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Cobalt RaQ3 | Gentoo APRS Ebuilds | Heathkit GR-54 | J-Pole in a tree | Milk Jug Dipole | Power Supply | Workbench

Improving my Heathkit GR-54 Receiver

   Ultimately I intend to build my own receiver and transmitter for the HF ham bands however I do already have one radio capable of receiving them.  I have an old Heathkit GR-54 communications receiver.  My GR-54 does function however it has a few issues which would make it difficult to use for very long.  It has a very loud hum which is always on even if the radio is in standby and is not attenuated by the volume control.  It tends to drift making constant adjustment necessary to stay on a narrow SSB signal.  Even the wider AM shortwave broadcasts require tweaking the knob every few minutes.  This problem is compounded by the fact that the fine tuning control tends to stick.

   For the hum I'm pretty sure a recapping is what's necessary.  This radio seems to be all original parts except for a SO-239 which somebody stuck on the back of it.  There is a large metal can quad capacitor in it as well as a large paper one.  They all seem to be part of the power supply filter.  I was going to restring the fine tuning control but the current string seems to be quite tight.  I suspect that the problem is in the bearings in the fine tuning capacitor.  I will have to look into this more.  As for the drifting, the tricky thing is that I'm not sure what I should even expect.  I do realize that an older radio like this is not the same as the modern PLL or DSS boxes we have today with their digital displays and computer control.  I suspect that some of the drift is just normal. Still, I doubt that it should drift this much and it would be very difficult to use for ham radio as I would like to.

   One of my first thoughts about working on an older radio, especially a Heathkit is that it could be a collector's item. Therefore I should probably try to restore it as close to possible as original rather than just fix or upgrade it.  As I mentioned this radio has already had a UHF connector added to the back.  I also checked the completed items on EBay multiple times.  This radio seems to be quite common but not in demand.  It doesn't always sell at all and when it does it hardly sells for enough to be worth the shipping.  I've decided it is ok to mod this one a bit though I won't be going too far with that... I'm not going to transistorize it or add a DDS module or anything like that.  I may add a jack in the back to get at the local oscillator so I can hook up an external frequency counter though.  I haven't decided on that one yet.

   Once I decided it's ok to mod it a little I searched Google to see if there are any well known mods already out there.  It turns out there are 6 of them.  I see the same GR-54 mods published in multiple websites but it looks like a David Childs originally collected them together.  I want to give credit where it's due, I think this may be the original site but I don't know for sure. He found one of the mods in Popular Electronics magazine, I'm not sure if he came up with the others himself or just collected them.  He doesn't explain the goal of each mod but if you look at number 4 it involves adding a regulator to the local oscillator's power supply.  That one really interests me because I'm hoping it will cure my drifting problem.  It was that mod which made up my mind I will go ahead and do the mods as well as the repairs. My goal is to avoid modern looking parts, gut the old capacitors and stuff the new ones inside them so at least it doesn't look modded.

   This is going to be an ongoing project for me, I intend to do it in parts, use the radio in between and write about it as I go.  I also found most of the manual in a PDF file including the alignment information so I can re-align the radio once I am finished.

May 18, 2009
   As I wrote about in my blog I started the project by searching the bins at Dayton.  I found most of what I need to get it done but not quite what i wanted.  To replace the metal can capacitor I needed 3 40uf and 1 20uf caps.  Power handling varies from about 250 to 350V. Unfortunately all I could find were 47 and 22uf which were way to big to fit all in the can.  I figured those values would probably be ok but I kept looking.  By the time I gave up and tried to by those ones many vendors had packed up and I was only able to get the 47uf ones.  I decided to use 2 47uf capacitors to make a 23.5uf one but that means it's all that further away from being able to fit in the can.  i decided to mount these in the bottom of the chassis and leave the old can in place.  It's not as good as restuffing the can but at least one can take the top off and still not see the modern electrolytics.

   The paper capacitor is also 20uf 350V.  It would be hard to leave it in there for looks while replacing it below because it is on a PC board and I would have to cut traces.  Fortunately part of the regulator mod involves replacing it with a much lower value capacitor.  I found a .22uf which should easily fit in side the old paper one's body.  There is also a resistor to replace with that mod.  A 3 watt 15k resistor gets replaced with a 5 watt one to handle the extra current drawn by the regulator tube.  All i found for that was this large green thing.  I don't know what type it is and I'm a little concern that under the green coating it might be a wire wound resistor which would add inductance and cause problems.  It was the best I could find though so I will just swap the resistor as the first part of that mod and see if it works before I continue.  If not then I will just have to go online and buy one.

