The Zenith 6S254 (6-S-254) is a 6-tube console radio with broadcast band and two short wave bands. The radio had been serviced in the past but most of the original parts were still in place. The radio apparently had not been restored (by a collector). I decided to try to reverse any prior servicing and restore the original chassis appearance if possible.
The schematic and a parts list for the radio can be found on Nostalgia Air. Any part number references in the text below reference that schematic.
My antique radio restoration logs
My family owned one of this model Zenith console when I was a child. I fondly remember sitting in front of the radio in our living room listening to the usual old radio shows of the early 1950's. TV did not exist in our city at the time, so this radio along with a portable record player provided the kids entertainment. I was always impressed by the big black dial, large tuning knob with flywheel tuning, copper colored chassis, and the tone.
When TV did arrive in the mid 1950's, the radio wound up in my "shop" (a reclaimed chicken house) in the back yard. I remember listening to what is now called "classic country" music for hours at a time. That radio, like most radios I acquired back then, was eventually destroyed (sigh) for parts. I have looked for another example for years, but shipping was usually an issue and pickup from some distant state required (and no suitable vehicle to transport it). Or else the radio had already been restored. This radio was found on eBay and only 65 miles away, so pickup was reasonable. It had not been restored. It was not a particularly good example, having lots of dings and scratches as well as torn grille cloth (which is unfortunately no longer reproduced). The seller said that the radio made "static sounds", so I assumed that most major components were OK.
The original power cord had been replaced. A rubber grommet had been installed in the hole in the chassis where the cord goes through. I am not sure if this grommet is original.
The grille cloth was torn and a tear in the speaker cone had been repaired. Likely the speaker had been damaged when the grille cloth was torn (penetrated).
Two replacement tubular filter capacitors had been clamp mounted under the chassis. Fortunately, the original filter capacitors were still in place. The original leads to the filters had been spliced and could be restored to their original connections to C18 and C19 once these capacitors were rebuilt.
The dial drive belt had been replaced with a piece of dial cord, which did not work very well (especially since the tuning capacitor was quite gummed up and very dirty). The tuning knob shaft, drive pulley, idler pulley assembly, and flywheel had been removed and reinstalled (incorrectly) for some reason. The front bushing had been removed and reinstalled backward - with the threaded end inside the chassis. This prevented the drive pulley and tuning capacitor pulley from lining up. The rear bushing was also not in place, so that the rear end of the tuning shaft was just flopping around (the bushing was still present on the shaft, fortunately). The idler pulley tension spring was attached to the wrong side, and not attached to the hook designed to hold it. One of the circlips was missing from the tuning shaft, and had been replaced by a piece of solid wire. I have NO idea why all this was done. Perhaps the drive belt was slipping or stiff, but intact, and the shaft was disassembled to remove it or attempt adjustment?
Three paper-wax capacitors had been replaced. Two had been replaced with Zenith parts having the same values but with different Zenith part numbers. These two may have been replaced by a dealer or Zenith authorized service shop.
R6 had been replaced, its failure likely caused by a shorted C6 capacitor (which had also been replaced). There were tell-tale blobs of wax on the chassis mounting board in the general area of C6.
One of the dial glass retainer clips had been removed and the glass secured using Scotch Tape! One dial lamp diffuser had been repaired using Scotch Tape, and the felt ring cushioning the dial glass was broken in several places and had been repaired with glue. It's hard to imagine why a service person would have gone to the trouble of disassembling the dial just to repair a diffuser! The dial pan may have been removed in order to replace the dial drive belt.
Three tubes were branded Zenith and two of those had dates codes containing a "7" (1937?) - the other contained an "11". They may have been originals. The remainder of the tubes were replacements (Sylvania and Philco branded).
After removal of the tuning capacitor, tuning shaft and flywheel, dial assembly and filter capacitors the chassis and remaining top components were cleaned using an air compressor followed by GoJo (white) Hand Cleaner and 00 steel wool, and then toothbrushes and other small brushes. It is critical to keep steel wool far away from a tuning capacitor or tube sockets.
These radios are very easy to service because of the large deep chassis which has lots of space to work. My usual restoration procedure is to make a complete survey of the condition of all components and repair all items before the radio is tested. In this case I did briefly test the radio using a variac and watt meter to make sure the set was really working before providing feedback to the eBay seller. Minimum power was applied for a short amount of time - just long enough to determine that the audio worked (touching the top cap of the 6F5G tube) and static could be heard (touching the antenna terminal).
In Zenith schematics, all resistors and capacitors having the same value have the same part number call out. So for example, there may be multiple R2's or C4's on the schematic. Before I start work on the chassis I annotate the schematic so that all parts have unique identifiers. I usually add an alphabetic suffix, so that the part numbers are thus R1A, R1B, etc. I then annotate the chassis photo with these unique part numbers with a red felt-tip pen. I then removed all non-original capacitors, documenting their locations and connections. 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 power transformer was OK. The high voltage was balanced on each side of the winding's center tap with 20 volts applied to the primary through a variac. It drew less than 10 watts at full line voltage (unloaded), and all filament voltages were correct. I do this test before starting any restoration. A transformer having shorted turns usually shows a significant unbalance (more than a volt or two) across the high voltage and will draw significant power unloaded. It is very sad to read in the various Antique Radio blogs about collectors new to the hobby who will completely recap a radio and even invest in replacement tubes and other parts only to find out after restoration that the power transformer overheats!
