Another in the S-38 Series from 1957-1961 era

I purchased the old radio for $30 from Jim Heye (K5WLQ). I never plugged it in, respecting the fragility of possible old paper and electrolytic capacitors, but the first thing I noticed was that the main tuning dial was strung backwards! The cabinet was nice, with a few nicks and scratches from a normal life — not as nice as I would have liked, but cleanable. The S-38E is the grey hammertone finish; it was also available in S-38EB (beige) and S-38EM (mahogany). It’s a swell example of the era, with the short (pre-1970’s) AM dial and the CD — Civil Defense — marks at 640 khz and 1240 khz.

This radio was clean inside and required the least amount of work, other than a dial restringing, capacitor replacements and safety rewiring. This particular unit is a ‘Mark II’ model, with the adjustable CW setting on the back. This adjustment can be used to improve the clarity of CW reception. In previous models this was a fixed setting by use of a ‘gimmick’ capacitor.

The S-38 Series was introduced in 1946 (S-38) and were produced through 1961 (S-38E). The S-38E
was produced from 1957 to 1961, making it the end of the line, priced at about $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-38E, all 9-pin ‘miniature’ tubes — a departure from the older octals:

• V1 – 12BE6 Mixer / Oscillator
• V2 – 12BA6 IF / CW BFO
• V3 – 12AV6 Detector / Audio Amp
• V4 – 50C5 Audio Output
• V5 – 35W4 Rectifier

Left to right: Antenna lugs A1, A2, Ground lug (soldered directly to the chassis!), cw adjustment (Mark II model only), phone output.
Note the use of miniature tubes. Serial number looks to be: 252816, with an over stamped Q42301. Not shown, to the right, the power cord is permanently attached.

Wiring Safety

The S-38E is a transformer-less radio, and like the S-38B, presents quite dangerous shock hazards.
At some point, however, an attempt was made to isolate B- from the chassis a bit, and to provide for some safety by bridging the B- (ground) and the metal chassis with a 470k ohm resistor in parallel with a 0.06 micro-farad capacitor. However this doesn’t completely remove 120VAC from the chassis or the antenna ground-lug, which is soldered directly to the chassis.

For safety, the switch, which is designed to connect one wire of incoming power directly to the B-, is moved to the other leg, and the newly polarized plug’s ‘neutral’ is placed at the point where the last filament is joined to B-. This assures that (provided the electrical socket is wired properly) the chassis, antenna ground-lug and B- are close to ground.

Moving the switch away from B- and polarizing the plug makes the radio safe.

The power cord is attached to the radio. After a safety rewire, 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. I’ve received 40m CW and
11m CB. AM Broadcast is strong and clear.

Radio is tuneable from 540KHz to 32MHz across 4 switched bands:
• Band 1 (AM Broadcast) 0.540 – 1.65MHz
• Band 2 1.65 – 5.1 MHz
• Band 3 5.0 – 14.5 MHz
• Band 4 13 – 31.0 MHz

Completed Appearance Improvements

• Cleaned the cabinet, dials, and knobs.
• Replaced some missing cabinet (back and bottom) screws.
• Finally bought some Bristol Keys to properly remove the knobs.

Always use Bristol Keys (McMaster-Carr #7048A55) to take the knobs off. Hex keys will occasionally ‘work’ to get the knobs off, but they will always destroy the little slug that holds the knob.

Completed Repair Items

• Cleaned the Band Switch, the front-panel switches and Volume Control with De-oxit
• Replaced the multi-stage Electrolytic with a terminal strip and 4 separate electrolytics
• Replaced all the tubular capacitors.
• Rewired the power connection and polarized the power plug for Safety.

(corrected:) No capacitors have been changed here yet. Original 4-in-1 electrolytic to the left; trimmers center and right.

Resources

Clean scans of schematics are not available via internet, as far as I can find. The usual sources list the user and service manuals, but in some cases only for the ‘non-Mark II’ version. The available Mark II version schematic is a poor scan, in some places illegible. I replaced a tiny mica cap, C16 and if it had been missing or in bad shape, I’d not been able to read its value: 82pf. I plan to take a trip to the Dallas Library Sams Photofacts section for this and a few other scans.

• S-38E Mk II Schematic
• Service and Owners Manual
• A must buy for this and other S-38 series radios is a 10-piece Bristol L-Key Set (McMaster-Carr #7048A55).
  These can be found on eBay for around $21 (plus shipping), but McMaster-Carr has the same set for $15.50 (as of Jan 2009)

Status

The S-38E was given to a local gentleman who had contacted the W5FC Club and wanted to try some Shortwave Listening (SWL). I donated the S-38E to the cause, although antenna issues in his location limits his reception. http://www.websdr.org/ fixed that and he is now happliy listening in on CW QSOs all over.

Fortunately an identical S-38E recently replaced it, an almost pristine MKII model, which only required fresh electrolytics and power cord rewiring.