RAN Technology

Replacing C-frame fans

Technical 0 Comments 04/23/2021 

Boatanchor parts from the home improvement store

Posted By: Robert Nickels (ranickels)


It's not often that you can buy a replacement part for a vintage transmitter or amplifier off the shelf at the home improvement store, but this is one example.   And since it's not a perfect drop-in replacement, here's now I adapted a new Broan-Nutone BP-27 bathroom-kitchen exhaust replacement fan to fit into a Johnson Desk Kilowatt.

These small shaded-pole "C frame" motors have been produced for 70+ years and continue to be manufactured by a number of companies because they do the job and are inexpensive.   While it's not surprising they don't last 50 or 60 years, with occasional oiling they're pretty reliable in operation.

Over the years, the design has evolved to improve producibility and rather than try to find an exact replacement I adapted the BP-27 50 cfm fan motor that was in stock at Menards.     There are a few differences, including a larger diameter shaft which requires drilling-out the fan blade with an 11/64" or #17 drill.   The bigger problem is shown in the comparison below: