Details and two more questions:

Xenon lamp went out on first preview tonight. Almost the last thing I checked was the fuses on the 3-phase disconnect box. Fuses okay, but after turning box off and on, the lamp struck.

Whatever this problem was, it blew a diode - we had the characteristic dark flicker as soon as we went on screen. Show ran successfully. Only two patrons had enough sense to complain. We may not be able to get replacement diodes for 24 hours. I may be under pressure to run three shows before then.

This equipment is old:
Christie rectifier Model No. CC20U
Xetron lamphouse Model 2000 Type XH11 retrofitted with a 1600 watt kit

Second question: When I flipped the switch to manual to strike the bulb I heard a shorting noise from the lamphouse. Like a loud hum. It sounded as though it came from the front of the lamphouse. Later, when I was able to strike the bulb, the noise was not there. (This is not a console unit - the power supply is in another room.) Any ideas on the source of the noise?

The only problem in continuing to run it is that if the diode failed as a short you could damage the winding that feeds the diode. Sometimes the fuse/breaker will not blow and the winding will do a slow cook till its toast. You'll smell it for sure. If the diode opened as most diode failures in Christie's do then you will not damage the rectifier. Its not great for the lamp as the resultant DC voltage has lots of ripple on it. When you replace the diodes look at the center part where the stem comes through. If that center is glass the other diodes should be ok. If that center is a green epoxy then replace all your diodes(you'll probably find the stem is loose as the junction has failed). The epoxy type are all prone to thermal failure. The remainder of them will eventually fail. The glass sealed type are the best to use. These type are more capable of coping with the thermal stresses of going form hot to cold over a several year time period. Interestingly Christie still supplies the epoxy filled type if you order the diodes from them.

When installing the new diodes coat the base of them with white silicon grease for best heat transfer. Also a small fan(4" muffin type) should be placed under the heatsink assy to improve air flow through the rectifier unit. All new Christie rectifiers(at least on consoles) have this fan. Old Christie's did not. Doing this greatly extends the life of the diodes.

The lamphouse being single phase and the rectifier 3 phase is a US standard. Only european lamphouses are typically 3 phase.
Mark@GTS

Thanks for the information!!

I was able to get it repaired before showtime, much to my relief.