The SP is one of the four older style Golmar speech amplifiers still available.
Golmar SP speech amplifier
The Golmar SP speech amplifier is one of the four older style Golmar speech amplifiers still available. 8v dc & 12v ac
It has two pots. for adjusting the speech volume at both the panel and handset.
The connections on the unit are as shown in the close up image.
note: the SPTF speech amplifier looks very similar but they have different terminal connections. Check closely your existing unit.
70mm x 80mmx 25mm