The Philco 58C from circa 1933/34 is a compact four tube superhet circuit radio often called the "Pee-Wee" or cigar box radio. The cabinet front has a "photo finish" (picture of wood!) making it appear to consist of burl veneer and inlays.
The schematic and a parts list for the radio can be found on Nostalgia Air under Philco model 57. The model 58C uses the same circuit as the model 57 except for an added pilot lamp. Any part number references in the text below reference the model 57 schematic.
My antique radio restoration logs
The radio was purchased on eBay. This is the second example of this radio I have restored. Externally it appeared to be all original, complete and in good condition. It was described as not working, for parts or restoration. The power cord had been cut off. The circuit is quite unusual: it uses a type 77 tube as combined detector/oscillator. There is no IF amplifier stage. A second type 77 tube acts as a regenerative grid leak type second detector. The regeneration adds considerable gain to the stage (and yes, it will squeal if not adjusted correctly). The chassis is quite compact, and servicing is difficult. Access to some components requires partial disassembly. The radio receives the standard broadcast band plus the old police call band - there is no dial scale for this band. According to RadioMuseum.org, the range of the police band is 75-200 meters (1.5-4mHz). There was NO indication of a model number found anywhere on the radio chassis or cabinet. Philco used several variations of this 4-tube chassis in four different cabinets!
I always attempt to avoid purchasing radios that have been "restored" by collectors or flippers, and am looking for either all original examples or those which have been "lightly serviced" in the distant past by radio service shops. Except possibly for tubes, this radio appeared to be all original and untouched:
All resistors were original.
All capacitors were original. All were either Philco bakelite block types or mica capacitors.
The original filter capacitor, along with its cardboard cover, remained in place.
The power cord had been cut off near the chassis exit.
Several tubes likely had been replaced. The originals would have been branded Philco. There were two Philco tubes installed: one with a date code M4 (which may have been original - 1934?) and one with a date code P9 (likely a replacement)
There was no sign of any solder joints having been disturbed.
Before cleaning, the speaker, band switch, filter capacitor, tuning capacitor, and the two bakelite block capacitors on the back of the front panel (parts 10 and 26) were removed. I feared that the air compressor might damage the very fragile speaker cone. Removal of the tuning capacitor was VERY difficult since the retaining screws were hidden BENEATH two transformer shields (for parts 2 and 13). Several parts had to be disconnected from the transformers, the two retaining screws removed, and the two transformer shields moved out of the way in order to remove the three screws and star washers holding the tuning capacitor in place. The dust was then blown off the chassis with an air compressor. The chassis top and sides were cleaned using GoJo (white) hand cleaner and 000 steel wool. The chassis was then carefully vacuumed, and any remaining steel wool fragments removed using a magnetized screwdriver and masking tape.
Before starting repairs I tested all the parts that I could, in case there were any showstoppers.
The power transformer was OK. The AC voltage on both sides of the high voltage center tap was balanced with 20 volts applied to the primary through a Variac. Power consumption at full line voltage with no load was less than 10 watts, which indicated that there were no shorted turns. I always perform this test prior to restoration, even on working radios, since transformer overheating due to shorted turns or other problems may not be obvious with only brief testing. Many collectors new to restoration often completely recap a radio, and even replace resistors and tubes, only to find out they have a bad power transformer after completion.
The primary winding of the antenna coil (part 2) was open. The tuned secondary was OK.
The oscillator coil and IF transformer were OK.
Four dogbone resistors were out of tolerance (more than +/- 20%).
The pilot light was OK.
The speaker field and output transformer were OK.
The grille cloth was torn, and there were tears in the speaker cone.
The power switch on the volume control was intermittent.
The volume control was bad - operation was erratic.
Since all of the original parts were still in place I decided to try to maintain the original chassis appearance to the extent possible yet restore operation. All original capacitors would be rebuilt in their original cases (restuffed), including the original filter capacitor. Any out of tolerance resistors would be replaced with the same types if available. When I replace a component, I always remove the original part completely from a terminal. Other good components connected at the terminal are protected from heat using old medical clamps (hemostats). Excess solder is then removed using a solder sucker in order to expose terminal holes for reattachment of the rebuilt or replaced component.