The speaker field coil measured open on my DVM, even though the radio worked!
The output transformer measured a high resistance, again, even though the radio worked (or at least made noise)!
The antenna and oscillator coil were OK (tested for resistance and/or continuity).
The IF transformers were OK.
Four original dogbone type resistors were out of tolerance by 30-50%: R3, R4, R9 (6F5 plate resistor) and R5 (6F5 grid resistor). Five original carbon composition type resistors were also out of tolerance.
The wire-wound Candohm resistor R12 was in tolerance and OK.
All the supplied tubes were good and were the correct types (G type).
The volume control and switch were OK.
The rubber chassis washers and tuning capacitor mounting grommets had deteriorated and would have to be replaced.
One of the dial lamp diffusers had a hole burned in it, and the other one was broken and had been repaired using Scotch Tape.
The felt ring which cushions the dial glass was broken in several places.
Both pilot lamps were burned out.
There was a chip out of the top knob (tone control).
Dial drive torsion spring was not attached to the tuning capacitor drive gear. I assume the purpose of this coil spring is to reduce backlash in the mechanism by keeping the reduction gears in mesh at all times.
The dial drive belt had been replaced with a piece of dial cord and the tuning mechanism was not functional.
Since almost all of the original parts were still in place, and since this was going to be a "keeper", I decided to try and restore the original chassis appearance to the extent possible. All original capacitors would be rebuilt in their original cases (restuffed), including the original filter capacitors and the bypass capacitors. Any parts replaced in servicing would be replaced with original parts if available. Any out of tolerance resistors would be replaced with the same types if available.
Both the speaker field and output transformer (mounted on the speaker) measured either OPEN or an unstable high resistance - even though the radio functioned to some extent! I had never seen a failure mode quite like this. Usually, these components are either OK or not. Discussion regarding this issue on Antique Radio Forums concluded that the problem was likely corrosion of the connections between the lead wires and the windings, and that some significant voltage ("wetting current") was required to break through this corrosion. The field coil eventually settled down to the correct resistance. The output transformer never did. As it turns out, I had a similar replacement speaker in stock. This replacement speaker was from a Zenith model 7S342 chairside. It was the same diameter (10") and had the same field coil resistance. The 7S342 and 6S254 use almost identical circuits and both use a 6F6 output tube, so the 7S342 output transformer should work in my radio. However the speaker from the 1939 Zenith was gold colored (vs. 1938 copper colored) and its cable was shorter since it was from a chairside set vs. a console. So it appeared that my choices were:
Use the original 6S254 speaker and replace the output transformer. The issue of course is that the field coil could fail at any time. Also, it was not known if the repaired cone of the original speaker sounded OK.
Have the original 6S254 speaker field coil rewound (and possibly reconed).
Use the replacement 7S342 speaker and replace or extend the cable.
Since I did have a repair strategy, I decided to complete the chassis restoration and test the radio using the original as well as the replacement speaker.
The tuning capacitor was removed from the set, vernier drive gears removed, and then cleaned using my old Heathkit ultrasonic cleaner in dilute clear ammonia. The capacitor would not all fit in the cleaner at once, so several cleanings at different angles were needed. I removed the mica trimmer insulator before cleaning in order to avoid damage. Before removal, I noted the position of the trimmer screw (on the clock) and the number of 1/2 turns to fully tight. By doing this I could return the trimmer to close to its original position after reassembly. After drying with a heat gun, the bearings were lubricated using automotive distributor cam lubricant.
The capacitor mounting grommets were replaced using GPH-46-480 grommets from Renovated Radios. They are not exactly correct, being just a hair too tall, but seemed to work OK. I probably should have removed about 1/32" from the thick side.
The radio uses both older style "dogbone" type resistors as well as carbon composition resistors. Any "dogbone" resistors would be replaced with the same type resistor. 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! In the case of this radio, four "dogbone" resistors had to be replaced: R3 (10K 20% 1 watt), R4 (33K 10% 1 watt), R5 (1 meg 20% 1/4 watt) and R9 (220K 20% 1/4 watt). For R3 I found a NOS 15K 1 watt dogbone resistor in my stock that measured exactly 10K. Thus I only had to repaint the end color black. For the 33K I used a 20K 1 watt dogbone that was close enough (+11%) to 33K and repainted it. The original was solid orange with a silver dot. I repainted the 20K replacement the same way, even though the usual method of marking would be that one END of the resistor would be silver. For R9 (the 6F5 plate resistor) I found a 200K 1/4 watt that was close to 220K. It was repainted as a 220K. For R5 I found a NOS 1 meg 1/4 watt dogbone that measured almost exactly 1 meg..
Five 1/2 watt carbon composition resistors also needed replacement. All of the originals except R7 (390K) were 20% tolerance - R7 was 10%. I did find ONE 20% carbon composition resistor in my stock that was in tolerance. But the remainder were replaced by 10% tolerance resistors (20% carbon composition resistors are no longer available).
