Hallicrafters S-38B Refurb

An Old Radio Becomes New Again - 60 Years Later.

I purchased the old radio for $30 from a W5FC club sale of some old gear. The radio worked only (barely) on the AM broadcast band. A couple of wires had been soldered to the top of the main tuning capacitor, which indicates that probably, in a previous life, the radio had been a part of a transmitter/receiver combo. A small hole is in the right-rear side of the cabinet, etched EW / NS - possibly an antenna hack.

S-38B Refurb

This little radio spent some time in regular use at my office after the initial capacitor replacements and safety rewiring.

The S-38 Series was introduced in 1946 (S-38) and were produced through 1961 (S-38E). The S-38B was produced from 1947 to 1952 and sold for about $49.50. Internally, the radio is a classic "All-American 5", which makes it very easy to work on. The original S-38 has 6 tubes, but subsequent models have 5.

    Tube Lineup for the S-38B
  • V1 - 12SA7 Mixer / Oscillator
  • V2 - 12SK7 IF / CW BFO
  • V3 - 12SQ7 Detector / Audio Amp
  • V4 - 50L6GT Audio Output
  • V5 - 35Z5GT Rectifier

The S-38B is a transformerless radio, presenting quite dangerous shock hazards. When working on the radio, an isolation transformer should be used. But the safety of the radio also relies upon 4 tiny chassis-cabinet insulators for the safety of the user. Should the internal chassis connect with the outer cabinet, a shock hazard would be present. In this case, if the original plug is not polarized, and depending on which direction it was plugged into the electrical socket, one of two conditions would be present:

  • Hot is connected to the switch, such that turning the radio ON applies AC to the chassis ground and makes the chassis hot.
  • Neutral is connected to the switch, such that the chassis is hot all the time; touching the hot chassis to ground could actually turn the radio on without the switch.
S-38B Refurb - AC Safety Rewire

Polarizing the plug makes the radio safe.

Fortunately, the S-38B incorporates a cord-lock mechanism into the back panel. With the back panel in place, the cord can only be installed one way. Polarizing the cord assures that the hot leg always is sent to the switch and the chassis-ground is tied to neutral.

Current Status

This little radio is now receiving on all bands except possibly the lower half of Band 4 (13.5 to 31 mega-cycles — could just be no activity in that band). Still experimenting with this band a bit. In later S-38 series (C and D) the 470,000 ohm resistor (R1) in parallel with the 2700pf capacitor (C6) is dropped, so I may have to try this as an option (this didn't work). Band 4 is extremely weak, although it aligns properly, per service manual. All other bands are very strong; I listened to a SSB conversation on 160m for a long time and was able to tune others on 80m and 40m, including CW.

    Radio is tuneable from 540KHz to 32MHz across 4 switched bands
  • Band 1 (AM Broadcast) 0.540 - 1.65MHz
  • Band 2 1.65 - 5.0 MHz
  • Band 3 5.0 - 14.5 MHz
  • Band 4 14.5 - 32.0 MHz

Completed Appearance Improvements
  • Cleaned the cabinet and dials.
  • Replaced some missing cabinet screws.
  • Removed the extra wires soldered to the main tuning capacitor
Completed Repair Items
  • Replaced the burned out Type 47 Dial Lamp.
  • Cleaned the Band Switch and Volume Control with De-oxit
  • Replaced the multi-stage Electrolytic with a terminal strip and 4 separate electrolytics
  • Replaced all the tubular capacitors.
  • Replaced the line cap with a modern X1/Y2 safety cap.
  • Rewired the power connection and polarized the power plug for Safety.
Final Completed Items - December 2008
  • Replaced the 6 mica capacitors and a couple of out-of-tolerance resistors.
  • Performed a full alignment, according to the Rider's Service Guide.
  • Reception is extremely strong on Bands 1 to 3; Band 4 is weak
I wish I had about 4 more of this series to redo; they're fun to work on.

S-38B Underside

All except the mica caps have been replaced here; also AC "hot" leg goes directly to the On-Switch.