|The Zenith model 6S322 (6-S-322) "Stars and
Stripes" from 1939 is a tabletop
6-tube AC superhet circuit radio.
It receives the standard broadcast band and two short wave bands, and has
"automatic" or push-button tuning. This radio also
featured flywheel tuning, which is rare except in "deep chassis"
The radio had seen minimal servicing in the past. I decided to reverse previous repairs to the extent possible.
The schematic for the Zenith 6S322 Chassis 5651 can be found on Nostalgia Air. Any part numbers mentioned will refer to numbers on that schematic.
My antique radio restoration logs
All tubes and shields were removed.
Dust was blown off using an air compressor
I then took "before" photos of the chassis so that routing of wiring and component placement can be restored. Lead dress is often critical in radios.
The dial assembly, dial drive cable and dial pointer were removed.
The tuning capacitor was then removed in order to renew the mounting grommets and for cleaning and lubrication.
A replacement AC line cord and plug had been installed (white)
Two tubular type replacement filter capacitors for C20 and C21 had been installed (similar type to the originals, but not clamp mounted).
One original Zenith wax paper capacitor had been replaced - C15. The remainder were all original.
All resistors were original.
The original Zenith first IF transformer had been replaced by a newer, smaller unit.
Some of the tubes may have been replaced. The 6F5G, 6F6G, and 6K7G were Zenith branded, and likely original. The remainder were Tung-Sol branded. I assume that these were replacements, since it is my understanding that Zenith radios were originally shipped with Zenith branded tubes. All the tubes were the correct G types.
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. I found:
Before starting repairs, I had to deal with the replacement first IF transformer and the open antenna coil. If these parts could not be replaced with Zenith originals, I may have elected not to keep the radio and wait for a better example. The antenna coil was removed from the radio and the coil removed from the shield can. The damage was obvious. The broadcast primary winding (bank wound) was completely loose in the can, and showed signs of burning. The wax that normally retained the coil in place had melted. So apparently some voltage had been fed into the antenna. Perhaps the antenna fell on a power line. The damage did not appear to have been caused by lightning, since it took some time for the wax to melt. The short wave primary coil (in series with the broadcast band coil) amazingly was not damaged. My choices were thus:
I did have a Zenith parts chassis, model 6S342 in stock. That radio had identical band coverage, the same converter tube (6A8), and the same number of plates on the tuning capacitor. But the part number was not the same as in the 6S322. I removed the coil from the parts chassis and examined it. It looked identical. So I decided to replace my defective coil from the parts chassis and see how well it worked. If it did not work, I would then try to rewind the primary coil or find a part chassis.
The first IF transformer on the 6S342 parts chassis looked correct for my chassis - it had the same mounting centers as well as the 6K7G grid cap lead. The 6S342 used the same converter (6A8) and IF amplifier (6K7) tubes, and the IF frequency was the same on both radios. But again, the part numbers were not the same. The DC coil resistances were slightly different (comparing the replacement transformer primary resistance with the original second IF transformer primary resistance). So I decided to install the replacement from the 6S342 parts chassis and see how well it worked after alignment.
The 6S342 parts chassis also provided the missing pin plug for the lead going to the automatic tuning unit. But alas, the 6S342 automatic tuning unit could not provide a replacement for the damaged coil and adjustment screw I needed.
So having a strategy for replacing the missing original parts, I decided to proceed with the restoration.
The top of the chassis and remaining top chassis parts were then cleaned with GoJo hand cleaner and 00 steel wool. After cleaning, the chassis is carefully inspected for steel wool fragments. It is important to keep steel wool away from the tuning capacitor (it had already been removed). The tuning capacitor was cleaned in my old Heathkit ultrasonic cleaner, followed by soap, water, and toothbrushes. The unit was then dried and bearings lubricated using distributor cam lubricant (similar to the original grease used).
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 automatic tuning contact springs and contacts were cleaned with lacquer thinner on a pipe cleaner followed by DeOxit and then more lacquer thinner and a pipe cleaner. But corrosion remained. So I then used a Dremel tool with a wire brush attachment to clean the contacts and contact springs as well as possible. The fourth spring had been repaired by soldering. I was never able to get reliable contact between that spring and the contacts - the contact springs are almost impossible to adjust due to restricted access. The coil and adjustment for the fifth button had been destroyed when the adjustment screw (or slug) seized up and was broken off. So I wound up with only 3 automatic tuning buttons that worked.
Seven original resistors were out of tolerance. One was a dogbone type (R4, 33K, 1 watt). The remainder were normal 1/2 watt carbon composition types. For R4, I found an NOS 33K 1 watt dogbone resistor in my growing stock of dogbone resistors. It measured 29.54K. The 1/2 watt carbon composition resistors were replaced using similar 1/2 watt carbon resistors. Most originals were 20%, while most replacements were 10% or 5% units, but were otherwise similar in appearance.
The non-original capacitor C15 (part 22-435, .02mfd, 600 volts) was replaced using an original dud from my stocks. It was restuffed using a .022mfd 630 volt film capacitor. I have an ever growing collection of original branded (Zenith, Philco, RCA/GE, Atwater Kent etc.) wax-paper capacitors for just this situation. All original Zenith paper capacitors remaining were rebuilt in their original cases using modern 630 volt axial film capacitors in order to maintain the original under-chassis appearance. I reseal the cardboard tubes using rosin salvaged from RCA catacombs. This material is a mixture of rosin, beeswax, and other material which melts at a low temperature and will not damage the replacement capacitors.
Both original Zenith filter capacitors C20 (22-718, 12mfd, 450 volts) and C21 (22-719, 16mfd, 350 volts) had been replaced. Remnants of their original clamps were found in the radio. In a previous restoration, I had used an original Zenith 22-719 cardboard case, restuffed. This part originally came from the same Zenith 7S-342 parts chassis mentioned before! I had photographed it for future reference. I found two dud clamp mount electrolytics in my junk capacitor stock that were about the correct size. I then fabricated paper labels for them indicating the Zenith logo, part numbers, and values. The paper labels were split to clear the clamp and attached with service cement. For C20, I used a 10mfd/450 volt capacitor (since this was the input filter capacitor, and line voltages are higher today). For C21, I used a 22mfd/450 volt capacitor to partly compensate for the lower input capacitor value.
|An original filter capacitor C21
Part 22-219C, 16mfd/350 volts
|Reproduction capacitor for C20.
Installed in the radio. I could not
get the color correct in Word.
I do not install the automatic tuning unit until the radio is working and aligned. 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 B+ was high at 115 volts input (267 volts vs. a spec of 230 volts), even though the input filter capacitor was 10mfd vs. the original 12mfd. The bias voltages were also higher than specification. I lowered the AC input voltage until the B+ measured at the 6F6 screen was the correct 230 volts. At that voltage, the bias voltages were still high. This was likely due to all sections of the Candohm resistor R12 measuring slightly high (but within tolerance). However, the radio worked well and sounded great! There was some modulation hum on station, but this went away when a ground connection was made. I had this same problem in another similar restoration of a Zenith 6B321.
The set was then aligned. The replacement first IF transformer, as well as the replacement antenna coil peaked up nicely.
The three push buttons that were operative were adjusted to local stations.
Chassis Before Restoration
Chassis After Restoration