New power supply for 1936 HRO Sr. radio



This power supply was designed and built to power a National HRO Sr. radio at the American Museum of Radio and Electricity in Bellingham, WA.  The radio was originally designed to operate with an external "doghouse" power supply with an output of 240 vdc @ 70ma and a filament supply of 6.3 vac at 3.1 amperes.


This project resulted in a supply with a measured output voltage of 248 volts at 75ma and an adequate filament supply.


Special thanks to Jonathan Winter, the museum's curator, and John Eisenberg (K6YP) for their help in designing and testing this power supply.


Transformer: Hammond P-T273CZ
Filter choke: Hammond P-T159T
Filter capacitor:  Mallory C-EC30X3-525



Most of the components were sourced through Antique Electronic Supply, Tempe, AZ



Laying out the holes and drilling, punching and filing took most of the time on this project.







I used a small CPU heat sink to dissipate the power from the bleed-down resistor.  About 3 watts.  Probably overkill.