June 16, 2009
   Today I finally cracked open the case and started making changes to the radio.  There was no good place under the chassis to mount all 5 of these new large electrolytics.  i needed to create a new mounting spot for them so I placed them on a piece of perfboard.  Before I started mounting parts to the board I wanted to know how I was going to mount the board to the chassis.  I decided I would bolt it to the chassis on one side but I didn't want to try to go the whole way across so I would need it to be able to support it's own weight on the other.  I decided to use use a narrow piece of board which could fit on the under side of the chassis on it's edge.  I cut the board to size and then for a mounting bracket as well as support I pop riveted an old computer slot filler to it.  I didn't want to use the normal screw notch in the slot filler so I also drilled a hole through the tab so I could bolt it to the chassis.  

Testing the GR-54 Recap
Photos courtesy of Photos by Aliesha
   I was surprised to discover that solder sticks well to the metal the slot filler is made of.  This worked out well as the negative sides of the capacitors all go to chassis ground anyway.  i just lined them up right with their negative leads against the metal and soldered them on.  Now I only had the positive sides to worry about making connections to.   The positive leads of the capacitors get connected together through resistors.  The resistors were soldered directly to the original capacitor.  I removed these and put them on the perfboard as well.  i also removed all the wires going to to original capacitors and labeled them temporarily with some leftover painter's tape. 

   Remember when working with large capacitors.. always discharge them first!  I did this by clipping one end of a test jumper to a large plastic handled screwdriver and the other end to the chassis.  Then i touched each terminal.  I've been pretty careful to do this each time yet i already managed to get a spark out of the old capacitors once when I thought they were already discharged.  I haven't received any shocks from they yet though thankfully.

   I was going to just re-run the wires away from the old capacitor to my new board.  They are bundled together with other wires pretty well though and I didn't really want to mess with it.  Also, I decided that I should have some sort of plug on the new capacitor board so I can remove it easily.  Otherwise it would be in my way as I do the rest of the mods.  I decided to add a terminal strip next to the old capacitor can to run the wires.  I'll also solder the cord to go to the capacitor board there.  I didn't really have room left on the perfboard for a socket so I need a connector with wires on both sides to meet halfway.  I decided on using the connectors from an old computer fan and a computer power supply.

   Unfortunately I only have a 2 terminal strip available in my junkbox and I need at least 4.  I found a 10-pack of 5 terminal strips on EBay and ordered it.  Meanwhile I was very eager to see the radio work with my new, not-quite the correct value capacitors.  I connected the capacitor board temporarily with jumper cables and fired it up.  It works!  there is still some hum but it's quiet enough to not really be a bother.  Hopefully it will get better yet when I replace the paper capacitor but even if not this is usable.

June 20, 2009
  The terminal strips arrived today!  I really didn't think I would see them before Monday.  They look good but I don't have time yet.

June 21, 2009
   Monroe Hamfest was today.  Guess what I saw there... Why did I order terminal strips off of EBay again?  I just felt like donating to the post office maybe?  I should have known better but just was being impatient. Oh well... I mounted the terminal strip with a couple of pop-rivets and soldered everything in.  The strip just barely fit. I could have gotten some 4 terminal strips which would have fit better but whenever I pay shipping on such small, inexpensive items I like to get a pack to have for future use.  I figured I can always substitute 5 terminals for 4 but not so much the other way.  I nicked the mounting tab for the power transformer when I drilled my holes, it was such a tight fit.  Oh well, no real harm done.  I soldered on my connectors and bolted the capacitor board to the chassis.  It still works!  Tuning around a bit more I heard fewer stations and had a hard time getting the SSB signals tuned right.  I am using a 20 meter dipole which is a daytime band and it was close to midnight so hopefully it was just because the band wasn't open.

June 22, 2009
   Tonight I tuned around for about 1/2 hour after work while it was still mid day. It seems like I might be having just a slightly harder time getting SSB signals tuned right but it's not bad.  Could changing the values of the power supply capacitors do that or is it in my head?  i did get plenty of signals from plenty of countries including Ireland and Venezuela so I am happy it is working.  It even seemed like it is drifting a bit less. Is that possible?  I will still go ahead with the rest of the mods though.  While I was tuning I put some model train lubricant in the fine tuning capacitor's bearings.  At first it actually got worse but as I use it it gets better.  It still sticks a bit but it's much better than before. Once I was convinced I haven't broken my radio I left it for a while to go fix the A/C in my car.

   Later I started on the power regulator mod.  I have the power regulator tube as well as as socket for it.  I wanted to mount the tube on the main PC board because all the other tubes are mounted to PC board, not to the chassis.  The main board is where the Osc B+ filter cap (the big paper one) is so I can hook it into the Osc B+ line there.  It also has a large open area available to mount it in.  The only issue was that I was apprehensive about cutting the hole in such an old piece of PC board.  I was afraid I might shatter it.  I drilled it out slowly and carefully though and managed to mount the socket without any cracks. After that I ran out of time, so I checked real quick that it is still working and called it a night.

