How to Repair and Revive an American Made Zenith Transistor Radio.




Introduction: How to Repair and Revive an American Made Zenith Transistor Radio.

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this instructable takes for granted that you can solder, work with small parts, read values on capacitors, and have a basic understanding of electricity.

transistor radios have been in production for over 50 years now. even early ones are common finds at yard sales and fleamarkets. they were the ipod of the 60's and 70's and many have become sought after collectibles.

in the mid 50's an american company named regency produced the world's first commercially made transistor radio. right on their heels where several other american companies and so the battle for the transistor radio market began.

transistor radio manufacturers came and went. by the late 50's, the japanese began to produce transistor radios at prices that american industry couldn't compete with. some american companies quickly moved production to japan, others just had their radios made for them. one company stuck it out till the bitter end, it's name was zenith.

zenith radios were generally better built than any of the competitors and priced accordingly. some models like the transoceanics cost as much new as a decent used car would have cost at the time. because of their quality, many still survive. this instructable will deal only with large zenith metal chassis transistor radios. much of the info provided though does carry over to other brands of metal chassis transistor radios.

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Step 1: Getting Inside Your Radio

a great many of the large lunchbox sized radios came in a leather or pleather case. the leather ones were sometimes all leather with a metal face that the radio bolted into or a metal case with the leather glued on. the pleather (fake leather) radios were also made this way but it was more common to find them as a fiberboard box that was wrapped in a leather looking plastic material.

most of these covered radios used a snap clasp to keep the back of the radio shut. to change batteries you unsnapped the clasps and flipped the door up. its not uncommon to find these clasps broken off or frozen shut. if the clasps are broken off, you'll have to conjure up some way to keep that door shut while moving the radio around.

if the clasps are frozen you may be able to save them. take a can of wd40 and put the straw on it. give the clasp a shot right were both halves meet. let it sit a minute then take a pocket knife and work the blade into it trying to split both halves. if you're careful you'll pry them apart without breaking anything. the wd40 may stain a leather cased radio so keep that in mind.

on the zenith royal 1000, 2000, 3000, and 7000 series radios there is a mechanical fastener to access the battery area. these radios are much more complicated internally and beyond the scope of this instructable though some of the info presented here applies to those sets.

Step 2: Woohoo! We're Inside!

bask in the luxury of a metal chassis, hand wired radio. while other manufacturers quickly moved to PC boards, zenith continued to make it's better radios on a hand wired steel chassis.

inside the radio you should find the chassis, a battery holder, and if you're lucky, a transistor placement diagram. that diagram is your friend if further repairs need to be made or if some curious person plucked out some of the transistors.

plucked transistors?
yes! on many zenith metal chassis radios, the transistors are in sockets for easy replacement.  from here we'll address the battery compartment and transistors.

Step 3: Removing the Chassis

the chassis will be bolted in. chances are the face of the radio will serve as a mounting place for the chassis. this is common on zenith metal chassis radios.

first pull off the knobs. the chassis wont come out if the knobs are still on the radio. this may get frustrating. try as best you can with your hands. pull the knobs straight out. don't wiggle. wiggling could lead to breaking things IN the radio. on zenith transoceanics, the band select knob has a set screw. you cannot remove the knob until you loosen the set screw. always check for set screws when you come across a stubborn knob that cant be removed easily. if pulling them by hand seems impossible, you need to come to grips with two possible scenarios..
1) the knobs may break on removal
2) the radio may be damaged while trying to remove the knobs

accepted these terms yet? if not, come back when you're ok with these terms.

stuck knobs.. what to do?
one option is take a screwdriver or two and use them to pry the knobs straight out from the radio. use a piece of cardboard or heavy fabric to protect the face of the radio as you pry. the second option is to make a sling. i have never tried the sling method and you will have to research that on your own.

peek around and look for bolts that attach the chassis to the face. remove those and keep track of where you pulled them from. a simple hand drawn diagram works wonders for this if you have a poor memory.

before lifting the chassis check for an earphone or external power jack. that jack will be hardwired to the chassis usually by an absurdly short bit of cable. those jacks need to be removed. if not, you cant lift the chassis out. some use a conventional nut, some use what looks like a washer with two notches. the washer with two notches can be the most frustrating fastener you have ever dealt with. there is a proper tool for those but most folks lack it. a pair of snap ring pliers with thin tips *might* be your best recourse.

also while lifting the chassis, keep an eye on the speaker. on some radios the speaker is attached to the face, on others it's attached to the chassis. if yours is bolted to the face, you may have to unplug or desolder the speaker wires to liberate the chassis.

