Zenith 216-2 Zenette Restoration

The USA stock market crash of 1929 and the following Great Depression resulted in a market mismatch with Zenith's early 1930's line of expensive radios. So Zenith developed a low cost product line in order to better match market needs. In order to distinguish those radios from their high-end line, they branded them "Zenette" rather than Zenith.  Although supposedly a low-end radio, the build quality of my radio is very high. The Zenith Model 216-2 Zenette is the more rare 25-30Hz model.  These radios were only used in the Niagara Falls area of New York and Canada, where 25hz AC power was being produced. The circuit is a conventional 7-tube superheterodyne that receives only the broadcast band. It features a tuned RF amplifier and separate oscillator and mixer stages.  It uses 2.5 volt tubes, typical of the early 1930's. The radio had seen some servicing in the past but had not been hacked excessively.  This being the case, I decided to try and retain the original top and bottom chassis appearance if possible.  The schematic and parts list for the radio can be found on Radio Museum (Nostalgia Air/Riders has only the schematic).

My antique radio restoration logs

Survey

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 and cannot be restored or replaced, I may elect to sell the radio rather than restore it.  I assume that all paper and electrolytic capacitors are leaky and thus should be replaced (I always "restuff" the original components if possible).  And most original resistors would have drifted and be out of tolerance range.

• A type 5Z3 tube had been installed to replace an 80 (yikes - hopefully no power transformer damage!)

• A type 2A6 tube had been installed to replace a type 55 (not a good match).

• The type 59 output tube was VERY weak.

• The original filter capacitor block had been replaced by two Aerovox 8mfd box-type capacitors inside the original metal cover.  One of these capacitors had been replaced by a tubular filter under the chassis (obviously a second repair).

• All of the original paper-wax capacitors and dogbone type resistors were still in place.

• The power transformer was OK.  It was a 25-30Hz transformer, but had an optional capacitor across the speaker field coil marked as "60 cycles only" in the schematic, so I assumed it would work on 60Hz.  I tested it on 60hz with a watt meter and a variac. It drew almost no power (5 watts or so) unloaded at 120 volts input. All output voltages were correct,  and the high-voltage winding was balanced on each side of the center tap.

• The speaker field and output transformer were OK.

• All RF coils and transformers were OK.

• The original power cord was usable - it had only one bad spot about 1' from the plug.

• The power switch on the volume control was defective but likely needed only cleaning (the dreaded BradleyStat type control).  The volume control itself also needed cleaning.

• The tone control potentiometer was intermittent and needed cleaning (another BradleyStat).

• Almost all original dogbone type resistors were out of tolerance by 30-100%.

• One speaker socket terminal was broken loose from its mounting (this was left in place, since there was no obvious way to repair it, and it worked OK once the speaker lead connector was attached).

• The two Candohm type (metal cased) power resistors were both OK, fortunately.  

Cleaning

I normally clean the chassis before starting restoration.  I first blew off the above and below chassis dust with an air compressor.  The chassis was then partially disassembled for access and cleaning.  The tuning capacitor and dial drive mechanism was removed as a unit after unsoldering the leads and ground braids.  I had to remove the mixer coil shield cover in order to gain access to the screws and spacers that held tuning capacitor shield to chassis.  The filter capacitor block cover was removed.  The volume and tone controls and their bracket  were then removed after disconnecting all wiring from the controls.  It was very difficult to manipulate the controls and bracket out of the chassis - there was no room to remove the controls before removing the bracket, and the bracket could not be removed without first removing the controls!  So I had to loosen the control nuts, leave the controls in place, and bend the bracket slightly in order to remove it.

The chassis and top components were cleaned using GoJo, steel wool, and toothbrushes.  The tuning capacitor was removed from its shield cover and cleaned with soap, water, and toothbrushes and then dried using a heat gun and lubricated.  The complex brass helical ring-and-pinion gear dial drive mechanism was removed, disassembled, cleaned, and lubricated.

Repairs

All paper capacitors (13) were rebuilt in their original cases using modern 630 volt film capacitors in order to maintain the original under-chassis appearance.  The radio used Dubilier Cub type capacitors, which are difficult to restuff.  My process for restuffing Cub capacitors is documented here.

All the Cub capacitors were originally marked with paint: either ORANGE (for .1mfd), YELLOW (for .05mfd), or GREEN (for .25mfd).  Cleaning the cardboard case removed most of the paint, so it was replaced after rebuilding.  I suppose this was to simplify assembly, since the person assembling the radio would not have to read the label on the part!