June 24, 2009
   I installed the 0B2 voltage regulator today.  The receiver is much more stable. I can actually tune in an SSB station, take my hands off and listen for a while!  I love using this radio in the dark with the top off with all those tubes glowing inside.  The 0B2 with it's nice purple glow is a great addition.

  This mod consists of 3 parts.  The 0B2 voltage regulator tube is installed across the oscillator B+ line and ground.  It acts much like a zener diode to keep the voltage stable.  Because it increases the current draw the 15K 2Watt resistor which performs the voltage drop for this line has to be replaced with a 5W one.  Unfortunately I did not find a 5 Watt resistor at Dayton but I did find a large green tubular 15K resistor which did not have a wattage marked on it.  I'm pretty sure they had this style resistor when the radio was made but I'm not sure they used this shiny green coating.  There goes the vintage look but that's ok, I think I may replace this resistor again soon anyway for another reason I'll get into shortly.

   The third part of the mod is to replace the big paper 20uf filter capacitor with a lower value one, .somewhere between 22 and .47uf.  I picked up a .22uf capacitor at Dayton. This was actually why I chose this mod next because it completes my recapping project.  I removed the old "paper" cap and put it in an old frying pan which we don't cook on anymore.  I used my heat gun to melt the wax and pulled out the insides.  It turns out that all it was is an aluminum can electrolytic wrapped in wax and cardboard.  I filled the old cardboard tube with hot glue and put my new capacitor inside.  The 20uf value was printed on the outside.  I didn't want to try to change that and mess up it's looks so I put a piece of tape on the bottom with the new value and power rating.  The tape isn't visible now that it's soldered back to the board but if anyone tries to replace it later they will at least see the true value then.  In retrospect I probably should have used paraffin as that would be much easier if someone tries to recap it again in 20 or 30 years.  But, then again, what are the odds of that?

   The reason for lowering the capacitance is that the local oscillator pulls different amounts of power at different frequencies.  At some frequencies, especially the highest ones, around the 10 meter band it can pull enough power that there isn't sufficient left for the 0B2 voltage regulator.  This can cause it to become a relaxation oscillator.  Unfortunately, even though I lowered the capacitor mine still does this about 1/2 the time if I try to tune the 10 meter band.  I get a nice squeal when this happens and if I pull the tube the squeal goes away.  So far the radio hasn't performed very well above about 20Mhz anyway but I am hoping that will get better as I work on it.  I'm thinking I may try replacing the 15k resistor with a 12k one to see if this gets better.  There aren't any nearby hamfests for the next couple of months so I checked EBay.  I found a guy who had a 12K 5Watt resistor as well as a 100 pack of 47 ohm resistors.  I still needed a 47 ohm 1/2 watt resistor for one of the other mods and it was cheaper to buy his 100 than most other auctions for small numbers so I bought them both.  I have some pictures I will come back and post soon and I'll perform and write about the next mod sometime after the resistors arrive.

July 5, 2009
  Today I performed mod 3 from the list which was replacing the rf and first if amp tubes with 6DK6s. It also involved replacing the two 470ohm cathode bias resistors for the first if and mixer amps with 47ohm ones.  This seemed to go ok.  I'm not entirely sure but I think it might be receiving weaker signals.  It's hard to tell given the variability of band conditions without expensive calibrated lab equipment to check it.  I did notice that the 6DK6s have much brighter filaments and run much hotter. This concerned me a little at first but after leaving the radio on for a few hours I am satisfied that all is well.

   Next I replaced the big ugly green 15k resistor which I wrote about last time with a nice little 1.2k one which almost looked like it belonged there.  Yes, you read right, 1.2k.  Somehow I bought a 1.2k resistor while reading 12k in the description.  Then I mounted it in the radio still reading 12k all the while.  Fortunately the 0B2 managed to divert the extra power to ground without burning up.  It did get very hot and much brighter than before.  I was checking out the 0B2 when I noticed that the new resistor was getting very hot and starting to discolor a little.  Only then did I notice that it was only 1.2k!!  For now I have the big ugly 15k resistor back in place.  I think I will wait and see if it still oscillates on 10Meter after the radio is all tuned up before I try to replace it again.

  As mentioned in the mods list, I did find that I couldn't tune the BFO low enough for LSB.  The mods list recommended replacing C48 with a 3-30pf trimmer cap.  I did have some trimmer caps on hand that looked the right vintage but they do not have values marked on them and I have no way to measure capacitors that small.  Instead I opted for a little green 3-30pf trimmer cap which I picked up at Dayton just for this project. Unfortunately I haven't stuck to keeping the radio looking authentic very well but I suppose it will with the case on.  This worked and I can receive LSB better than ever.

