Many of the single conversion 455 KHz receivers of the late 50s and early 60s lacked in sensitivity, stability, band spread, and image rejection on 20, 15, and 10 meters. This unassuming box, the HE-73, was the universal fix for all of it, for less than $50. Produced by Trio/Kenwood in April 1963, the new "Heathkit green" styling matched the HA-230; the HA-230 is a restyled HE-30/KT-320. If you can find one, it is an asset to any of the pre 1965 receivers.

On 80 and 40 meters, it is a tuned RF preamp, boosting sensitivity. On 20, 15, and 10 meters, it turns your radio into a dual conversion receiver; on those bands, it can also be used as just a tuned RF preamp, depending on the setting of the function switch. The output of the converter is on 80 meters. If you have a general coverage receiver, full 10 meter coverage is between 3.5 and 5.2 MHz.

This well preserved HE-73 came to me as a swap for services in repair of a Hammarlund HQ-170. I did not expect this kind of performance from such a nondescript device. I was impressed at the level of improvement the HE-73 made to my Lafayette HE-10. I wish I had the HE-73 back when I was a novice operator, to enhance 15 meters, and sensitivity on 80 and 40 meters. I may pair it up with a HA-230, which is styled similarly, and has calibrated band spread.

The HE-73 can be tuned to cover 18 MHz (on the 20 meter position) and 25 MHz (on the 10 meter position) amateur bands without a lot of difficulty. A switch could be added to select different crystals and oscillator tuned circuits, while leaving the RF and Mixer stages the same. If you try this, it is important to realize that the crystal is used on its second harmonic. It is likely you could scrounge this FT-243 crystal from WW2 surplus crystals in somebody's junk box. One way to implement this would be to disconnect the 80 and 40 meter coils, and use the HE-73 only on 20, 17, 15, 12, and 10 meters. The tuning range of the preselector components will allow you to share the 20 meter band position for 17 meters. Please do not write me for advice on how to do this, because I have not done this mod; it is only a suggestion for you to pursue if you like the idea. Due to instability and lead lengths, do not even think about using the HE-73 as a six meter converter. Since I am using this with a general coverage receiver, I can tune to the necessary conversion frequency without the modifications. When something works this well in its original form, I do not feel compelled to make changes.

Restoration is simply replacement of the electrolytic capacitors, the paper capacitor in parallel with the rectifier diode (use a disc ceramic), and the older diode (use a 1N4007). All of these items are located in the "doghouse" in the center. I added a 1 ampere fuse in the AC line inside the dog house, using a fuse clip. There is no excuse for a device that cost this much to not provide protection for the transformer in the event of filter capacitor failure. However, many well known manufacturers of this era neglected this essential feature.

The tune up is fairly straightforward. Use some nail polish remover to clean off the paint sealing the coils. Do not force the tuning screws to clear the paint or you will break the slug at the tuning slot. On 10 meters, I noticed some oscillation when tuned out of band. I replaced the missing tube shield on the RF stage, but it did not help. I installed a 100 ohm resistor in series with the plate lead, but it did not cure the problem. Since all other bands were OK, and the oscillation did not appear when using it normally inside the 10 meter band, I left the unit as it was. The lead lengths to the band switch are self resonant in the VHF region. This is a common problem with equipment of this era. For instance, the HQ-170A oscillates on six meters to the point it is unusable, but it is great on other bands. This was not a problem with the HQ-170, which had shorter leads to the antenna trimmer capacitor.

The manual is available at: https://bama.edebris.com/manuals/lafayett/he73/