Restoration of National HRO-60Author: Edgardo Castro Bruse
San Salvador October 2022
I obtained this radio back in 2003 from my friend José Antonio Guevara, YS1JW.
Initially I repaired this radio in 2003, and at a later time, I was able to get two other plug in coil sets. Thus I was able to cover from 25 to 35 Mc. with Box AB. From 1.7 to 4 Mc. With Box D and from 50 to 54 Mc. With Box AD. It becomes evident that a major section of the short waves was left out. Please see pictures.
Description of HR-60
This radio is able to tune from 50 Kc. To 35 Mc. And from 50 to 54 Mc. By means of 13 plug in coil sets or plug in coil boxes.
Above 7 Mc it uses double conversion. The first IF is 1990 Kc. And the second IF is 455 Kc. It has a crystal filter with variable selectivity in 6 steps. It comes with 2 steps of RF amplification and a push pull of 6V6 s in the audio amplifier. It receives AM, CW and SSB in the CW mode. Please see here
2022 Mayor Repairs Steps
For almost 20 years I had postponed the repair of the contacts (inside the radio) that connects the coils in the plug in boxes to the circuitry of the radio. Each band has its own plug in box. These copper strip contacts were much deteriorated, but the radio operated miracously well. Please see pictures.
A - Reaching the Band Change Contacts.
There are 4 porcelain boards. Each one carries 5 copper contact strips. These boards are bolted under the chassis and become visible and functional trough 4 openings in the chassis. To take off these boards, in order to repair the copper contacts, one must first, remove the band indicator cylinder, then the huge variable condenser and finally the metal frame under this condenser. Note: carefully mark the wires of this condenser before disconnecting them! Please see pictures.
B - Repair of the Copper Strips.
This project was possible because, finally I was able to find and buy in eBay a porcelain board with excellent copper strips.
I removed the porcelain boards one at a time, and carefully marked each wire.
C - The Variable Condenser.
D - The Short Wave Converter.
To help the reader visualize how the variable IF works, I have prepared a table of data considering three different crystal frequencies and box AB.
You can easily see that, with Box AB, a 17.00 Mc crystal would provide a tuning range from 8 to 18 Mc. Please note: the IF frequency is the HRO reading minus the crystal frequency. My friend Dr. Andres Goens YS1AG had a 17.23055 Mc. crystal which was close enough and my tuning range was slighted changed from 7.77 to 17.77 Mc. Consequently the RF stage of the converter must tune from 7 to 18 Mc. Please see table of data.
E - Conclusion.