  I also noticed that I missed an electrolytic.  I missed C53, a 10uf capacitor which goes from V6B, the audio output half of V6 to ground.  Hoping that replacing it might eliminate the remaining hum I decided to replace it.  I still don't have any 10uf capacitors on hand so I ordered a package of 20 off of eBay.  I couldn't see the voltage rating given how the capacitor was mounted and I only wanted to remove it once due to there being a lot of wires in the vicinity on the solder side of the board so I measured the voltage at the capacitor with a multimeter.  It only measured about 10v.  I saw a 20 pack of 25v ones on eBay so I bought them.  They don't really look right for the timeperiod of the radio so I might either try to paint one black or just mount it on the underside of the board.

July 18, 2009
   Unfortunately the first batch of capacitors I ordered didn't make it through the post office.  Even though the seller did pay for them to be sorted by hand they went ahead and put them in the sorter anyway.  All I received was an envelope with scuffmarks on the outside and a receipt inside.  The parts had been squished right out through the end of the envelope.  I've seen this happen before when we sent stuff out from the Toledo post office.  I bet it happened at that end.  It amazes me that they bother to deliver the envelope anyway after destroying the contents.  The seller was very nice about this and shipped me another 20 capacitors, this time in a thicker envelope.

   Looking at the great big green tubular resistor I had already added to the top side of the PC board and also the little green trimmer I decided to just solder the new capacitor into place as is and be done with it.  I did so and gave the radio a try.  I turned the volume all the way up and yet still had almost no audio!  It turned out i had accidentally desoldered one of the jumper wires on the back of the board.  Once I hunted down where it went in the schematic I resoldered it and the radio came right up.  Unfortunately the hum did not seem to change.  Oh well... I do intend to actually use this radio so I am glad to not have any old electrolytics left in it waiting to fail.

   I decided to skip mod 1 from the list which was removing the loading resistors from the band 1 and 2 coils.  Those bands are pretty much unusable when my computer is turned on and I think doing that might make them even worse.  Also, they are on the bandswitch boards which I am not sure I want to mess with.  Shannon, KA8SPW warned me about the bandswitch's tendency to come out of alignment so as long as mine is aligned I don't think I want to tempt it.  Mostly I intend to use this radio on ham bands anyway.

   Being done with the mods all that is left is the alignment.  I have an old Heathkit signal generator that Chris, KC8UFV gave me.  I started the alignment procedure "with test equipment" as outlined in the Heathkit manual.  Unfortunately the signal generator was putting out signals not just on multiples of the operating frequency but also on lower frequencies as well.  I was making things worse by trying to tune with that so I switched to the "without test equipment" directions and tried to use the WWV signals.  For the most part I got everything working quite well.  My one problem was band C.  I had messed that one up pretty bad before i gave up on the generator and now I couldn't even find WWV.  I could find a couple of shortwave stations but I had no luck identifying what frequency they were actually on.  I will keep trying, hopefully there will be a band opening which will bring in WWV on 2.5MHz stronger or at least bring in a shortwave station which actually broadcasts it's frequency.

July 25, 2009
   Today I finally managed to identify the frequency of one of the shortwave stations on band C.  It wasn't really on one of the tick marks on the GR-54s display but I aligned it as best as I could.  Once this was done the radio was much more sensitive and I actually found WWV near the 2.5MHz mark!  At this point I repeated the whole alignment procedure for band C  using the WWV signal.  Now it is working pretty good.

   Finally I replaced the cover on my GR-54.  It seems like the hum got a little worse when I did that.  Oh well, it is still bearable now which is a great improvement from before.  The radio still drifts a little but now I only have to adjust the tuning every few minutes where before it was a matter of seconds.  I think it seems to be a bit more sensitive then before too but it is hard to say as I didn' t use it much before now on the current antenna. This project did not go perfectly but overall I would say it was a success.

   I was a little sad to put the cover back on as I liked having the tubes visible.  Maybe someday I will add a case window kit like some people have for their computers.  The two out of place looking resistors and the trimmer cap could be replaced easily enough with ones that better match the era of the radio.  A window hole cut into the case could not be so easily undone.  If I were to do this I think I would try to get a piece of metal bent and cut to act as a replacement top and put the window in that.  Then I could keep the original top stored away intact to allow for easy restoration.  That is not a project for today or even any time soon, it is time to move on to some of the other things I have planned.  My next project from the Dayton list will probably be the "CB" filter.  That should go well with the receiver project I just finished.  Plus it's the only one for which I found ALL of the parts at Dayton.  First though, I really need to get the garage cleaned out to make a better place to work!  Plus, I need to repair the magnet mount I use on my Jeep as it broke recently.

1 Comment - Add Comment

Ed - 2013-12-07 00:34:44 - Reply

Enjoying reading about your project. I found a GR-54 today at the Thrift store. Working, but also in need of power supply caps.