This style of the OVZ has confirmed to actually be the OVC. It was made alongside the OVS as a lower cost unit in the 80s. Then the OVC became a little bigger to accept 250W lamps and was renamed the OVZ and the OVS was enlarged to the OVX. The OVM seems to be the odd-guy-out with the OVD...
As far as i know the OVC was made in 35-150W HPS and 100-175 (or maybe even 250?) watts MV. The OVS came in 35-250W HPS and 100-400W MV (maybe it came in 400W HPS; i don't know...) The OVM was most likely made in 200-400W HPS and 400W MV, as that was the norm until the early 2000s to today.
Login
As far as i know the OVC was made in 35-150W HPS and 100-175 (or maybe even 250?) watts MV. The OVS came in 35-250W HPS and 100-400W MV (maybe it came in 400W HPS; i don't know...) The OVM was most likely made in 200-400W HPS and 400W MV, as that was the norm until the early 2000s to today.