Main Filter Capacitor Block Replacement

I fabricated a replacement main filter block using two 10mfd/450 volt tubular electrolytic capacitors.  The original block was two 8mfd/500 volt capacitors.  There was evidence remaining that the original capacitor block had terminal lugs (there were remains on some of the wiring).

• Cut a piece of insulation material (Fish Paper) to the pattern of the base of the outer metal capacitor cover (so it would be largely hidden when the cover is in place).
• Cut a piece of hard rubber (1/8" thick) to fit inside the outer metal cover (you could also use 1/8" or 1/4" plywood)
• Sandwiched these two items together and drilled 4 holes at the corners for 6-32 hardware, spaced so that the ground lugs would not contact the chassis or metal cover..
• Installed 4 ground lugs above and below, screwed together with 6-32 screws and nuts
• Installed 2 10uf 450 volt tubular caps on the top side, connected to the ground lugs
• Reattached the cover to the chassis.  The retaining screws passed through the Fish Paper thus holding the components in place.  
• Reconnected the original wiring to the bottom ground lugs

Dogbone Resistor Replacement

All original resistors more than 20% out of tolerance were replaced (there were 10).  I used dogbone type resistors as were used originally.  I picked out NOS and used dogbone resistors from my stock and junk box that had drifted to the correct needed resistance and then repainted them to match the original resistor's color codes.  The replacements may continue to drift, as would most new carbon composition type resistors.  But to me, maintaining the original look is more important than long term reliability of the radio.

Here are some replacement dogbone resistors, ready for installation in the radio.  All have been repainted using hobby paint.   The item at the top is a rebuilt Dublilier Cub capacitor. The procedure for rebuilding these is documented here.

Volume and Tone Control Repairs

The volume and tone controls were of the BradleyStat type, which are difficult to repair or clean.  My process for restoring them is as follows:

• Grind down off the head of the brass rivet on the back that holds the center rear terminal and also the back cover.  Be careful not to damage the terminal, since it must be reinstalled, and take off only the HEAD of the rivet and none of the shaft (just enough to free the terminal lug).
• Remove the center terminal lug and the back cover of the control
• Remove the wiper - it can be pulled from its pivot (careful not to bend it).
• Clean the wiper and resistance element with lacquer thinner on a Q-tip.  Note that the wiper does not directly contact the resistance element, which is wound with circles of wire.  Use a minimum amount of lacquer thinner so as not to damage the resistance element.
• Clean the switch contacts on the volume control (using lacquer thinner on a Q-tip, Caig DeOxit, and finally 600 grit paper when all the above failed to revive the contacts).  Any sanding residue is then cleaned off using lacquer thinner.
• Reinstall the wiper and test the control and power switch for functionality
• Install the back cover
• Replace the center rear terminal lug on the rivet shaft, and then solder the terminal lug to the rivet to hold the back cover and terminal lug in place.

Other Repairs

• New type 59 and 55 tubes were installed
• A type 280 rectifier was installed to replace the 5Z3 (the socket is marked 280 rather than 80)
• About 1' of the line cord was cut off and the plug reinstalled.  The line cord was then safe to use.
• One grid lead was frayed.  It was replaced (in order to do so I had to remove the transformer shield)

Testing

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.  Normal B+ was reached with only 100 volts applied, and the radio worked.  I assume that the high B+ was due to my using a 10mfd input filter capacitor instead of the 8mfd originally used.  Operating the radio on 60Hz power (vs. 25Hz) may have also contributed.  I tried replacing the 10mfd input filter capacitor with a 4mfd unit.  The result was that the B+ was then correct (270 volts) with 110 volts input (rated input AC is 115 volts).  The hum level was slightly higher but not objectionable.  So I will operate the radio through my bucking transformer (set for 110 volts out) any time it is used (which I normally do for all early AC sets).

The radio was then aligned.  It performs very well - it has excellent sensitivity (due to the tuned RF stage) and good tone also.  It performs as good or better than other early 1930's radios (RCA, GE, Philco) - IMHO.

Chassis before restoration	Chassis after restoration (for some reason, the orange paint on the capacitors shows as yellow)

Restored Chassis (the box on top of the power transformer covers a fuse which selects 110 or 220 volt operation)	Cabinet Rear