I acquired this 1955 Zenith Royal transistor radio recently and when I inspected the outside, it was in very good condition, considering it's 63 years old. Everything was there, including the original sticker on the back of the radio. I did some research on this particular radio and apparently this was the first transistor radio that Zenith made. It wasn't the first transistor radio made, that credit goes to Regency that came out with the TR-1 in 1954. My radio was made using point-to-point wiring, just like in the old tube radios. Printed circuit boards would come later. Interestingly, this radio was made with a Nylon cabinet. When it was marketed, it sold for $75.00, a princely sum in 1955, equal to around $700.00 today! The transistor radio was not yet something that was bought for the typical teenager to take to school. That would come when the Japanese got into the market and started to make them much cheaper.
Step 1: Tools and Parts Needed to Work on This Radio.
1) Soldering Iron
2) Radio Solder
3) Assorted screwdrivers, Slot and Phillips of different sizes.
4) Long-nosed pliers, small locking forceps and/or tweezers.
6) Signal Generator (Only if signal tracing or alignment is required)
7) Oscilloscope (Only if signal tracing or alignment is required)
8) Low voltage power supply
9) A small of piece of sheet steel (1 mm thickness approximately) Could be obtained from an old can or tin.
10) Methyl Hydrate
11) Plastic basin
12) Medium sized artist's paintbrush
13) Fine steel wool, emery cloth or small fine wire brush.
14) Electrolytic Capacitors, 50, 40, 3 and 16 Microfarads rated at least 6 volts. Pick the closest values you can obtain.
15) Hot melt gun and glue.
16) Household ammonia
17) 4 Penlight batteries also known as AA size
Most of these items can be obtained at either an electronics, hardware or home improvement store.
Step 2: Evaluating the Condition of the Inside of Radio and Taking the Speaker Out.
The radio comes apart with 2 screws which when removed allows the back and front pieces to come apart. The chassis with the components and wiring comes out of the front piece of the radio by removing 1 screw and one metal standoff. The two dials in the front of the radio can be easily removed with a little force from a flat blade screwdriver prying them up.The speaker is attached by two metal screws to the back of the battery compartment. The battery compartment has room for four "penlight" (AA) batteries providing six volts to the radio. The battery compartment showed a fair amount of corrosion from battery leakage over the previous 63 years which had gone underneath the battery compartment and eaten through a couple of wires. One of the metal "fingers" which make contact with the battery terminals was broken off. I would need to make a new one out of sheet metal. Overall, the radio looked in fairly good condition inside with nothing that would keep it from being repairable. All the components were there and the wiring was mostly still intact. Once I removed the chassis, I took the two screws in the battery compartment out and the speaker came free. Underneath, I could see a couple of wires that had been eaten through with corrosive battery liquid. I hooked up a power supply to the radio and set the power supply to six volts. I heard a slight rushing sound coming out of the speaker. I figured that there was probably not much wrong with it. There were a number of electrolytic capacitors that needed to be replaced after I washed the chassis with methyl hydrate. The speaker would need to be removed as it could be damaged by the methyl hydrate.
Step 3: Rinse Chassis in Methyl Hydrate.
I rinsed the whole radio chassis in methyl hydrate because I have found this substance very easy to work with and does a good job of cleaning off debris and battery acid. Using the artist's brush I gently cleaned off some of the rust and oxidation found on the chassis and battery compartments. The methyl hydrate didn't seem to be too hard on the wax that holds the ferrite rod coils in place, but I used the methyl very sparingly around the ferrite rod anyway. I was mostly concerned with cleaning out the battery compartment and the surface and underside of the metal chassis. I allowed everything to air dry in the sun. Once dried, I took the transistors out of their sockets and cleaned the leads with a fine wire brush. I reinserted them in the sockets a few times to make a better connection.
Step 4: Replace the Old Electrolytic Capacitors With Modern Ones.
In the picture of the lower side of the chassis, four white electrolytic capacitors can be seen. These need to be replaced with modern ones. When replacing with modern ones, note that if the positive side isn't marked with a + sign, it will be marked red on the old capacitor. The modern ones should be clearly marked. It might be hard to find capacitors with exactly the same values, but just try to get them as close as possible. None of the values are super-critical.
Step 5: Make a New Metal Battery Finger and Attach.
I cut and bent a battery "finger" out of thin sheet metal to approximately the same size and shape of the original. I soldered a small copper wire to it and drilled a small hole approximately 1/16 of an inch right next to it so the wire could be attached to the place where it originally connected to. The new "finger" was then glued into the place where the old finger was located with hot melt glue. I also put some hot melt glue on top of it allowing for the top to bend as it comes into contact with the battery.
Step 6: Repair the Ground Connections
I repaired the ground connections and reconnected the speaker. I took some steel wool and made a final cleaning of the fingers that make connections to the batteries. The radio worked the first time which is surprising, considering its age.
Step 7: Final Cleaning and Assembly
I Cleaned the outside case with a cloth or paper towel using household ammonia and water. The years of dirt came off easily. When I was satisfied with the appearance, I put it all together. Since this radio is mainly for display purposes, I will take the batteries out when I am finished.