Posted by Lance on February 23, 2003 at 17:18:11

In Reply to: Re: MV Rectifiers - OK-OK-OK! posted by Dave-A on February 23, 2003 at 16:33:50:

What you saw was not a flash-over. A flash-over occurs with HV applied and is essentially an internal short. What you saw was an effect caused by insufficiently developed gas plasma caused by not allowing the tube to heat up long enough. Formation of the gas plasma is important as it protects the filament from back bombardment from high-velocity positive ions. This back bombardment will eventually destroy the oxide coating on the filament. These tubes are also sensitive to over and under filament voltage. In commercial use most are operated with some type of a constant-volatge transformer that incorporates both over and under voltage relays which will open the HV supply primary if an out of range filament voltage is detected.

Undoubtedly, running MVR at lower ratings will help but all the issues with filament voltage,warmup and temperature range are still present.

One last thing. MV rectifiers can have breakdown efects in the MV plasma if subjected to strong magnetic fields. They should be located a reasonable distance from chokes, power tansformers and OPT's. If subjected continually to these fields tube life will be shortened.

Check the particular tube specs. for the recommended warm-up time.