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Tonight I began work on the Hammarlund HQ-129-X I bought a couple of months ago. Tonight I just took it out of the steel rack case, and began to survey what I will have to do. Here are the front of the set, a view of the top of the chassis, and a view of the underside of the chassis before I do any work...
[Image: https://64.media.tumblr.com/638da1f1420d...60ca64.jpg]
[Image: https://64.media.tumblr.com/13688b8ebbb2...3ca9c7.jpg]
[Image: https://64.media.tumblr.com/59583ba145c0...698ab8.jpg]
First order of business, order a 3 section 10-10-10 MFD 450VDC can type electrolytic condenser.
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Tonight I began working on the HQ-129 some more. I have decided not to use a can to replace the 3 section can electrolytic, but instead to mount 2 terminal strips and use individual 10 MFD 500V condensers. Cheaper, and will be easier to service in the future, and actually allows higher voltage condensers for even greater reliability.
To be able to get at things, I will need to remove various parts, including the headphone jack, so tonight I removed the knobs and the front panel. From the color scheme used this appears to be an early production HQ-129-X. Except for having the original antenna connection replaced with an SO-239, and a few other minor back panel modifications, it is pretty much unmolested, except for one puzzling modification. Someone added a 7 pin miniature socket in the back corner near V11, the OC3 voltage regulator tube. It is connected to a SPST switch on the front panel, also an addition, which is labelled "CALIBRATION". There was no tube in the socket when I got this radio, although all the other tubes were there. The original RF tube, V1, which should be a 6SS7 seems to have been replaced with a 6SG7 on purpose, since this number is written next to the socket under the chassis. I am rather puzzled about this socket, since there is no sign of a crystal to go with it if it is a calibrator modification. Here are pictures, and a schematic. If anybody has any ideas about it, let me know. I just bought a Hammarlund FS-135-C so I will be able to use that as an internal calibrator if I wish.
[Image: https://64.media.tumblr.com/d0ffbe7d814b...be77fa.jpg]
[Image: https://64.media.tumblr.com/cfc79603535a...d3772f.jpg]
[Image: https://64.media.tumblr.com/1c2c7be38ec5...a6c710.jpg]
[Image: https://64.media.tumblr.com/dd33d2c3e077...df03f6.jpg]
(This post was last modified: 12-06-2021, 10:32 PM by mikethedruid.)
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Keep finding more things ! The volume control with switch was replaced with one that is NOT right. I just ordered a correct one from Mark Oppat.
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Looks like the 7 pin socket might have been for an external crystal calibrator. There is no way that a tube plugged in to that socket. Perhaps a previous owner built a separate calibrator box and connected it by a cable to the 7 pin socket.
It appears the socket provided 6.3V and B+ for the calibrator along with a connection to the antenna circuit and provision for the switch to turn it on and off. That's exactly what would be needed to connect an external calibrator.
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Interestingly, the same vendor who sold the HQ-129-X was selling the FS-135-C, the CHRS as a fundraiser. I wonder if the two originally went together? Well, I'll find out soon when the calibrator arrives.
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Work continues on the HQ-129-X. Somebody replaced the volume control with an incorrect part. I have ordered a proper potentiometer with switch from Mark Oppat. I replaced the two condensers inside the BFO can, but have left others in that area until I get the potentiometer.
[Image: https://64.media.tumblr.com/1774c9eb8860...539647.jpg]
I have gone on to replace most of the rest of the paper condensers. There are a few on the side of the chassis away from the power transformer, choke, and output transformer which are a bit tricky since three condensers are mounted between two terminal strips to which are attached several resistors. There are two places where they did this. Being careful, this was not too difficult. All 6 of these condensers were .02 MFD, 600 volt. Hammarlund seems to have used .02 MFD condensers in most places where other manufacturers would use a .01 MFD.
[Image: https://64.media.tumblr.com/300ad48af7e6...f138c8.jpg]
Here is a view of the whole underside of the chassis as it stands. I won't be able to do much more until I get the parts I have ordered.
[Image: https://64.media.tumblr.com/0fda51aab224...31b41d.jpg]
YES, that is a blown up .05 MFD 600 VDC condenser, bottom, near the center. It was one of the ones going between each side of the power input and chassis ground. Its replacement is one of the parts I am waiting for. I don't have any .05 MFD safety condensers.
(This post was last modified: 12-11-2021, 04:32 PM by mikethedruid.)
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Tonight I tested all the tubes. I started out testing them using my Simpson 305. They all tested good except the 6SG7. I had another 6SG7 in stock, so I tried that and it also tested bad, which I found very odd since it was boxed and had I had tested it recently and it was GOOD. Now, all the 6SS7 tubes had tested good. These tubes have the exact same pin out. They are also very similar pentodes. Oddly, the settings in the Simpson 305 list are somewhat different between the two. I tried testing it as a 6SS7, but again, it tested bad. Finally I tested it on my Eico 628, and it tested fine, as did the other 6SG7. Interestingly, the Eico does not list the 6SS7, but, when I tested one of them using the exact same settings, it also tested good.
