 |
The Zenith 5S228 is a small 5-tube AC tombstone or upright
style radio. It receives the broadcast band and one short wave band. This example had seen extensive servicing or restoration in the past, although not working. I decided to try to reverse any previous repairs and to restore the original above and below chassis appearance to the extent possible. The schematic for the Zenith 5S228 can be found on Nostalgia Air. Any part numbers will refer to numbers on that schematic. |
My antique radio restoration logs
This radio was purchased on eBay. The cabinet was in fair original condition, as were the knobs and grille cloth - lots or wear, dings, scratches and finish loss. There were also fair sized veneer chips on both sides, as well as some cabinet delamination. The radio was sold as not working (occasional static only). In the eBay auction listing, it was obvious that the filter capacitor had been removed, indicating some servicing or restoration. The cord and plug had also been replaced. I always avoid knowingly purchasing a radio that has been restored, as many collectors take shortcuts such as removing the original capacitors and filters. I was hoping that everything except the filter capacitor was original. Once the chassis was removed, my worst fears were realized - every original Zenith paper capacitor, as well as the filter capacitors, had been replaced. All of the original resistors appeared to be in place. Since almost all paper capacitors had been replaced, this was more likely a collector's restoration rather than a service shop repair. Service shop repairs usually result in only a few capacitors replaced. And in this case, all replacements were the same type.
The seller had stated that the chassis was loose in the cabinet. I sent a note prior to payment indicating how the chassis can be secured (10-32 screws and fender washers). Unfortunately, the seller did not take my advice. The packing was VERY POOR - only a single layer of small bubble wrap around the radio, plus crumpled newspaper for padding. The seller did stuff the inside of the radio with newspaper as I suggested. The dial glass was shattered in shipping as a result of the poor packing and failure to secure the chassis. No other damage was found.
The 6Q7G tube had been replaced by a metal 6Q7 and the tube shield had been removed (removal of the shield is often necessary when metal tubes are substituted for G types, since the grid cap lead may not reach the shorter tube with the shield in place). All tubes were replacements. All except one were the correct G types.
All original Zenith paper capacitor had been replaced, all except one by Sprague Black Beauty 600 volt molded film capacitors! That's the bad news. The good news is that guitar fans and audiophools will pay big bucks for certain values of these capacitors on eBay. I will obviously NOT throw any of these away!
The filter capacitor had been removed and tacked in tubular capacitors installed under the chassis.
All resistors looked to be original.
The line cord had been replaced.
The volume control had been replaced. The original was 400K. The replacement was 500K. The shaft type and length was correct for the radio..
One rivet on the 6A8G tube socket had obviously failed and had been replaced by a 4-40 screw and nut.
The antenna coil shield had been removed and only one nut was now holding it in place (the other shield attachment stud was under the band switch and very difficult to access). Also, the antenna lead was routed underneath the shield rather than through the hole in a rivet holding a shield attachment stud. Also there were signs of the wave trap capacitor having been removed and reattached to the top of the shield (which is necessary in order to remove the shield and leave the coil in place).
Several additional washers had been added to one of the tuning capacitor studs. This was likely an unsuccessful attempt at stabilizing the capacitor, since the grommets had deteriorated.
Here is the chassis as received:
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 or unique components are defective or missing and cannot be restored or replaced, I may elect to sell the radio rather than restore it - I am not into "shelf queens". 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. I did not test the radio prior to restoration - I prefer to test all components individually rather than applying power "to see if it works".
Before starting any repairs, I had to determine if the antenna coil (part #2) could be repaired or replaced. If not, it made no sense to restore the radio! The broadcast band primary winding measured open. All other windings were OK. This could have been caused by a nearby lightning strike or contact with an electrical line. The coil shield was removed (with some difficulty) and the coil inspected. One worry: one of the two studs from the shield had no nut! This was the one buried under the band switch. It appeared that someone had removed (or attempted to remove) the shield before. This always worries me! There was no obvious burning, damage or broken wire visible on the coil itself. I then prepared to remove the coil for closer inspection and repair, if possible. There were six connections on the bottom side - so careful notes were taken before disconnection was begun. As luck would have it, the very first lug I disconnected was the ground lug from the cold end of the broadcast band primary winding BUT the bus wire from the chassis ground connection was not connected to the lug! When I measured the broadcast band primary winding from the antenna to the cold end of the winding, it measured 23.3 ohms! For some reason, the connection was compromised and the coil was OK after all!
All tubes and shields were removed. I removed the tacked in filter capacitors. I then took a photo of the chassis bottom so that routing of wiring and component placement could be restored. The replacement capacitors (as well as the original resistors) were identified and a photo annotated with the Zenith part identifiers. In Zenith schematics, all uses of the same part number use the same call out on the schematic. So there may be multiple occurrences of R7 or C6 etc. When I annotate the photo, I add a suffix making each occurrence unique. For example R7A, R7B etc. Lead dress is often critical in radios. Since most of the original capacitors had been replaced, I could not use their locations for reference. Fortunately, I found photos of several chassis that had not be hacked or heavily serviced for reference on-line at Radiomuseum and eBay.
