After reading about some collectors attempting to run 700W H35 mercury vapor lamps on 1000W M47 probe start metal halide CWA ballasts by derating the series capacitor value from 24 microfarads down to 18.5 microfarads with relatively good results, I am interested in trying to find an appropriate capacitor value that is appropriate for running the rare 425W H40-17 mercury vapor lamps on 1000W M47 probe start metal halide CWA ballasts.

For reference, the 425W H40-17 mercury vapor lamps have an arc voltage drop of about 265V and an operating current of about 1.7A and is NOT interchangeable with 400W H33 mercury vapor lamps; the 700W H35 mercury vapor lamps have an arc voltage drop of 265V and an operating current of 2.8A; and lastly, the 1000W H36 mercury vapor lamps and 1000W M47 probe start metal halide lamps have an arc voltage drop of 265V and an operating current of 4.0A. So far, my initial guess is a capacitor value somewhere around 10 to 12 microfarads for the 425W H40-17 lamp if I am not mistaken. I am interested in answering this question because I am looking for easy ways to help collectors safely run 425W H40-17 mercury vapor lamps just in case they find any in the future, but they are extremely hard to find as they appear to have only been produced during the 1960s and would like them to make sure that those lamps would run properly.

The source that I used to find the electrical characteristics of the 425W H40-17 mercury vapor lamps can be found on the link below on page 15 of the following document:

https://www.scribd.com/document/394833080/Westinghouse-Mercury-Lamp-Brochure-1961