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Hallicrafters S-120 Restoration

Discussion in '"Boat Anchor" & Classic Equipment' started by WD5HHH, Nov 17, 2015.

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  1. WD5HHH

    WD5HHH Ham Member QRZ Page

    I was given an S-120 that is supposedly non-operating. After some research it appears that it is a variant on the All-American 5 tube with a selenium rectifier instead of the tube rectifier.

    I will try bringing it up with my variable transformer and see if it works. Even if it works, I am probably going to replace the rectifier with a modern silicon diode and resistor. I suspect the filter caps are bad since it is nearly 50 years old. I have found suggestions to replace with 200+ volt capacitors. The values appear from the schematics I have found (copies) to be 60-40-40. I am having trouble finding a source for these. Any suggestions? I tried the Fry's that is about 30 miles from here and they didn't have any parts that would suffice and with the demise of Radio Shack stores in my area which might have had the rectifier and resistor, I want to order all parts at the same time.
  2. W7UUU

    W7UUU Super Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

  3. WW3QB

    WW3QB Ham Member QRZ Page

  4. W5RKL

    W5RKL Ham Member QRZ Page

    My recommendation is to replace the original 2 blade power plug with a 2 blade polarized plug.

    The picture below show the S120 AC plug wiring. Both blades on the original power plug are the same size which can, if inserted into the wall outlet one way, apply AC voltage to the S120 chassis.


    A polarized plug has 2 blades, one blade is wider than the other and can only be inserted into the 120VAC wall outlet one way.

    The "Wide" blade connects to the S120 chassis ground and the end of the tube filament and dial lamp string as seen in the picture above.
    The "Narrow" blade connects to the front panel ON/OFF switch as shown above.

    Wiring the polarized plug this way will always put the S120 chassis at ground.

    If you look at your 120VAC wall outlet you will notice the Left vertical opening is taller than the Right opening.
    The Left opening corresponds to the polarized "wider" blade, AC Neutral and the "right" smaller opening corresponds to the "narrow" blade "AC Hot".

    Mike W5RKL
  5. WD5HHH

    WD5HHH Ham Member QRZ Page

    Thank you all. The Hayseed Hamfest re-cap kit is not much more expensive than the total cost of just the filter capacitors from Mouser or Digikey and looks like a reasonable buy. Mike, I was going to rewire for a polarized plug. I think that I will also add a fuse in the power circuit as a precaution. That is not per the design but I believe a good addition.

    Bill, WD5HHH
    Last edited: Nov 18, 2015
  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    I definitely would use a 3-wire cord and connect the green wire to the cabinet. Wire the black wire through a fuse and then to the off/on switch. The white wire needs to go to the "other" side of the original AC cord.

    This is how I wire any unit that comes in for restoration. I absolutely refuse to let anything go out with a 2-wire cord!

    Make sure that the cabinet is isolated from either side of the original 2-wire cord. The insulating washers, that are between the cabinet and the chassis, may have gone bad over the years.

    I need to look at my S-120 and see just how things are actually wired.

    Glen, K9STH
  7. W5RKL

    W5RKL Ham Member QRZ Page

    Most hose wiring today has the AC Main "NEUTRAL" wire connected directly to the breaker panel's metal enclosure. This allows mixing of the AC Neutral WHITE wire and the Safety ground bare copper wire on the same ground bus bars.

    I agree, a fuse holder should be added to the S120 primary power wiring between the AC Hot and the ON/OFF switch. The S120 at 120VAC/DC dissipates 30 watts which equates to an approximate current level of 250ma.


    The above partial schematic was cut and pasted from the original factory supplied S120 schematic in the user manual. As one can see, the AC power plug is a 2 blade plug, one blade connects to the ON/OFF switch and the other blade connects to the S120 chassis.

    The original 2 blade plug, both blades are the same size, allows the original power plug to be inserted into the wall outlet 2 ways.

    1. Plugging the power plug into the wall outlet one way places 120VAC on the S120 chassis (AC Hot at the S120 chassis ground) and AC Neutral connected to the ON/OFF switch.

    2. Turn the plug around 180 degrees and plugging the power plug into the wall outlet places the S120 chassis at ground potential through the house AC Neutral wire, same ground potential as the AC Neutral wire and Safety ground bare copper wire is back at the house breaker panel and AC Hot to the ON/OFF switch.

