In March 2019 I acquired a long-desired HQ-129-X in decent mechanical and cosmetic condition, for $40. The seller said it was from an estate sale and had been stored about 20 years. The chassis underside was very clean, the bandswitch looked good and there was only a little corrosion on the upper works. The panel shows some wear at the volume control and around the main and fine tuning bezels. It seems to be an early model, with red lettering.
I removed the old can-style multi-section electrolytic filter and installed a quad terminal strip. There, I attached modern 150uf/450 volt capacitors as power supply filters and a 63uf unit for the 6V6 cathode bypass electrolytic. Also replaced were the line cord, AC bypass capacitors, interstage and bypass capacitors. I did not replace any mica capacitors and subsequent testing indicated none needed replacement.
The bandswitch contacts were carefully cleaned with Q-Tips dipped in contact cleaner and a final visual inspection was done. A broken resistor was replaced and a 70+ year-old unsoldered connection was also corrected.
The pilot lights were replaced with LED’s, saving about 300ma of filament current.
After this, I brought it to life slowly using a variac and it worked! Voltages were checked against the Hammarlund manual’s voltage chart and were found to be approximately correct. I let it run for a day and then shut it down and checked the tubes with my old Heath TC-2 tube tester. They were all good!
Then I let it warm up for an hour and gave it an alignment, being sure to align the IF’s to the actual frequency of the crystal filter, rather than just aligning to the 455kc IF frequency. The crystal was nearly perfectly on frequency according to my HP generator and as measured by the station Yaesu receiver.
I am using this rcvr in my shop/shack – it’s the last of the octal tube Hammarlunds. I think this one with red lettering was built in 1946 so it’s only 76 years old; younger than me! It will complement my glowbug 6L6, 807 and 813 transmitters (yes, I also have solid state and digital stuff).
But oops! After it ran for a few days, I turned it on one morning to find that the RF Gain (“Sensitivity”) control had stopped working, leaving the gain running wide open and uncontrollable.
The RF gain control had previously been replaced with a cheap unit so I replaced it with a good quality Allen-Bradley unit that I had. I checked all resistors associated with the RF Gain circuit and all components measured their correct values. The voltage at each tube socket pin matched the manual’s voltage chart specifications. I finally figured out that one of the IF tubes had shorted internally. Replacing it solved the problem and restored proper operation. It took me a while to figure that out since I had just checked all the tubes a few days before. Live and learn.
Connected to a 137 foot doublet at 50 feet height via 450 ohm twinlead, I found that 40 meters was extremely noisy with man-made noise that masked nearly all signals. 40m is swamped with noise on my station’s Yaesu receiver, also.
I had a 400+ foot random wire in a “J” shape running at low elevation through the woods on my one acre lot. I converted this into a roughly shaped “loop” that lies right on the ground and is covered by leaves (it’s in a wooded area) and fed that with 450 ohm twinlead, to serve the Hammarlund.
This on-ground antenna is vastly quieter than the doublet and many stations are now received, making me think that most of the man-made QRN is outside my house. So I think I will use the “loop” as a receiving antenna and the doublet as the transmitting antenna. I’m sure that the patterns of the two antennas will be quite different.
The Hammarlund wants to see a 400 ohm antenna anyway, so the loop’s 450 ohm twinlead provides a good match, and the antenna peaking control peaks signals nicely as we change frequencies, indicating that the match is good enough. The 400 ohm RF input coil indication on the schematic seems odd to me – why not 600 or 300 ohms? But I guess they knew what they were doing.
Note that if you want to use a 50-ohm coaxial feedline for old receivers that want 300 – 600 ohm feeds, you should use a 75ohm/300ohm TV balun to convert the 50 ohm to about 200 ohms. This should provide a substantial increase in signal strength. Of course, the impedance will vary with frequency, but if the receiver’s front panel antenna matching control peaks the signal then it is probably happy with the match.
And finally, I replaced a couple of the knobs with better ones and spray-painted the cabinet, which showed some wear and minor corrosion.
It has been a long time since I used a receiver of this type (I’ve had an SP-600 and an SX-28A over the years), and I had to re-learn how to use the Sensitivity, BFO and Phasing controls to properly tune stations, particularly zero-beating CW signals. But once learned, this rcvr is very good, 70+ years after manufacture.
It’s a bit weak above 20 meters but from 20 to 160 it is more pleasant to use than my Yaesu for CW work. I’m thinking of building a low-frequency converter for it since the Yaesu seems inadequate below 550 khz. But I haven’t tried the Yaesu on the loop on those low frequencies so perhaps I’m not being fair to it.
This set has two B+ filter chokes in a series arrangement in the power supply, with plenty of electrolytic filtering, and as a result, the audio is dead quiet – no hum at all.
7/26/2022 Note: I have just discovered that there IS HUM on the audio output. It is just that my loudspeaker, or very old headphones, can’t hear such low frequencies.
So it’s time to look at the audio circuit wiring to see if it is picking up hum from the chassis or other other areas or to determine where the hum is coming from.
The 3 watt audio is barely adequate, with a 6V6 output tube, and I could actually use a little more volume sometimes.
I have a 2 x 6L6 audio amplifier project in the queue so I might port the HQ audio into that…sometime.
A copy of the manual, including the schematic can be downloaded here.
A copy of the Sam’s Photofax can be downloaded here.