The dust was removed from the chassis using an air compressor. The dial assembly and tuning capacitor were removed. The top of the chassis was cleaned with GoJo hand cleaner and 00 steel wool. This process often leaves behind metal fragments which can cause shorts, so I then went over the chassis with a small magnetic screwdriver to retrieve them. The tuning capacitor (previously removed) was cleaned in an old Heathkit ultrasonic cleaner with dilute ammonia.
All of the replacement capacitors were removed, noting where they were connected. Any remaining original component wiring stubs were then removed from the terminals to confirm the connection points. When I replace a component, I always remove the original part (or wiring stubs left over from past component replacement) completely from a terminal. Other 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.
The Radio Museum photo and other photos found on-line provided some hints as to original component placement. Using the Zenith parts list, I found correct original Zenith paper capacitors to re-stuff in my stock of duds. I collect branded (Zenith, Philco, RCA/GE, etc.) dud paper and filter capacitors just for this situation. These capacitors were rebuilt in their original cases using modern 630 volt film capacitors in order to restore the original under-chassis appearance. I reseal the cardboard tubes using rosin salvaged from servicing RCA Radiola Superheterodyne catacombs (it melts at a low temperature and will not damage the replacement capacitors). Here is how I restuff Zenith tubular capacitors. An AC line to ground capacitor had been installed. That capacitor is not shown in the Zenith schematic in Riders, so it was not replaced.
Most resistors in the set were carbon composition types, and most were 1/2 watt 20% units. Two carbon resistors were not in tolerance and were replaced using the same type resistor, although I was forced to use 10% tolerance resistors. R4, a 33K 10% 1 watt dogbone type resistor, was out of tolerance by about 50%. It was replaced by a 32K 1 watt dogbone resistor I found in my stock that was repainted as a 33K resistor using hobby paints. The 32K resistor measured 34.4K, which is within the 10% tolerance required for this resistor. I collect NOS as well as used dogbone resistors just for this purpose, and buy all I can find on eBay and at swap meets (at reasonable prices).
The Candohm wire wound resistor was in tolerance, and its resistances were stable when terminals were moved. Its resistances are not documented on the schematic. However a Google search found the resistance values in an Antique Radio Forums topic.
The original filter capacitor can had been removed. I had a replacement can in my stock, but it was not in very good shape. It was damaged in the process of attempting to remove the original contents. After heating the case, the contents would not budge. I had to resort to removing most of the contents using a 1" spade bit in my small drill press. The balance was removed using screwdrivers and other instruments (this is what damaged the metal case). The original values were 8mfd and 14mfd at 450 volts. I rebuilt it using two 4.7mfd 450 volt capacitors and a 15mfd 450 volt capacitors. New wire leads were added, and the capacitors were wrapped in strips of paper towels to hold them in place. The capacitor was then sealed using RCA catacomb rosin.
A 6Q7G tube replaced the metal 6Q7, and a Zenith tube shield added (1938 color was used). The remainder of the original tubes were reused (all were good).
The tuning capacitor mounting grommets were replaced by standard 5/16" vinyl grommets. The dial drive cable (a piece of string as found) was replaced using standard black dial cable. The existing spring and eyelets were reused. The original gimmick capacitor on the tuning capacitor was nothing but bare wire as found (likely originally rubber covered). It was replaced by a piece of solid insulated wire that was wrapped around the 6A8G grid lead in the normal fashion.
The deteriorated spaghetti tubing covering the tone control wiring shield was replaced by heat shrink tubing.
Splits and holes in the speaker cone were stabilized using GC Service Cement. A large hole was patched using black paper from a donor speaker I keep around just for this purpose.
The pilot lamps were replaced using #47 bulbs. The diffusers were repaired by attaching pieces of plastic salvaged from an old ice cream carton, which is close to the correct color. Not perfect, but it works. It was attached toe the existing diffusers using super glue.
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 with only 70 volts AC applied. It worked on both broadcast and on short wave. I noticed that on short wave, at quiet places on the dial, and the band/tone switch in the treble position, a squeal would occur if the volume control was advanced to the maximum. This could be due to altered lead dress or routing. However, it is not an issue since one would not normally do this. The B+ measured 265 volts with only 110 volts applied (specification is 246 volts at 117 volts input). This may have been due to my using a 10mfd input filter vs. the original 8mfd.
The set was then aligned. There were no difficulties. The IF adjustments were way off. The broadcast band antenna trimmer could not be peaked - the signal was still increasing at minimum capacity.
The set has excellent sensitivity for a 5-tube set, especially on the broadcast band. Unfortunately, there was some rattle in the speaker at higher volume levels with the treble cut and the speaker out of the cabinet. Not much I could do about this except finding a replacement speaker or re-coning the existing speaker. The performance was OK with the speaker mounted in the cabinet.
|
Chassis Before Restoration |
Chassis After Restoration |
|
 |
