It sounds to me as though you have a Lansing 285, the large format compression driver with the radial slit phasing plug. Is this the case?

The ratings stamped into the metal badge would be for DC voltage operation of the field coil. 220VDC was the most common field supply voltage for these drivers, being used routinely in the Lansing Shearer Horn systems. 25 watts dissipation in the field coil is also correct for these drivers. Field coils were also wound for other supply voltages, so you should be sure before applying voltage.

I have a couple of 285 drivers in my collection rated to run on 220VDC. Their field resistance measures about 2,500 ohms.

Calculating the correct supply voltage when the DC resistance and dissipation is known is an Ohm's Law calculation. Please contact me here or at stfrsc@juno.com if you would like assistance with this.

• Lansing 285

Good to see you here. Last I heard, you were making your own compression drivers. How did that work out? What are your latest projects?

Wayne

When these drivers were used in the theatre systems, a dedicated field supply was part of the equipment. It powered all the field coils in the system, which could be up to six compression drivers and woofers in total. The circuit was simple; power transformer, rectifier tube(s), choke and filter capacitor. The old field supplies usually still work fine when they can be found, but are quite scarce these days.

Generally I use a bench type variable voltage DC supply, like the ones made by Lambda, Kepco and others. One needs to be found with the correct voltage range and adequate current rating. If you would like to build an original style field supply, let me know and I'll send you a scans of the schematic diagram.

Rich and I are still working steadily on our driver designs, and hope to be able to offer them for sale within a few months. We are about finished with the design of our DS-1428 mid / high frequency compression driver, which is based on the RCA MI-1428B of the late 1930s. We are also developing the DS-1448 bass compression driver, similar in design but scaled up in size. Our horn designs have been evolving as well. Stay tuned!