jon

[GLouie]

I am not an expert! Is the calibrator known to be good? If electronic, it could easily be bad by now; if pistonphone, less likely.

I see the manual with schematic is on the IET site.