The Hammarlund HQ-129X is the post-war successor to the HQ-120X. The first ads proclaim the HQ-129 to be "essentially the same as the HQ-120 but has several improvements and modifications". A prototype HQ-129X that looks like a modified HQ-120X appeared in the November 1945 full-page ad in Radio News (page 24). The first picture of the HQ-129 as manufactured appeared the following month (December 1945, page 24). Note that the ad makes it obvious that the price matches the model number.
A review article with a discussion of the noise limiter circuit can be found in QST magazine, June 1946.
The HQ-129X is a solid well-designed radio that purposely splits the bands, including the AM broadcast band, so that the amateur radio sections of the shortwave bands will be favored. A special tuning cap assembly was designed specifically for the receiver featuring 6 tuning cap sections and 9 bandspread cap sections. The bandspread is marked with the 80 to 10 meter ham bands. The very simple fly-wheel-weighted twin tuning controls and mechanics of the HQ-129X are among the easiest to use and have about the least backlash of any communication receiver I have experienced. There are no dial cords or springs to stretch and break. The build-quality and electronic design of the HQ-129X make it one of the best in the era for the money (at least if bought before that 28% price increase!)
Except for those wimpy knobs
The vast majority of the HQ-129X receivers I have seen have the tuning knobs replaced and often the RF and audio gain control knobs as well. Owners of the HQ-129X replaced the knobs with larger, heavier ones for a more solid "feel". Even the prewar HQ-120X knobs are more substantial than those of the HQ-129X. Other than perhaps for a changed cosmetic postwar look and feel, probably at the recommendation of the front-panel designer, I always wondered why Hammarlund went with the light wimpy knobs.
Hamfest conditions
I had repaired a couple of these sets some years ago. This example appeared at a regional hamfest (ham radio swapmeet).
It was in rough condition especially its cabinet which was two-tone green and rust.
Repairs
The schematic can
be found at EB5AGV's site at this link . The manual can be found on the BAMA site. See my homepage for a link.
This set came with a broken power plug. That was not a problem since I planned to replace the power cord anyway with a new three wire cord. I powered up the set slowly, but the electrolytic would not reform. In fact it started to get warm indicating serious leakage. I replaced it with a new-old-stock electrolytic that tested fine and reformed almost immediately. The original cap was three sections of 10 MFD and a low voltage cathode bypass section. The replacement had four sections of 20 MFD and was about the same size.
The RF gain control was not working as it should. Deoxit did not help. On opening it, I found a broken spiral wire inside that connects the moving contact to the center terminal. Soldering the wire to a proper spot on the moving contact solved the problem.
I noticed that the volume on the set was quite low, even though the S-meter was reading full-scale on stronger signals. There are only three tubes in the detector and audio chain. The 6V6 and 6SN7 were in good order. The problem turned out to be a very weak 6H6, a problem I have only experienced once before. Replacing it brought the volume level up to expectations.
I replaced all of 0.02 capacitors, most of which were used in high voltage applications such as screen grid bypass caps. I also replaced several resistors including one that was cracked in two. I left some of the 0.05 MFD original caps in the set. Those are used as bypass caps in the low voltage cathode circuits where a couple of megohms of leakage will have no effect on the circuit. The radio even has a 0.05 cap across the audio secondary (across the 6 ohm speaker line). I could think of no logical reason to replace it. Leaving a few of the original caps in selected low impedance, low voltage locations keeps just a bit of the original chassis-bottom appearance.
One of the two (non-original) tuning knobs had its crank-handle broken off. I found a matching knob in the "boxe de junque".
The plastic of the fiducials (the tuning windows with the center lines) had yellowed and crazed so that the dials could no longer be seen clearly. Cleaning and polishing did not solve the problem. I made a replacement pair. The original PM speaker was replaced with another one of similar vintage.
Deoxit on the controls and tube pins, lubricating some moving parts, and obviously some paint completed the repair.
Alignment
The HQ-129X, like all radios with a crystal filter in the IF chain, must have its IF aligned to the crystal frequency even if the crystal is not perfectly at the preferred IF, in this case 455 KHz. Note that a full IF alignment according to Hammarlund requires a sweep generator and scope to adjust the pass band.
With the crystal filter switched in, I used an unmodulated signal and watched the S-meter carefully for passage of the signal. The tuning dial was at the bottom of the broadcast band as suggested by the Hammarlund alignment instructions. I reduced the signal generator output so that with maximum RF gain, I could still see the S-meter signal but not overload the IF chain. While watching the S-meter, I tuned a bit up the dial to see if any changes would occur. With no changes to the S-meter reading, I was sure that the receiver was responding only to the signal in the IF chain at the crystal frequency. Taking note of the frequency as displayed on my counter, I touched up the IF chain to that setting. Most of the adjustments were already on or very close. Only one adjustment was a quarter turn or so off the peak. I will revisit the IF alignment at a later date with a quality sweep generator.
I next aligned the RF section. The large easy-to-reach RF section of the HQ-129X makes this part one of the easiest to align among communication receivers. The receiver can be readily set to excellent dial accuracy. The only question I ran into was the 30 MHz setting on the highest band. I had two signals of about equal strength. One was at an oscillator setting that was an IF frequency higher than 30 MHz and the other an IF frequency lower than 30. Which one to use? I went back to the low side of the highest band and tried to adjust the oscillator coil to the tuned frequency plus the IF. It would not align that high. Conclusion, the proper oscillator setting for the highest band is an IF frequency under the dial setting.
The receiver has a modification that connects a thin piece of coax from the converter plate to a back-panel coax connector. Since that modification would be useful for connecting a panadaptor, I left it in. I suspect that may also have been the intent of the original owner.
Performance
I have never been disappointed with a properly working HQ-129X. In fact, I wish I had one when I was first listening to the shortwave and ham bands as a kid. SSB and CW on the lower ham bands as well as the international shortwave broadcasts are easy to tune. The receiver is quite stable after warm up in part because of the voltage regulator tube. Proper RF alignment can make the tuning quite accurate. Moreover, the HQ-129X and its older sibling the HQ-120X are great for broadcast band DX-ing if connected to a half-decent antenna. The radio is conservatively constructed and should give many more years of good service.
The HQ-129X was followed by the HQ-140 and then by the HQ-150. All are excellent sets, but are limited by the single-conversion design. Later large Hammarlunds went to dual conversion for the upper bands.
Previous HQ-129X receivers
As already noted, this is not my first HQ-129X. I repaired these other HQ-129X receivers some years ago. They have appeared on my website from the time when smaller pictures were the norm.
This picture from the cover of the December 1946 Radio News clearly shows the HQ-129X model number on the panel in red-orange. The photo depicts the radio being assembled in the Hammarlund factory. Because of this picture, I am assuming that the red-orange color is the oldest version.
Here's a link to Jim Hanlon's excellent review of the HQ-129X in the Old Timer's Bulletin .
1998, updated 5-5-11
Zenith 5G500 and 6G501M Universal 3-way portables
with "Wavemagnet" antennas were the previous items on the bench.
