A DIY Power Supply Replacement
     

Fig. 1: The Mean Well replacement power supply for a BE FM1C1. Fig. 2: Drilling holes in the side of the transmitter to mount the new supply.

Apex Broadcasting’s Chief Engineer Bruce Roberts came up with a handy solution after he lost the power supply to his BE FM1C, a 1 kW FM solid-state transmitter.

He writes that BE makes a conversion kit for the FM500/FM1C but its cost was outside of his budget, so he ended up removing the transmitter from service, sticking the unit in a corner and using something else.

From time to time Bruce did an online search for a 48V 50 amp supply but couldn’t find a suitable candidate. Finally, he discovered the right substitute supply, at TRC Electronics, for $438.60. (I posted the link at radioworld.com/links.)

The supply is a Mean Well Enterprises model RSP-2400-48, seen in Fig. 1, and the installation procedure was pretty simple. The hardest part was removing the old supply. After removal, Bruce drilled the side of the transmitter to mount the new supply, as seen in Fig. 2. A template for mounting screws can be found on the supply PDF from AllDataSheets.com (again see radioworld.com/links).

The other issue was finding a plug to connect to the new supply in order to “mute” the voltage when transmitter is off. The old supply had a small white wire that supplied +12V to mute the power supply when the power is turned off on the front panel.

To accomplish the mute function on the new supply, plug CN1 pin 1 gets grounded, and the white wire connects to pin 2. You’ll find these pins identified on the supply PDF described above.

Fig. 3: The new supply is mounted in the transmitter. Fig. 4: Up and running on the new supply.

Fig. 3 shows the supply mounted and wired up. Note the aforementioned “white wire” in the upper corner, which has been extended to reach CN1.

Fig. 4 was taken after the transmitter was returned to service.

* * *

Hall Communications Vice President of Engineering Edd Monskie commented about our description of Alan Peterson’s antique radio that played holiday carols in the station lobby.

When Edd was in college at Ball State University in Muncie, Ind., he and some friends took an old antique Zenith cabinet radio, got it working, tubes and all, and placed it in the lobby of the college station, WBST(FM). They then took an old FM receiver and, using the proper coupling, connected the FM receiver to the shortwave input of the radio band selector switch.

They had the air signal of the FM station playing in the lobby, through that beautiful, 1930s walnut cabinet. It sounded fantastic.

Edd adds that as long as he worked there, no one commented on the fact that FM had not even existed when the AM/shortwave radio was manufactured.

Thanks, Edd, for a neat memory.

* * *

Cumulus Youngstown’s Wes Boyd found a YouTube video that anyone dealing with EAS and weather-related radio will appreciate. It’s the voice of NOAA Weather Radio singing “Deck the Halls.” Gotta love the fa-la-la!

Find it at radioworld.com/links.

Contribute to Workbench. You’ll help your fellow engineers and qualify for SBE recertification credit. Send Workbench tips to johnpbisset@gmail.com. Fax to (603) 472-4944.

Author John Bisset has spent 43 years in the broadcasting industry and is still learning. He is SBE Certified, and is a past recipient of the SBE’s Educator of the Year Award.


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