Reviving the HRO-60

First a little history for those who may not know what a HRO-60 is.  The HRO-60 is an amateur radio receiver or communications receiver.  It receives all the amateur radio bands and the full spectrum of the shortwave bands that the amateur bands are part of. The HRO is not a new receiver. The version that I have was made from 1952-1962 by the National Radio Company. National was located in Malden, Massachusetts until 1957 at which time it moved to Melrose, Massachusetts. The National HRO-60 was and is still considered as being one of the best shortwave receivers ever made. My HRO-60 is at least 56  years old because it was manufactured in the Malden factory. Back then it went through a number of price changes with a beginning low of $483.00 and ending up at $745.00 . That was a lot of money back in the 1950’s and ’60’s.

My HRO-60 was given to me some 20 years ago by a friend who had no interest in it. The only catch was that I had to remove it from the third floor of his house. The radio weighs over 85 pounds. It’s real easy to hurt your back with this one. They sometimes refer to radios of this era as boatanchors. When I have need to move it I usually wait for my son Alex to come home and give me a hand. My boatanchor has been working well for many years. Then a couple of years ago it began to have a problem turning on. After turning the radio on nothing would happen and then several minutes later it would come alive. I pretty much ignored this .. not a good move.

Last month the radio finally died. It blew the fuse while I was attaching an antenna to the back. I thought I had shorted something so I took the covers off and removed the few loose washers I found floating around inside. Then I put in a new fuse and tried again. The fuse blew again (expensive fuses too!). Several fuses later I decided to purchase a new filter capacitor (the really big one). These sometimes short out and destroy an otherwise good radio. I was able to find a new capacitor on e-Bay. It came all the way from China in less than two weeks. It was a brand new dual capacitor rated at 50 microfarads and 50 microfarads at 500 volts. That was close enough to the 40 mfd x 40 mfd at 475 volts unit that I was replacing. Bigger numbers, within reason, are better.

The new 2-section filter capacitor is the big black one. The disonnected failing capacitor ( C118) is the red one.

I replaced the filter capacitor and put in a new fuse and promptly blew the new fuse. Now I had to get serious. I did a search on the Internet to see what else might be the problem and found out that there was another capacitor attached to the power supply output (C118 – some hobbyist actually remembered the designation!) that often shorted, blew the fuse, and destroyed the power supply (real expensive to replace if you can even find one). The accepted modification was to just remove the capacitor and prevent a meltdown. This was bad news. The horses were already out of the barn as they say. I located the C118 (I have a PDF of the original manual and schematic) and noticed that mine seemed to be leaking some white stuff out one end. More bad news. So as a last resort I unsoldered C118 from the circuit and brought the radio to life slowly with a variac and a series-attached light bulb to absorb any excess amperage. The radio lit up, barely. Even at 100% power I had no reception. Sometimes when you power a radio with a variac the unit never gets quite enough juice to come alive. There is only one option left. Plug the radio in to the wall directly, turn it on, and hope for the best. That’s what I did. Within seconds the old HRO-60 was once again pumping out Morse code, international broadcasters, and religious stations. It’s ALIVE!

At this point I really should research the other modifications necessary to preserve this electronic relic for another 50+ years. I may .. but then I am the lazy type. I’m just happy that this was a successful Sunday.

(Watch my HRO-60 play on You Tube – it’s the number one result on Google when you search HRO-60.)

Update: Upon shutting down for a couple hours and then turning the radio back on, it blew the fuse again. It looks like I have more work to do. I will upgrade the fuse (currently using 1.5 amp – should be 2 amp), but somehow I suspect there is something else going on. Any suggestions are welcome.

Update #2: Today I replaced capacitors C-70 (electrolytic, 25 mfd. 50 vdc) and C-79 (electrolytic, 25 mfd. 50 vdc) at the suggestion of Bill, AK5X (please check out his excellent Flickr site) . In both cases I used recovered (pull) 47 mfd 50 vdc modern electrolytics. I first checked each one on my Solar capacitor checker to see if they were up to specifications. I left the 1.5 amp fuse in place. I tied the capacitors into the circuit temporairly with alligator clip leads (parallel to the old cap’s.). Upon powering up with a variac and series light bulb unit, the radio turned on (panel lights lit up) but never produced any audio. After 30 minutes or so I disconnected the variac and series light bulb and turned the HRO-60 on while connected directly to the AC with no protection other than the 1.5 amp fuse (remember, 2 amps is the schematic recommendation). Panel lights came on within 10 seconds and loud audio was present within 20 seconds. Success! Even after a two day power down, the unit powered up nicely with the caps in place. Today (1/24/13) I soldered in the new caps and removed the old. The radio now powers up quickly (panel lights in 10 seconds, audio in 25) and produces a signal that is louder and clearer than my Icom IC-737 transceiver. I did not hide the new caps in the old tubes (considered it) but I did have to graft spare leads (sourced from some ceramic caps) onto the electrolytic pulls since the modern capacitors had short leads. Today has been a good day.

Caps

Original capacitor case at top, removed tube in middle. I replaced with the new capacitor (bottom) after grafting on lead extensions. Polarization of old and new are matched.

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