MGA Mitsubishi Pre-amp DA P600 FUSE ..Help !

I just purchased this vintage pre-amp.
It works fine.
However I always check the fuses for correct values.
I cannot locate the fuse on this pre-amp.
I looked on the top and bottom inside the unit and also next to the off and on switch plunger.
Where is the fuse?  Is there a fuse ?
Could it be a resistor fuse?
If there is no fuse is that the way it was manufactured?
Please HELP !
Thank you