    A 2 blade polarized plug has 2 blades, one blade is wider than the other, allows the plug to be inserted/plugged into the wall outlet only one way. The polarized plug is connected to the S120 as follows:

    The Narrow blade connects to one terminal of the newly added fuse holder.
    The Wide blade connects to the S120 chassis, same as the original power plug connection as shown in the S120 partial schematic diagram above.

    Today's wall outlets have 3 openings, 2 vertical openings one is wider/taller (Left opening) than the other, and a round opening. One will notice the "Left" opening is "taller" than the "Right" opening. This allows for the use of a 2 blade polarized plug where teh WIDER blade on the polarized plug inserts into the LEFT opening and the Narrow blade of the polarized plug inserts into the "RIGHT opening. The Left opening is AC Neutral, the Right opening is AC hot, and the Round opening is the Safety Ground.

    A 3 wire power cord can be used, the WHITE wire connected to the S120 chassis, the BLACK wire to one terminal of the fuse holder, and if desired, the GREEN wire connected to the S120 chassis. Connecting the GREEN wire to the S120 chassis is a redundant ground as it is the same ground as the AC Neutral is, back at the house breaker panel.

    Mike W5RKL
    Last edited: Nov 20, 2015
  8. W9GB

    W9GB Ham Member QRZ Page

    Hallicrafters S-120 SW Receiver
    Production year 1961 - 1964 at $69.95

    The Hallicrafters S-120 is a single conversion, superheterodyne, general coverage receiver that is used for the reception of AM and CW signals. The S-120 turned out to be a very popular receiver for the Hallicrafters company and was the successor to their famous S-38 line. The receiver incorporates four tubes and a selenium rectifier in its circuit.
    The S-120 has a total of four bands with continuous coverage from 540 KHz to 31 MHz.
    The first band covers 540 KC to 1600 KC, the second band covers from 1.6 MHz to 4.4 MHz, the third band covers from 4.4 MHz to 11.5 MHz, and the fourth band covers from 10 MHz all the way up to 31 MHz.
    The analog slide-rule frequency display has been imprinted with a guide to the frequency settings for foreign, WWV, government, aviation, and other exotic stations.

    John Fuhring (Santa Maria, CA) has High Resolution scans of the Hallicrafters S-120 SW receiver.

    John's restoration article (above) covers:
    1. Capacitor replacement
    2. Construct an actual 455 kHz BFO (using a modern FET and modern 455 kHz IF can)
    3. Silver Mica disease with IF cans
    4. Rewiring AC (line voltage) for safer operation
    There are YouTube videos of various people attempting radio repairs (like the S-120).
    BTW, Mike, W5RKL had some nice videos.
    The Antique Radios Forum is also a good resource -- with a number of SW radio restorers.

    IMHO, some YouTube DIY presenters have "poor bench skills", and obviously were self-taught without experience of a good electronics Elmer (master/apprentice/Padawan learner/novice).
    My Elmers stressed the importance of clean work good soldering, and lead dressing -- in other words "your work / repairs should be indistinguishable from factory hand assembly".

    This gentleman would get a "C" in my high school shop classes.
    While the S-120 works, the craftsmanship of repairs / capacitor replacements is below average (poor).
    Craftsmanship requires skill, proper tools, time, and attention to details --
    just like any Old World materials Craft (Wood, Metal, Glass, Fabric, and Stone).

    Part 2
    Last edited: Nov 20, 2015
  9. W5RKL

    W5RKL Ham Member QRZ Page

    I had an S120 back in the late 60s. Didn't have much time to play with it since I was in the Navy and stationed aboard a destroyer, USS GURKE DD783, out of San Diego, Calif as a Radioman. I had R390s, WRR2s, and R1051s to mess with so I left the S120 at home in Cincinnati, Ohio. I have considered picking up another S120 to play with.

    Mike W5RKL
  10. W5RKL

    W5RKL Ham Member QRZ Page

    I built a small 456Khz BFO circuit using a 455Khz resonator I picked up on eBay to replace a failed 456Khz LSB BFO crystal in my Allied SX-190 receiver.

    I have a video of the 456Khz BFO on the self powered breadboard feeding the SX-190 in LSB during final testing:

    I also have a picture showing the same 456Khz BFO circuit that was moved from the breadboard to a small Radio Shack perf board:

    A new 456Khz crystal would have cost over $50.

    A few inexpensive components, a small cheap Radio Shack perf board, was significantly cheaper than $50+ for a new replacement 456Khz BFO crystal.

    I do not know if my 455Khz BFO circuit I built will work in the S120 or not.

    Mike W5RKL

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