|The Zenith model 5S319 (5-S-319) from 1939 is a small tabletop
5-tube AC superhet circuit radio.
It receives the standard broadcast band and one short wave band, and has
"automatic" or push-button tuning.
The radio had seen some servicing and restoration in the past. I decided to try and restore the original top and bottom chassis appearance if possible and reverse previous repairs and restorations to the extent possible.
The schematic for the Zenith 5-S-319 can be found on Nostalgia Air. Any part numbers will refer to numbers on that schematic.
My antique radio restoration logs
A new AC line cord and plug had been installed (the wrong color!)
The original grille cloth and cardboard backer had been replaced (the cardboard backer was likely destroyed when the original grille cloth was replaced). The replacement cardboard looked like it was copied from the original.
The speaker cone had been repaired (a hole patched). Likely someone punched a hole in the cloth and speaker (the reason the cloth was replaced?)
All the tubes were replacements, and most were incorrect: a 6X5GT was installed (should be 6X5G), a 6Y6GT output tube was installed (should be 6K6G), a 6A8GT was installed (should be 6A8G), and a 6R7 (metal tube) was installed and the Zenith gold tube shield removed (should be 6Q7G with shield). A 6K7G was installed, but it was not a Zenith so it likely was not original. All the replacement tubes tested good. The 6R7 and 6Y6GT (which has a 1.2 amp filament!) were not good replacement choices.
The original Zenith filter capacitors had been replaced (one replacement was a 10mfd non-polarized capacitor!)
The pilot lamps were type 1847 (post-war replacement for type 47) and were good.
My usual restoration procedure is to first make a complete survey of the condition of all components. The survey results guide my restoration strategy. If major and unique components are defective or missing and cannot be restored or replaced, I may elect to sell the radio rather than restore it. I always assume that all paper and electrolytic capacitors are leaky and thus should be replaced (I always "restuff" the original containers if possible). Any mica capacitors are assumed OK until testing proves otherwise. The automatic tuning unit (push button assembly) was removed in order to gain access to the other components. Fortunately, only three wires had to be disconnected. I found:
All tubes and shields were removed. The tuning capacitor was then removed for cleaning access to the chassis, and to replace the mounting grommets (I used standard rubber grommets). I then take photos of the chassis bottom so that routing of wiring and component placement can be restored. Lead dress is often critical in radios. When I replace a component, I always remove the original part completely from a terminal. Other components connected at the terminal are protected from heat using old medical clamps. Excess solder is then removed using a solder sucker in order to expose terminal holes for reattachment of the rebuilt or replaced component.
The replacement filter capacitors were removed. The rivet on the side of the chassis which had pulled through a single tie point was removed and replaced with a Zenith type 6-32 hex head screw and nut, which matched other screws on the chassis.
The volume control switch was flooded with Big Bath cleaner and cycled many times. The switch eventually worked. The push-button tuning contacts were badly corroded. The contact springs were cleaned with DeOxit and lacquer thinner. The fixed contacts were eventually cleaned with 600-grit emory paper, followed by lacquer thinner.
The top of the chassis was cleaned with GoJo hand cleaner and 00 steel wool. The tuning capacitor was cleaned in an old Heathkit ultrasonic cleaner with dilute ammonia. After drying, the bearings were lubed with Lithium grease.
The line cord was replaced with a NOS brown vinyl cord (at least it is safe and the correct color).
The grille cloth was replaced with a modern reproduction. The replacement was similar to the original. It was attached to the replacement cardboard backer. The knobs (two of which had chips) were left as is. I was unable to find a source for originals (for split shafts). Reproductions are available, but ALL knobs must be replaced, since otherwise the color will not match.
All paper capacitors were rebuilt in their original cases using modern 630 volt film capacitors in order to maintain the original under-chassis appearance. I reseal the cardboard tubes using rosin salvaged from RCA catacombs (it melts at a low temperature and will not damage the replacement capacitors. The original Zenith filter capacitors had been replaced. I found an original Zenith electrolytic capacitor in my junk capacitor box and fabricated reproduction covers having a similar color, the Zenith logo (found on the web) and the correct original part numbers and values. These covers were then attached to two large tubular paper capacitor cardboard tubes which were gutted and stuffed with new 10mfd 450 volt electrolytics. I was unsuccessful in finding out what the originals looked like, but the reproduction covers look better than just using modern capacitors with no covers (and they do have the correct part numbers).
The one dogbone resistor out of tolerance was replaced by a NOS dogbone resistor that had drifted to near the correct value. It was repainted using hobby paint to the correct color codes. While this resistor may continue to drift, so will the others in the set. I wished to maintain the original above and below chassis appearance.
Once the radio was reassembled and the tubes installed, power was brought up slowly using a variac. AC power consumption was monitored using a watt meter, and a DVM monitored the B+. The radio came alive immediately and worked.
The set was then aligned - no surprises. The push buttons were adjusted to local stations, after I used a signal generator to find the tuning range of each button.
In the BEFORE chassis photo, the push-button tuning unit and tuning capacitor have been removed for access.
Chassis Before Restoration
Chassis After Restoration