6SG7 data sheet
6SS7 data sheet
At any rate, I have a full set of good tubes to use once I get all the rest of the problems sorted out.
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As is usual the original tuning knobs have been removed, replaced by an oversized pair of Dakaware knobs, or whatever, don't forget to check the resistors, those rough finished carbon comp jobs are junk. A lot of post war sets use those and they are second only to dogbone resistors for drift, sometimes even worse.
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The reason why companies used carbon composition resistors in those days was because it was a choice between those or wire wound. Modern types were not commonly available until the 1990s. It was a matter of cost also. Wire wound were much better at maintaining their proper resistance over a long period, but they were also MUCH more expensive, so in most cases carbon composition resistors were the go to choice. I checked the resistors and they have actually stayed within tolerance except for a few. Interestingly several 2.2K resistors have drifted just over their 10% tolerance (silver band). Besides that, only one 4.7K was beyond its tolerance. Hammarlund was usually quite good about using good quality parts. They were considered top of the line in their day, and had a reputation to uphold.
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Today I removed the 7 pin miniature socket modification, and rewired things in preparation for when my Hammarlund FS-35-C arrives.
[Image: https://64.media.tumblr.com/6f17f635718e...9f0b17.jpg]
I also replaced the 4 section electrolytic condenser can, 10-10-10 MFD 450 V and 20 MFD 25V, with one I had in stock 20-20-20-20 MFD 475 V.
[Image: https://64.media.tumblr.com/c04d505e8565...d08c2a.jpg]
I put the clip back, but have not re-mounted the can because of the volume control work I will have to do. I suppose the next thing I will tackle is cleaning off the topside of the chassis which has quite a layer of grimy dust on it. I really can't do much more until more parts arrive. If, by some remote chance, we get a fairly warm day, over 60F, I may take a wire wheel to the outer cabinet, then prime it, and give it a fresh coat of silver paint. I am reluctant to repaint the faceplate or the cowling that goes around the frequency dials and S meter. despite some scratches and wear. The faceplate is the light grey with "Hammarlund" and "HQ-129-X" in RED lettering, and the cowling is the original light blue, which marks this as one of the first run of this somewhat historic radio.
(This post was last modified: 12-09-2021, 08:13 PM by mikethedruid.)
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Heard from Mark today and he's making my volume control, went to his site, and completed the order and paid him. I can hardly wait until it arrives. In other news I replaced the power cord last night, but I am waiting until the safety condensers I ordered arrive to hook it in, and also for the volume control with switch to connect the other side, since that is where it goes. So, now I just have to be patient.
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Fortunately I didn't actually have the power cord connected to anything yet since I decided to remove the plate a previous owner had screwed to the back when they did their "modifications." Why they went about them the way they did baffles me. Instead of buying a small aluminum chassis box, only a few bucks back in the Radio Shack days, and an SO-239, and a 300 to 75 ohm ballun They went to the trouble of removing the old screw type connectors for the speaker and the antenna, then making and mounting an aluminum plate to cover the old connector holes on the back of the chassis, and then add an SO-239 which was connected directly to one of the old antenna leads and chassis ground. They also removed the old speaker connections and replaced that with a 1/4" phone jack. Again, this could easily have been added to that box and the back of the radio left unmolested. The metal work was not badly done. The electrical work left much to be desired, cold solder joint on the SO-239, etc. All in all I am beginning to understand the double entendre of the term "HAM handed." I have appropriate screw type terminal strips coming so I can return things to something like normal again.
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Hooray ! Today my order of parts came in from Dave Cantelon at Just Radios, including the .05 MFD safety condensers, so I was able to install those. Now I am waiting for the terminal strips and the volume control. Progress is being made, slowly but surely.
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It isn't all carbon comp resistors, it's those post war ones with the rough finish, whatever make they were, that drift like crazy, I even had some NOS ones that had done this. Sand resistors are wire wounds and those are definitely replace on site.
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It's been a while since you saw this thread, huh? Too long for me also. Well, today I used my cane, and went into my radio room, sat down at my work bench and did some more on my HQ-129-X. I replaced the audio gain control, and then put back the cover for the BFO, the electrolytic can, and the headphone jack. I also mounted the 3 screw terminal strip for the antenna and ground connections. I haven't wired it yet though. The person who owned it last had converted the antenna to an SO-239, and used only 1 wire going to the connector, instead of the two as the original. I have rechecked the schematic and made a much clearer version which I can print an enlarged section from to hunt down things and make sure I connect everything correctly when I go back tomorrow or the next day. It felt good to be able to get back to work on it after about a month and a half away.
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