Hallicrafters S-120, Refreshed

Hallicrafters S-120 Gets a Refresh

The S-120 resided in my office at work for almost a year until it developed an annoying 60-cycle hum that finally wouldn’t go away once it warmed up. Time to replace the electrolytics.

The Hallicrafters S-120 is essentially the same circuit as the S-38 series: an All-American 5 tube, minus the rectifier — replaced with a selenium rectifier. I bought this swell little radio from a fellow who thought it was dead, except for a few AM Broadcast stations. I brought it home and after a quick spray of Deoxid on the bandswitch and 3-in-1 oil on the tuning shafts (they were almost frozen) within 10-minutes it was working on all bands. Total cost: $10.

Antenna is a ferrite rod, built-in. The rear panel has clips to hold an extending rod antenna — mine is missing. Variations of this model include the SW-500 (same, but a sort-of slate-blue metal cabinet), and the WR-600 (same, but a wood cabinet). It’s a swell consumer-level general coverage receiver, and works great when provided a proper 75-foot long-wire plus a solid ground.

The knobs are plastic, the chassis is separated from the outer cabinet by p

Hallicrafters S-120, Refreshed
Hallicrafters S-120, Refreshed

lastic spacers and screw attachment points — this is a hot-chassis radio. The ‘ground’ in the schematic is actually B-; chassis is separated from B- by C29 and R18 (in parallel). Polarizing the power cord forces B- to always be the ‘neutral’.

C31 – A, B, C, and D – the 4-in-1 electrolytic capacitor sits above the chassis, the same side as the tubes. Unfortunately, there’s no good place to put a terminal strip; plus the leads to the 4-in-1 would have to be spliced to extend above the chassis. So, I relented and put the 4 individual caps near their + connection point; B- is available at several points, which makes this a convenient way to go. An alternative would be to measure this 4-in-1 electrolytic and contact Hayseed Hamfest for a modern replacement. At the time of this writing, they have an exact replacement for the ‘can’ in the S-120.

Updates as of 2008:

  • Replaced the 4 Electrolytics, leaving the old 4-in-1 in place, but not electrically connected.
  • Replaced all the tubulars, basically any by-pass capacitors.
  • Reception is extremely strong on all four bands. Didn’t do an alignment.
  • Polarized the power plug.
  • Added a safety cap from ‘after the power switch’ to B-

After rotating the radio home, and an extended stay playing there, the selenium rectifier gave up it’s ghost, with the accompanying stink. The selenium rectifier was replaced with a modern 1N4007 diode and a series 200 ohm, wire-wound resistor. The modern diode has quite a bit less voltage drop than the old selenium, and the resistor compensates to keep all the internal voltages ‘pretty close’ to what’s on the schematic.


10 thoughts on “Hallicrafters S-120 Gets a Refresh”

  1. My WR 600 has the incoming AC isolated from the chassis. The negative side of the multi-unit electrolytic capacitor is tied to one side of the AC. The S-120 schematic indicates multiple chassis grounds for various circuit connections.

    Should one side of the AC be grounded ?

    1. I don’t think so – if it’s isolated, keep ‘er that way.
      Is the WR600 same (mostly) circuit as the S-120?

      The S-120 *DOES* have one side to chassis. And then they (attempt) to isolate the chassis from
      the outer cabinet – with plastic and fiber washers & such.

      Basically – I don’t think the power plugs on these are polarized. So, you might not be able
      to control WHICH side gets HOT and which side gets Neutral.
      OR – plugs can be wired wrong.

      I do ‘polarize’ the plug, by snipping the side that goes to chassis in the middle. This makes THAT side of
      the plug go to Neutral.
      By ‘snipping’ – I don’t mean ‘cut it off’ – I make a cut (with some wirecutters) in the middle of whichever side
      is connected to chassis. Then I spread it a bit.
      OR – you can do the same by using a modern plug – brown extension cords are great – cut off the ‘extension sockets’,
      and use the polarized cord. WIDE side to the chassis.

      STILL – make sure all the little plastic and / or fiber washers are good and in place, and any plastic feet, since you *still*
      can’t account for mis-wired wall sockets.

      1. Far as I know, the WR-600 (I’m restoring one now) is the same circuit/chassis as the S-120, just in a different cabinet.

        As others have experienced, the electrolytics in the can were bad (nasty power hum), but fairly easy to replace with discrete caps from Mouser or Digi-Key. Still haven’t decided if replacing the paper foil caps is needed yet, as the radio works but seems to not be very sensitive… putting my finger on the ferrite antenna greatly improves the reception.

        The “audio couplate” (brown module with six wires sticking out of it) seemed to be noisy, so I removed that and replaced it with discretes. That helped, but the output is still noisy, so clearly I have some more work to do on it. 🙂

  2. Mike,

    Fascinating write up – thanks for the insight.

    I snagged a used 120 at a thrift store for $8. It does power up, but has a nasty, loud AC hum. Any ideas as to which capacitor to replace?

    Again, thanks for your work on these radio’s.


    1. The large, can-type, capacitor is the culprit. There’s plenty of room under the chassis to put ‘modern’ replacement capacitors.
      Alternatively, Hayseed Hamfest is a website that supplies brand-new replacements for these 3-in-one or 4-in-one capacitors. Specify which model you have (Hallicrafters S-120) and he should have something equivalent.

      1. Hayseed Hamfest is a good outfit – used one of their kits on a S-107 my dad gave to me a couple of years ago. IIRC, they sell entire recapping kits (electrolytic can plus foil caps) or just the can itself.

    2. I have recently acquired a S-120, and it too has a very nasty 60 cycle hum. What this problem usually is, is a bad power supply capacitor (C31, with 3 caps in the can). There are capacitor kits available (Hayseedhamfest.com) that will save you from the order tedium of Digikey. They also tend to have these multi-caps, and as I remember, Digikey has discrete units, which will certainly work, but will not look original.

      Capacitors in electronics basically have three main functions. One is to pass signals between different voltage levels (think plate to grid), the other is to pass AC to ground (think B+ hum filtering) leaving pure DC, the last is as part of a tuned circuit. Note that the value of the first two uses is relatively lax. Larger values and voltage ratings will generally not get you in too much trouble electrically, but size can be a problem.. Tuned circuits not so, the values are generally critical, and you may need to realign to compensate for tolerance. There is a lot to consider with capacitors, including value, voltage, drift, tolerance, microphonics, polarity, dimensions, etc.

      1. Hayseed Hamfest is great. I used them for a Hallicrafters S-100 (Mark I) that I worked on during Summer of 2020.
        Yep, you can get ‘just the can capacitor’, but the recap kit has great quality caps.
        I still need to pull the front off of the S-100 to finish a few around the controls.
        Caps around the tuned circuits are usually mica type and they’ll be verrrry close to their designated value.
        It’s all the paper caps that have dried out. And on the S-120, there’ll be those ‘black beauty’ caps – those are terrible.

        Check resistor values if you can.
        I’ve found occasionally high-value resistors (1 Meg Ω or higher) sometimes those are bad or drift under heat.

  3. Thank you so much for posting the manuals/etc.

    I picked one of these up a few months ago, and it is playing (as-is) in the basement (I am an AM Radio Guy). I am looking forward to being able to fix her up a bit, though it is still working pretty well (albeit it has got some Hum).

    How old is this bad-boy?

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