I assume that all paper and electrolytic capacitors are leaky and thus should be replaced (I always "restuff" the original components if possible). I do not replace mica capacitors, but may test them in place if possible (usually this requires disconnecting one end of the capacitor).
The primary winding of the antenna coil (2) was open. In order to remove the coil for repair, the band switch (8) and associated mica capacitor (5) was disconnected and removed. All connecting leads were then removed from the coil. The coil was held in its shield can by a single hex screw and star washer on the terminal end. It was NOT easy to remove this screw due to access restrictions. I used a small open end wrench (1/4") to remove it. The coil was then manipulated from its shield can (not easy). It would have been easier to disconnect both the antenna coil and oscillator coil connections and then remove both coils and their shields as a unit. But I did not want to risk damage to the coils or disturb lead dress if not needed.
Fortunately, the open winding was on the outside. Also, it was not the tuned winding and thus not critical as to number of turns or wire size. The coil was wound on a plastic insulator on top of the secondary winding. It was covered by wax. As much of the wax was removed as possible using a heat gun. The top end of the coil was unsoldered from its lug. That end passed over the top of the coil. I then attempted to unwind the coil so that the number of turns could be counted. I noted the number of turns, which end went to which terminal, and the winding direction. Since there were several breaks (due to corrosion), my count was only approximate. I counted 22 turns. I rewound the coil using single cotton covered magnet wire which was similar to the original. I then secured the winding in place using melted rosin (salvaged from servicing RCA Radiola Superhet catacombs!)
The original volume control was bad. Its resistance initially measured 43.5K (specification is 20K ohms). The resistance jumped around as the control was rotated. I tried using some cleaner (GC Big Bath spray) but this made things worse! The resistance jumped to 200K! The resistance element in this type of control (C. T. S. Type T) is a thin layer of carbon deposited on a cardboard or fiber substrate. Any attempt to clean it will result in removal of the thin carbon layer. So I had to find a replacement. I keep a stock of new (IRC type D and Q) and used controls of various types. Some of the parameters required are critical in this application:
Must have an attached switch
Since there is a metal shield behind the control, the distance from the panel to the shield (and thus the depth of the control plus its switch) is limited.
The control varies the radio volume by shunting the antenna coil primary winding. So typically a special taper is used in order to obtain smooth control over the entire range of rotation. One type sometimes used is called a "reverse log taper". The change in resistance from minimum volume is fast at first, then decreases as maximum volume is approached. This is just the opposite to the taper typically used for volume controls in modern receivers. The normal alternative is to use a linear taper control. But this results in smooth control over a very small range of rotation.
Must accept a Philco push-on knob, which fits on a round shaft with a shallow flat portion.
I found a similar older type control in my stock that measured about 40K. After cleaning, operation was smooth. The control had an attached switch, which was needed. The shaft length was similar to the original, but was round and not slotted for a Philco push-on knob. The overall depth was acceptable, and there was plenty of clearance between the switch lugs and the metal shield. But the taper of the control was unknown. Although the low resistance hinted that this control may have been used in a similar circuit. This would have to await testing.
The radio used older style "dogbone" type resistors. One was an original cast metal end type and the others were wound end types (lead wires wrapped around the ends of the carbon rod element and then the wraps soldered together). I keep a stock of NOS and used "dogbone" resistors and buy all I can on eBay and at radio swap meets (when reasonably priced)! Of course, most of these resistors, even NOS resistors, have also drifted in value and no longer have their marked values. My solution is to find a replacement resistor of the correct value and size as measured (ignoring the markings), and then repaint it to the needed value codes using enamel hobby paint! I was able to find suitable replacements for three of the four resistors - all 1/2 watt type. In one case I was forced to use a smaller 1/3 watt size dogbone to replace the original 1/2 watt original (part 24). The replacements were repainted using hobby enamel paint to the color codes of the original resistors.
