This was one of our longer-term projects. We took a 60-year-old, well regarded communications receiver, brought it back to its original specifications and then modified it to meet today's standards.

The HRO's were a series of receivers manufactured by the National Company that were first introduced in the 1930's. The HRO receivers were so well regarded during WWII that they were copied by the Japanese, Germans, Soviets and Australians (in that last instance, under license from the National Company). The HRO-60 was the last of the vacuum tubed HRO's and was manufactured from 1950 through 1967, a very long life for a communications receiver. Subsequent to the HRO-60, National produced two solid state HRO's, the technically advanced HRO-500 and the ultra rare HRO-600.

Our HRO-60 was in fairly good shape. Cosmetically, it didn't show its age. Most importantly, it was complete and for the most part, unmolested. We dated its manufacture through component date codes to around the fall of 1951, a fair early model.

Click on the topics to the left to follow the various stages of restoration and the modifications we did to this receiver.

Cleaning the chassis and case

Component testing and replacement

Adding a high voltage fuse

Adding a product detector

Adding a solid state 4H4C filament current regulator

Adding a mechanical filter

Select-o-Ject restoration

Coil box restoration

B+ switch "thump" elimination

The HRO-60 block diagrams

The HRO-60 schematics

The final restored chassis