Need help finding or crossing these components

[NBARSIX]

Working on an old (1965) speed controller and need to replace a couple of parts. Tried the old google search for the part no's I have, but couldn't match. Its made by Minarik Ele. Co. (still in buisness). The 1st is a M668 (Minarik P#) Silicon Diodes, 750ma, 600piv. I think thats a bridge recitifier (has 4 legs). The other is a M608 (Minarik P#) 8J1 Selenium Rectifier. A transistor? This part is a disk approx. 1/2 an in. pressed into a plate that is hot, with 2 terminals. I will attempt to enclose pictures. PS, whats a piv value? Thanks. Can't seem to attach my pictures. Comes back with "server error". Can email to anyone interested. Thanks

 

[shrtrnd]

If the company is still in business, ask them.
You're not going to find anybody else who can cross those part numbers.

 

[duke37]

PIV = Peak Inverse Volts
This is the maximum volts which the diode can withstand in the reverse direction.
A 1N4007 can pass 1A and has a PIV of 1000V. You would need four to make a bridge.

Selenium rectifiers were often used for low voltages. They degrade with time so an alternative is better.

 

[TorontoBob]

Working on an old (1965) speed controller and need to replace a couple of parts. This part is a disk approx. 1/2 an in. pressed into a plate that is hot, with 2 terminals. I will attempt to enclose pictures.

This part sounds like an SCR or Triac.

You didn't say what type of speed controller? Is this for a low voltage DC motoro, or for a line voltage, DC, or AC motor controller?