Junk or Joy? : Heathkit GR-78 Shortwave / Amateur

Figure 1:  The venerable? Heathkit GR-78 receiver, as it was found in flea market.  

What ham can resist the allure of a piece of vintage gear, sans cover, knob, and a part or three, looking ever like the cartoon character with sprigs of pointy wire hair protruding from here and there, connecting to nothing?  When we go to ham swap ‘n shops, we brace ourselves ahead of time, lest we not load our trunks with the contents of theirs.  We have time in such cases to revisit the vision of our junk corners at home, and the XYL’s displeasure of same.

But …

When you are innocently walking through a regular old flea market, mostly the sort of place that harbors rock band tee-shirts from the seventies, the printing of which is almost unfaded enough to read, and which are accompanied by matching scratchy vinyl records, then your inner ham’s expectations are low. You are not pre-prepared to resist boat the anchor sirens.  That prize example of granny’s old tupperware (sans lid), appears, but then – just to the left of the tupperware, is what?!  Could it be?  The dial says ham, but closer inspection says shortwave.  OMG, what a find!  For the moment, the boat-anchor addiction takes full control, via the subconsciousness’es prodding.  At that point, there’s no hope.  It’s so much better than the tupperware.

Me: “Whadda ya take for the radio?”

Flea market merchant:   “Been asking twenty five, but for you – twenty bucks.”

Me:  “Let’s see what I have in my wallet.  Hmmm, fifteen dollars.  Here you go!”  (I hand him the cash, and he takes it, but passes it back and forth from one hand to the other.  The corner of his mouth wrinkles a little).  My flea market trick (put the money in their hands), is not working.  He starts shaking his head no.  Much to my bewafflement, the XYL reaches in her purse and pulls out another three dollars.  She hands the money to him.  The frown corner on his face lightens a little.  “OK” he says, but no excitement is attached to his words, “I guess that’l do.”

Figure 2: Obviously it’s NOT a PTO tuning unit.  The tuning pulley could use a rust-rubbing

At home I wondered,  “Was it too much?”  Like most hams with new junk, I couldn’t wait to “fire it up.”  Like most hams, I bypassed the warnings that tell you to expect fire if you “just fire it up.”  The rush hadn’t completely receded, subconsciousness was still in control.  I flipped the switch on the power supply,  “Thirty five amps at 12 VDC, that should be enough” I amused myself at the overkill. If I were to fry it, it would *really* fry.

The results were like a downhill energy crash after a three cup coffee morning.  No sound.  No lights.  No camera.   No action.  Bummer.  I went to the internet, and searched for some blog items that may give a hint about where to whack it with a hammer.   The words sprang from the page: “The unit does not actually run on 12 VDC.  That only charges the battery, which itself runs the unit.”  Ahaaaaa!  Maybe there’s hope!   Like the second round of afternoon coffee, I was again hopeful that my junk could be joy.

I peered more closely at the little transformer and the power supply circuitry.  Indeed, the transformer looked too underpowered to be the unit’s main power source.  It was there only to trickle charge the battery when connected to AC mains.  I traced a wire to a metal cylinder, which in a first glance I had mistaken for a power supply capacitor.  Instead of capacitor, it was battery.  Eight old, long dead, NiCads were inside of it.

I quickly dialed the big ole 35 amp power supply on my bench down to the level of eight NiCads (9.6 VDC).  I noticed the speaker was missing from the old GR-78, so I connected an external speaker from my junkbox.   Anticipating success already, I pulled the built-in whip antenna to its full extension.  I pulled the +plus power lead from the charging port, and alligator-ed it into the power circuit, bypassing the charging fluff.  I snipped the long-gone fifty year old NiCad tube, and pulled it from the old radio.  Again, I twisted the on/off button.  The howl of an AM shortwave station lit up my ears.  Yessss!

Was it really a lucky howl of screeching carrier that I heard, or the lovely wail of the boat anchor siren.  I was soon to discover, which was which …

I found the SSB/AM switch and flipped it to the “AM” position, which resulted in a much more soothing sound, even if it was Chinese.  I tried to turn the main tuning knob.  It was nearly frozen.  I then tried the band-spread knob.  It was completely frozen.  Was the radio worth what the flea market merchant begrudgingly received in exchange for it, when it could only receive one Chinese station?  I thought for a moment.  Could it be an inductively tuned unit, like the Ten Tecs are?  Oh Noooooooooo!  Not a PPPPPP TTTTTTT OOOOOOOO!

I peered down at the string of the dial, and followed it back to the tuning caps.  Nope, not a PTO.  Whew!  Don’t get me wrong.  PTOs are great, unless you have a frozen one.  I found a small wrench and loosed the thru-chassis shaft that coupled the main tuning knob.  I rubbed some lubricant into the recess, and retightened it.  Now, the tuning dial spun freely.  The heavy pulley on the shaft gave it momentum, and when I spun the dial, it could go on after I released, but only a little.  I lubed it some more.

Figure 3: Bandspread shaft needed some TLC

Finally, I could move off of the Chinese station.  My interest turned to the band-spread knob.  Its troubles were exactly like the troubles of the main tuning knob – excepting that it required a little more lubricant to free the old thing from its forty or fifty year accumulated frozen state.

I spun the dial over to 7.030 MHz.  The CW lit up my ears.  It’s a lucky thing, you know, to be older than the old GR-78, and to have trained my inner-brain CW filter, for over fifty years, to handle the selectivity of this old radio.  Three CW stations chirped at once, each separated by only a little shift of frequency, but I could move from one to the other, and copy each independently, without much effort.  Maybe this thing COULD be useful, I mused.  Maybe it’s a throwback radio, to take us back to the most challenging of operating scenarios – that being the novice era of crystal bound transmitters and really poor receivers …

But, that’s unfair.  The G-78 doesn’t appear to be a really poor receiver, but I don’t think it’s a great one either. One needs to keep ones expectations in check.  I think it’s more suited to the wide AM signals of the shortwave bands than to the amateur segments.  I’ve already had my ~20 of ham fun with it, so have no complaints. Actually, I found the sensitivity of the old girl to be pretty decent, once I figured out that I could flex the whole thing in my hands to get “high sensitivity” to kick in.  Of course, the necessity of the gorilla-handling technique was a pointer to the underlying issue, which turned out to be the band switches.  Those too, lie dormant for fifty years, making them as vulnerable to the oxidation of the ages as were the tuning knob thru-shafts.

I put a video up on YouTube where you can see the old radio and hear me talk about it:


There’s a little bit section in the video where the radio is playing some CW, although the recording was made during a contest, and I think the old thing was getting a little overloaded.  Normally, it sounds a little better than what was recorded in the video.

Figure 4 : Main tuning shaft needed some TLC.  Note easy adjustments of trimmers/slugs

So, a little contact cleaner may be just what the doctor ordered.  Maybe some Windex could be used as well as the contact cleaner, as the plexiglass panels of the tuning window clearly show their own fifty years worth of dust and debris collection.

Read More about the fifty year old Heathkit GR-78 …