All paper capacitors were Philco bakelite block types. All were removed from the radio (one or two at a time, making careful notes of connections), their contents removed, cases cleaned using lacquer thinner, and restuffed using modern 630 volt film capacitors. Before removing the contents I unsolder the internal capacitor leads from the outside terminals and clean off the terminals. I use mechanical methods of removing the bulk of the potting tar and capacitors (small screwdrivers). One must be careful NOT to pry against the bakelite case, as it is easily broken. Some collectors use heat to remove the contents.
The original filter capacitor was still in place, along with its cardboard cover which simply slips off. The original capacitor was a screw based dual dry electrolytic rated at 8 and 4 mfd at 450 volts (it was marked 12mfd). The terminal lugs were color coded: Black (common negative), Red (8mfd), and Blue (or green) 4mfd. But the wiring of my all original radio did not match the schematics in Riders/Nostalgia Air or the schematics available at Philcoradio.com. These schematics show that the input filter capacitor (connected to the rectifier filament) is 4mfd. In my radio, the input filter was 8mfd (red lug). This could have been an error in the schematic, an assembly error, or a production change. I asked this question on the Philco Phorums, but received no answer. I restored the radio as wired vs. the schematic. It was restuffed with a 10mfd and a 4.7mfd 450 volt electrolytic. There was plenty of room inside the case for these capacitors. The restuffing process for this capacitor was as follows:
The three screws retaining the tuning capacitor are under the antenna and oscillator coil shield cans! The antenna coil already had been removed for repairs. The two hex screws retaining the two coil shields were removed. By disconnecting an 8K resistor (part 8) and mica capacitor from the oscillator coil, the shields could be moved out of the way and the screws retaining the tuning capacitor removed without disconnecting or disturbing other wiring to the oscillator coil.
After removal from the chassis, the tuning capacitor was cleaned in my old Heathkit ultrasonic cleaner using dilute ammonia. Since the entire unit could not be cleaned all at once, several cleaning steps were done, with the capacitor at various angles. After this cleaning and rinsing, the capacitor was cleaned using soap, water, and old toothbrushes. It was then dried using a heat gun. Prior to cleaning the capacitor, the vernier drive assembly was removed for cleaning and lubrication. In addition, the trimmer capacitor screws, washers, and mica insulators were removed. In order to retain the approximate original position of the trimmers, the following procedure was used:
The vernier drive assembly and tuning capacitor ball bearings were lubricated using automotive distributor cam lubricant (grease).
The order of reassembly is critical. After cleaning the chassis and tuning capacitor, the two shielded RF transformers under the chassis were still loose and moveable. The parts were reattached in the following order:
The power cord was replaced by modern reproduction cloth covered wire, and an old style acorn type plug installed. This type of cord is sold for restoration of antique lamps.
The damage to the speaker cone was repaired using GC Service Cement. Each tear or split was bridged using several layers of cement. Each layer was allowed to dry before adding another layer (gently blowing on the cement speeds up the hardening process).
The speaker grille cloth was replaced using a modern reproduction cloth similar to the original.
All of the original tubes were reused, even though several were slightly weak.
The cabinet was in very good shape but with some significant scratches and dings. It was cleaned with GoJo hand cleaner and 00 steel wool.
After the radio was completely reassembled, power was applied through a fused Variac. Power was brought up slowly while monitoring the B+ voltage. The radio came alive and worked on both bands- no assembly errors! The radio was then aligned. Reception on the broadcast band was strong, especially for a 4 tube radio! All I could find on the so called "police" band was weak images of the same stations on the broadcast band and a few strong short wave stations. The design appears to use the second harmonic of the local oscillator for the Police band (the local oscillator frequency range is NOT affected by the band switch). There was noticeable distortion and some speaker cone rattle at higher volume levels, perhaps due the basic design of the radio and damage to the speaker cone.
The replacement volume control worked very well. The range of control was spread out quite well over the range of rotation, and not crowded onto one end. I cut the required flat on the shaft using my Dremel tool.
Most of my restoration objectives were met, but not all. There was no intention of restoring the set to factory new appearance! My objective is usually make the radio appear to have never been repaired. Here are some of my "misses":