Hallicrafters SX99 Restoration

I received this great old band cruiser from a friend. It is ideal for short wave listening the commercial SW broadcasters. Its wider bandwidth also is nice for listening to the better AM signals in the ham bands. The panel markings were a little worn, but the rest of the radio was well preserved. It even came with a hangar queen (parts unit). I just couldn't resist the temptation to add it to my permanent collection and restored it. Here are some of the tips I can pass along to you.

CAUTION: Working on vacuum tube equipment is fun, but reread the caution on the front page, and get a knowledgeable friend to give you a hand if this is your first time.

The SX-101 was a ham band only receiver, dual conversion, 60 KC lower IF. The expensive SX-100 was similar in appearance to the SX-99, but was a general coverage version of the SX-101. Both of them have good SSB reception due to enhanced detectors. The SX-99 is a single conversion 455 KC IF, two IF stages, one RF stage, so it has less performance than either of the classics noted above. But it does have a built in crystal filter, which adds CW selectivity. The filter is a bit sharp for SSB and not useable on AM, as would be the multiple band width Hammarlund crystal filter designs. SSB reception is OK, but no product detector. There is a way to get a notch by adjusting the phasing control, but it is not as straightforward as adjusting a Q Multiplier accessory. You can add a Heathkit Q Multiplier to this radio if you like, but I did not find it necessary for my use. A Q multiplier is more versatile and easier to adjust than the classic Hammarlund multi band width crystal filter. First, alignment is easier without the crystal filter. Second, if you use the sharpest crystal filter settings for CW on bands 20 meters and above, receiver drift makes tuning touchy. Conversely, with a Q multiplier, you can use the Q multiplier frequency peak adjust for a sort of passband tuning or vernier like the HQ-170 and HQ-180. This is possibly why Hammarlund produced some of its later receivers with Q multipliers in stead of its hallmark multi band width crystal filters. The SX-99 is a very good example of mid to late 50s mid range receiver technology, and a lot like my first commercial receiver, the Lafayette HE-10 (which had no crystal filter and no calibrated band spread). The S-86 was nearly identical to the SX-99, except it was a series string AC/DC set, no filter, no S meter. (Thanks to N2EY for spotting a typo on this model number.) The S-40B is the direct predecessor of the S-85 (no meter or filter, 6SK7 IF tubes). Many of the parts are interchangeable between the above units. Hallicrafters got a lot of mileage out of these basic designs. The SX-96 is a later miniature tube version of the SX-100, but it has dual conversion, and lower cost.

If you see capacitors with stripes like these, they should probably be replaced. A lot of them fail shorted, damaging unobtainium vintage parts. Use the nice orange drops that are available from “Radio Daze” individually or in assortments. IMPORTANT: DO SOME TESTS FIRST. CHANGE THE CAPACITORS ONE AT A TIME AS YOU TROUBLESHOOT. If you just dive in and “shotgun repair” a piece of equipment, you may introduce wiring errors and have no clue where the problem is. I did not need a schematic for any of these repairs or modifications, except for the T/R switching mod. I did use the data from BAMA (boat anchor manual archive) for alignment, since adjusting a radio with the crystal filter type used in this radio is very tricky for the inexperienced. It is better left untouched, and the remaining IF transformers adjusted to match the frequency of the crystal filter. Leave its phasing capacitor half-closed for symmetrical response.

The paper covered electrolytic cathode bypass capacitor shown here was also replaced. I left the electrolytic multi section electrolytic can in place, so that top of chassis appearance would be original. Some people put the new capacitors inside the old can. You can order new replacements that are done this way from sources online. I wanted it to work like new, but did not feel it necessary to go to this extent to make it look original under the chassis.

One electrolytic filter capacitor was bath tub seal glued to the back panel. Then I added a new terminal strip, soldered to one of the old can leads for ground. This made it easy to neatly connect the old and new parts. IMPORTANT: DO NOT JUST PARALLEL THE NEW CAPS ACROSS THE OLD CAN. This works fine for open electrolytics, but later they fail shorted. You MUST disconnect the old electrolytic completely for a reliable repair.

One of the striped capacitors was in a tight spot near the front end. I used an orange drop.


Many radios saved money by not having a fuse. I added a fuse holder, using an existing chassis hole. I also added a thermistor type tube saver to slow start the radio in series. This shows the mounting method. It would also be advisable to replace the power cord with a three wire grounding type cord or at least a polarized 2 conductor plug. This is NOT an AC/DC set like its cousin the S-86, with its dangers.

I recommend CAIG DE-OX-IT to clean the switches and controls without damaging them. Cheaper contact cleaners can contain solvents that destroy the plastic. Beware to clean off all the DE-OX-IT when you are done.


At this point, the radio was playing great. However, I wanted to integrate it into a station with a transmitter. There was no external muting provision. It did have a front panel standby switch. The back cover of the switch was removed. I added a purple wire and routed it to the 600 ohm terminal on the speaker terminal strip. I used only the ground and 3.2 Ohm terminals for my speaker. The 600 Ohm terminal was changed to a new muting terminal for the Dow Key relay spare contacts to operate for push to talk operation on AM. I have no idea why such a capable receiver did not have this feature right from the factory. I did not want to drill holes or add connectors that did not look original. This was the best work around I could devise to avoid spoiling the appearance of this classic.

The Hallicrafters accessory speaker appearance was a bit rough. I replaced the grill cloth with new fabric from JoAnne Fabrics. I consulted ARRL handbooks to be sure I had the right color. I wired around the matching transformer in the speaker. Connecting it directly to the speaker provided the best match for the 3.2 Ohm output of the SX-99. I had to replace the crumbly rubber speaker wire anyway.

This wraps it up. The SX-99 has the classic look of the SX-100, but not the selectivity. It is surprisingly sensitive on the 15 and 10 meter bands.

I plan to pair it up with a home brew 6L6 rig. It will have two 6L6s in the output, bandswitching 160 and up including WARC bands, VFO control. An AM modulator will follow. That work will be posted here. But I have other work first, my favorite Johnson transmitter, the Viking 2. This radio will play nice with that till I get around to the 6L6 rig.


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