Step 4: Batteries and Neglect, a Transistor Radio's Biggest Enemy

basic AM transistor radios tended to have a very long battery life. lunchbox sized radios with their larger batteries would have a battery life measured in a year or two depending on use. i currently have one zenith that's going on three years on the same set of batteries and i use it nightly with a earphone.

because of this very long battery life, owners tended to forget how long ago they had installed the batteries in their radios. modern batteries like duracell or energizer have much better seals than old batteries did. old batteries would leak with age and ruin radios.

battery acid damage can be seen in the pics. the acid corrodes anything metal it comes in contact with. on fiberboard cased radios it can ruin the casing. on the pic of the back door of the radio there's a big "pimple" towards the top of the radio. that's were the fiberboard absorbed battery acid. all that can be done is clean it off as best you can.

fortunately zenith anticipated such neglect and every lunchbox portable i have seen they made has the batteries at the bottom of the case and in a plastic sleeve of some kind. this sleeve does come apart for cleaning. new wires can be soldered in if need be. the ends of the sleeve are keyed and only go back on the tube in one direction.

if your battery sleeve is damaged beyond repair or flat out missing, you have some options. you can find an original or repro holder on ebay or the antique radio forums or replace the original with a different style pack.

my favorite solution is to get an AA battery holder with the same number of cells as the original had. you can find 3000mA AA rechargeables easily on ebay. on these radios, modern AA batteries will last a very long time, they are cheap, easy to find, and weigh far less than the original C or D batteries the radio originally used.

despite the years, the acid is still corrosive. do not rub your face or eyes if you have been cleaning off old battery acid damage. wash hands as soon as you are done doing this cleanup.

Step 5: Cleaning Up Battery Corrosion

once again..

despite the years, the acid is still corrosive. do not rub your face or eyes if you have been cleaning off old battery acid damage. wash hands as soon as you are done doing this cleanup.

battery acid can be neutralized with a solution of baking powder and water. coke also works but then you have stickiness to contend with and must wash everything out with plain water. corrosion on the battery terminals can sometimes be chipped off with an awl or screwdriver facilitating cleanup. a small wire brush comes in handy as well.

pics are of the battery compartment after cleanup.

Step 6: Chassis Is Out, Capacitor Check Time

if you've ever worked on ANY old audio gear, you have surely replaced caps. capacitors go bad with age. there's no way around it. a radio from 1970 is now over 40 years old. the electrolytics were not designed to live that long. they must be replaced.

signs of bad electrolytic caps..
radio has weak or tinny audio on known strong stations or obvious leakage around the capacitor.

the first picture is of the type commonly found in very old transistor radios. its basically a little black tube with a dab of some red epoxy on the end. if you see these, replace them. its rare to find this style cap that has not failed. sometimes they are in a different color but still have the characteristic dab of epoxy on the end to seal them. they always have the value written on the side so you'll know you're looking at a capacitor.

the second pic is of a more modern capacitor. on this particular radio, it looks like somebody may have replaced some caps already. since the radio was playing ok, i'm leaving those alone.

replacing old caps.. two schools of thought.
1) keep it original. if you have a valuable radio, gutting the old capacitors and restuffing them with physically smaller modern equivalents is an option. this gets the radio working again and keeps it looking original.
2) just use modern parts. this is what i do. i use my radios and most of them are not in collectors condition anyways.

when replacing old caps, be sure to install your replacement in the same exact position as the old one. this is important. being careless in how you stuff them back into the chassis can actually knock the radio out of alignment and then you have a poor performing radio.

be sure to observe polarity. most electrolytics have a + and  - terminal. your replacements need to be wired the same way if not you can damage your radio when you power it up.

while you are in there. its a good time to spray the volume control, tone control if it has one, and band select control if it has one, with contact cleaner. spray the switches and potentiometers and then work the control a few times. this will get rid of any annoying crackling. i have used wd40 for this but the proper product is electronic contact cleaner spray. it can be purchased at radio shack or online.