The two original can type filter capacitors C18 and C19 (both wet type) were rebuilt in their original cases using new electrolytics. C18, a 16mfd 400 volt capacitor, was restuffed with a 15mfd/450 volt electrolytic. C19, a 20mfd 300 volt capacitor was restuffed with a 22mfd/450 volt electrolytic. My restuffing process for the capacitors is as follows:
Rebuilt Filter Capacitor Cans
All paper capacitors were rebuilt in their original cases using modern 630 volt film capacitors in order to maintain the original under-chassis appearance. The tubular types are easy to restuff. My restuffing process for these types is documented here. The two Zenith capacitors (all labeled C6) that had been replaced with Zenith parts having the same values but different part numbers were replaced with Zenith parts having the correct Zenith part numbers. Why? Because I had the correct parts in stock! These capacitors were restuffed using new axial film capacitors (and one of my objectives was to reverse previous servicing).
Any mica capacitors were tested if one end was disconnected in order to replace another component. C11 (6F5 plate bypass) was rated at 500pf at 600 volts. But it measured only 250pf! It was replaced with a good identical part from my 7S342 parts chassis. All other mica capacitors that I measured were OK.
The end of the coiled tension spring was bent into a hook shape and attached to the existing hole in the tuner drive gear. I am guessing that the original end of the spring broke off in the past. My first attempt also resulted in the end breaking off, so the spring wound up shorter than the original. The tuner still seemed to work OK, and would return on its own after manually moving it to the minimum capacitor condition.
The power cord was replaced using a new brown vinyl cord with molded plug (polarized).
The chassis mounting washers were replaced using CW1 thick chassis washers from Renovated Radios.
I was able to acquire a replacement dial glass retainer clip and screw by posting a wanted advertisement on the Antique Radios Forum Classifieds. It worked OK, but was smaller than the original (perhaps for a smaller diameter dial glass).
I found a large O-ring in my stock that was exactly the right size to replace the dial drive belt. It was found in a bag of large O-rings purchased at Lowes in the department that sells whole-house water filter cartridges.
I found a suitable replacement dial drive circlip in my parts stocks. These and similar parts were salvaged from junk mechanical assemblies such as record turntables and VCRs.
The dial lamp diffusers were repaired using pieces of an old ice cream carton, which was similar in thickness and color to the original parts. The original parts were used as templates and replacements cut out using an Exacto knife with a new #11 blade. The replacements were attached to the originals using GC Service Cement.
The dial glass felt gasket was broken in four places. It was repaired by gluing it to reinforcing material from file folder stock. Strips of material were positioned on the metal dial pan by cutting slots that matched the tabs on the dial pan. Waxed paper was used under the strips of material to prevent them sticking to the dial pan. The broken felt pieces were then glued to the reinforcing strips using the dial pan for alignment of the parts. I used GC Service Cement. Once the glue was dried, any excess material was trimmed flush with the felt ring, and the repair is hardly noticeable. This method produces a much stronger repair than simply gluing the broken butt ends of the felt together.
The 6K7 grid lead (exiting from the first IF transformer) was replaced. The original was very stiff and had a break that was shorting to the transformer shield. The shield had to be removed in order to replace the wire. I sometimes effect this repair by removing the grid cap and installing a piece of spaghetti tubing or heat shrink tubing over the lead.
Both pilot lamps were replaced, but I had only ONE #44 in stock, so I used a #47 for the other lamp.
The cabinet was in good shape but had lots of dings and scratches. It was cleaned with GoJo hand cleaner and 00 steel wool, followed by Old English Scratch Cover (dark) and a coat of Johnson's Paste Wax. The grille cloth (Zenith leaf pattern) was damaged beyond repair and would have to be replaced. Unfortunately, the supplier for most of the antique radio reproduction grille cloth closed up shop, so none is available. Other suppliers are starting to reproduce cloth, and a small number of examples is available. This restoration cannot be completed until the leaf pattern reproduction cloth again becomes available. In the interim, I found a replacement cloth for a later Zenith console on eBay. It was faded on the front side, but usable on the back, and was undamaged. This is what is currently installed.
After the radio was completely reassembled, power was applied through a wattmeter and fused Variac. Power was brought up slowly while monitoring the B+ voltage and the wattmeter. The radio came alive and worked on all bands - no assembly errors! The radio was then aligned. The IF transformers were way off. Other adjustments were close. The volume control was scratchy and was given a couple of shots of GC Big Bath cleaner. It now works OK, but is not perfect. One of the tuning capacitor plates was rubbing at the low end of the dial. The offending plate (antenna section, outside) was bent slightly to fix the problem. This was done before alignment.
The wave trap adjustment did nothing, even though the coil was good. I left it as it was since this function is no longer needed.
The original speaker, with its intermittent resistance measurements and repaired cone, worked perfectly and sounded great.
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 to reverse any prior servicing and make the radio appear to have never been repaired. I do not go so far as to artificially "age" solder joints, as do some collectors! Nothing gives away a restoration faster than bright and shiny solder joints. Here are some of my "misses":