I was most interested in reading the article "Restoring an Icon," in your July issue [page 64]. The mention of the "General Electric Thyratron tube-based dimming system" requires clarification.

This "system" was designed by E.D. Schneider of General Electric Schenectady along with Radio City Music Hall (RCMH) chief electrician Gene Braun. The dimmers were Ward Leonard Company's Hysterset saturable core reactors. The thyratron tubes available at that time (1930) were of low power, and were used to provide the control voltage that could be varied to increase or decrease the saturation of the reactance transformer. Unlike the later Izenour system, these thyratron tubes did not dim the load. It was, however, this principle that later gave George Izenour the concept to develop his system as higher-current thyratrons were produced.

The RCMH system had 328 dimmers ranging in size from 2kW to 16kW. Where lighting loads exceeded 16kW, multiple dimmers were used. There was a total of 1,556 lighting circuits. Stage lighting required 262 dimmers on 942 circuits, and 66 house light dimmers on 614 branch circuits. Other installations included the original Metropolitan Opera House and the Center Theatre, originally the RKO Roxy. The Met's system was by GE and the Center Theatre system was by Westinghouse. I must thank Lyman Brenneman for the above information.

In the early 1960s I was a sales engineer for Ward Leonard Electrics' dimmer division. We were contacted by Radio City's management company to investigate the possible replacement of the original 1932 system. I had the privilege of meeting Gene Braun. He loaned me a complete set of the original GE drawings which I carefully studied. I found to my surprise that the control technology of that original design had surpassed the design concepts we were promoting at that time.

After studying the RCMH design, I realized that with our control, potentiometers design, mastering and sub-mastering controls and duplicating the existing five-scene preset capability, we could no longer house the control console in the existing space in front of the orchestra pit. My plan was then to build a new control space at the rear of the auditorium. When I presented my initial proposal to Braun, I found out that the RCMH had never closed! Braun's concerns were not only for the lighting control system, but the rewiring of the entire facility. Insulation was falling off the wires on some of the stage floor pockets.

We had estimated a new lighting control system in the $1 million range. However, to rewire the entire building along with a new lighting control system would have required shutting down the theatre. But the economic losses incurred as well as the equipment costs could not be justified. The plans to replace the dimmer board were abandoned and I, now to my regret, returned those original GE drawings to Braun.

Over the years, Brenneman (who later headed up the GE division responsible for these systems) and I have talked about the uniqueness of the systems that had been developed by GE. Some years ago Brenneman (who remains active in the restoration of old theatres in the Cincinnati, OH, area) donated his set of drawings on the RCMH system to Bill Allison at Penn State's Theatre Department. However, in recent conversations with him, I learned he was told that those drawings could not be found. Perhaps, with this letter, a Penn State theatre major might undertake a search of the Theatre Collection there and find these wonderful drawings.

In "Catching the wave", it was noted that "In Europe, an ISO standard has now been set for mains harmonic distortion that from January 2001 will effectively eliminate the installation of phase control dimming as we know it." Dimming authority Adam Bennette reports this is not the case, and corrects ISO to IEC.

Video design for the Cure ("Bloodflowers in bloom," September LD) was by Robert Smith, Richard Turner, Abigail Rosen Holmes, and Clarke Anderson; Anderson was the show's video operator.