Step 7: Transistorized for Your Instant Entertainment

zenith used socketed transistors for many years after the rest of the industry went to circuit boards with soldered in transistors. this is a more expensive way to do things but also makes troubleshooting a breeze. if your radio is missing any transistors, refer to the diagram usually found on the battery door for transistor part numbers.

zenith like many other "want to be special" manufacturers used their own numbers on transistors. this was a greedy way of getting people to buy parts from them. some searching online will yield a zenith transistor cross reference chart. this chart will decode zenith part numbers to the industry standard numbers which will allow you to find replacement parts at any electronics parts vendor.

zenith transistors come in two flavors, 3 and 4 legged. the 3 and 4 legged ones can be replaced by common part numbers. once again refer to a cross reference chart. on the 4 legged transistors, one lead is just tied directly to the metal case of the transistor.

so you couldn't resist. you popped one out and cant figure out how it goes back in huh?
the 4 legged ones can only go back in one way without bending the legs up. the 3 legged ones can be easily put in the wrong way. if you look closely at the socket you may see a little dimple on the side of it. that dimple is meant to line up with the color dot on the transistor. this trick only works if you have an original transistor in that socket.

since you have the chassis out. this is a good time to make sure the correct transistors are in the correct socket. using the chart on the battery door and noting the orientation of the chassis. this should only take a few minutes and save you lots of future frustration. sometimes a substitute part number was used in a repair and it may not match the chart. note which part number doesnt seem right and put everything back as you found it. the radio may be ok and you just have a sub part number in there.

transistors can go bad but that is beyond the scope of this instructable.

Step 8: Reassembly and Case Cleaning

your radio is ready to be reassembled. might as well clean the case up while things are apart.

on plastic, metal, or plastic covered radios you can have amazing results with a very unlikely product, gojo hand cleaner. yes, the same gojo used by mechanics. get the gojo creme, NOT gojo with grit or pumice. wipe it on, work it in with your fingers. let it sit for 5 minutes or so, and wipe it off with a clean terry cloth towel. the results are pretty amazing. even nicotine tinge comes off without too much work.

leather covered radios can be cleaned with leather cleaning products available at auto care stores. if you're radio has no collector value. you can use gojo but it will darken the leather.

its best to not touch the dial face as the numbers my wipe off. blow out the dust and let things be.

once done cleaning, put your radio back together and load it with batteries. on my particular set, one knob was cracked so i had to find a somewhat suitable substitute. in this case, a knob from an old record player worked out.

Step 9: Put It All Back Together and Enjoy!

these old zenith radios are great for late night listening. put them on AM, and slowly tune around. you'll be amazed at the far off stations you may pick up. best results are attained just by sitting outside in the evening. when night falls, AM signals start to skip across the atmosphere and land in places they normally don't cover.

enjoy your classic piece of american craftsmanship.

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    9 Discussions

    Freshy Smooth

    how many cells does the 820 have? Mine didn't come with a battery pack.


    Reply 3 months ago

    Thank you,
    I had a 6 cell battery pack aa batteries. I filled it up and connected it to the connector in the radio. It works fine. Is this 9 volt battery pack oky?


    Reply 7 months ago

    4 I believe. (edited)


    Question 3 months ago

    HI ,
    Nice article. I purchased the zenith royal 820on eBay.
    It came with a small 9 volt battery adapter which someone
    Change to from the original battery holder. It works, but I am wondering
    If it is oky, and how long that battery will last. Also it has the 9 volt jack to
    Attach a power supply that plugs into std 110 volt outlet. What size adapter should
    I use as far as milli amps is concerned.
    Thanks Mike


    Answer 3 months ago

    The radio was intended to run on 4 C batteries I believe which is 6v. Its not uncommon for people to run them off 9v but due to the small capacity of the square 9v batteries, it wont run too long. Best bet is get a 4 cell AA battery holder off ebay and wire that in. Modern AA batts will last longer than the old C batteries did back when the radio was made. Be careful with polarity when you swap out the battery holder. some old transistor radios used chassis positive as ground. just follow the way it was wired.


    7 months ago

    Just acquired a Zenith Royal 1000-D, but it had no battery pack. What should I build or find to replace it?


    Reply 7 months ago

    While you can find the original pack, Ive been keen on replacing all of mine with AA cell holders. Modern AA alkalines pack as much punch as D batteries did when these were made.


    7 years ago on Step 8

    This is fantastic. I actually used to own an old Zenith and Transoceanic radio that I found at a farmers market. The transoceanic actually still worked after all those years, I would listen to AM radio stations late at night on its and some of the stations would come in faded and create this fantastic illusion of going back in time. Absolutely phenomenal radio.