in this instructable we'll be covering the basic rebuild of an early portable transistor radio. these big transistor radios where called "lunchbox radios" and were how folks took their entertainment outdoors 50+ years ago. some folks called them camp radios.
portable radios were not a new idea but transistor technology meant your batteries could now last a year or so instead of a few hours like they did with tube portables. eventually the big lunchbox sized AM only radios fell out of favor and were replaced by shirt pocket AM radios that weren't much bigger than our current cellphones.
when it comes to first generation transistor radios, the olympic 447 is in a league all it's own. let's say your a radio manufacturer in the 1950's but not one of the big boys. you're anxious to get on the transistor radio bandwagon but don't have the R&D budget that the big boys have. what to do?
you take one of your current vacuum tube radios, have your engineers redesign the circuit, and shove the transistor leads right down the same sockets the tubes used to plug into! that's what the 1956 olympic 447 is all about.
using only 4 transistors in a circuit that used to be setup for 4 tubes, this early transistor radio performs quite well despite it's low transistor count. the big ferrite antenna helps it pull in stations much better than the 4 transistor sylvania reflex radio i have in a different instructable. power was furnished by (2) 9V brick style batteries. in a radio like this, batteries of that size would easily last over a year with daily use.
ok, enough history, let's see whats inside.
Step 1: Let's Peek Inside and Do Some Basic Tests
pic 2 is of the radio opened up. the radio runs off 9vdc. it has two battery connectors but both are wired in parallel. now is a good time to see if your radio works at all. do not exceed 9v input to the radio. you risk damaging some VERY hard to find transistors. this radio will power up with 6v-9v. you can use a regulated power supply or a 9v battery and alligator clips.
look at the old battery connectors coming out of the radio. on the connector at the end of the cable, the terminal at the very end (not where the wires come in to the connector) is the positive terminal. apply power, turn the radio on at full volume, and tune around. get anything? any sign of life is good. it's possible your radio may play loud, in that case back down on the volume control.
your radio should have a pictorial diagram inside like the one in pic 3. it may be of help here. on a humorous note, the pictorial diagram shows the transistors in transistor sockets. the actual production model just re-used the tube sockets.
are you getting lots of hash and noise but nothing intelligible? is the radio right next to a computer or lithium battery charger? those two things can generate plenty of RF noise on an AM radio. relocate the radio and try again or shut off the possible noise sources. try again.
get anything now? if your radio picks up anything, that's a good sign. tinny, weak, or distorted audio we can fix. if your radio is totally dead you may need to do some simple checks.
take a multimeter and check for continuity from the positive battery terminal to the metal radio chassis. the radio should be switched on for this test. like many early transistor radios, this one uses positive ground. you should have continuity. if you don't, you need to find out why.
look at the volume control. the power switch is built in. it's got two terminals grouped together. those are the power switch terminals. check for continuity here. you should have continuity when the radio is switched on. if you don't, your power switch is bad and that would cause a dead radio.
if you have a totally dead radio, there is still hope but you may want to consider the fact that your radio may have issues beyond the scope of this instructable.
next up, we get inside.
Step 2: Let's Dig In!
in my radio there was a blue wire that didn't belong. it was attached to the antenna. it's seen in pic 1. somebody added it so they could improve AM reception. being in a major city, this wire was an unnecessary mod.
once you have the two mounting screws out, the radio chassis will just lift out with knobs and all. pic 3 shows the front of the chassis, pic 4 shows the back of the chassis. extra care must be exercised at this point. the speaker is easily damaged as it is old and brittle. the leads on the transistors are easy to bend and short out.
the handle comes off easily and should be removed while you are working on the radio. don't trust the handle to hold the weight of the radio when it's not in it's cabinet. the cabinet keeps the handle from popping off.
on the bottom you will see a removable metal cover. this cover is held in place by two bent metal tabs. bend one enough to wiggle the cover off and it will tilt out of the way and come off. no need to bend both tabs nor bend one fully straight. fully straightening these tabs can cause them to break off.
Step 3: What Are You Looking At?
looking at pic 1 you see the antenna (long black rod with wire wrapped on it), the tuning capacitor on the left with the knob on it, the volume control and power switch on the right with the knob on it, and two transformers bolted to the chassis near the volume control.
in pics 2 and 3 you see some close-ups of the blue raytheon transistors used in this radio. my radio had 1956 date codes on the parts. keep in mind the worlds first transistor radio was sold in 1954. technology didn't advance as fast is it currently does so this radio was still somewhat of a novelty in 1956.
resist the urge to touch the transistors. the leads on them are delicate. do not "straighten them out". if there's a risk of two leads touching, move them enough to prevent a short and that's all.
Step 4: Re-cap Time
you can repair or restore at this point.
repair means making it work again with no regard for keeping it looking era correct. this means replacing old parts with new parts.
restore means making it work again while keeping it looking era correct. this means you will be using new parts where required but may go to extremes like hollowing out old capacitors and stuffing the modern part inside to keep the radio looking original.
i use all my radios and most are in less than collector quality so i opted to repair with modern parts. when replacing old caps, replace one at a time, always observe proper polarity, and try to use the same or a slightly higher value. never use a lower value.
in pic 3 you see my radio after capacitor replacement was completed. modern parts are substantially smaller than their vintage counterparts. it's extremely important that you try to install the new caps in the same place as the old caps. this will help keep your radio aligned. when the RF alignment was performed, the position of the parts comes into play. the less you disturb things, the more likely your radio will work right from the start.
* a note about polarity *
this radio, like many early transistor radios, uses positive ground. that big clump of capacitors with all their + sides wired to ground is intentional.
Step 5: Clean and Lube
in pic 2 you see the bearings on the tuning capacitor. the grease on these hardens over time making the control hard to turn. a drop of oil on both the front bearing and that back bearing is all that's needed. once you got the drops of oil on there work the control back and forth and you may notice it free up a bit.
since this radio chassis comes completely out of its plastic enclosure, you are free to wash the cabinet in the sink with dish soap, a soft brush, and warm water. that should get it cleaned up nice. if you remove the knobs, they can also be cleaned with a brush, soap, and water.
Step 6: What About the Weird Battery?
go ahead and load up the holder with batteries and power the radio up. if all went well, it should be working with good strong audio. if you're radio was dead on the previous test at the start of this instructable and it's still dead, you have other issues to contend with, some being beyond the scope of this instructable.
possible issues causing a dead radio..
1) cracked circuit board or cold solder joint - examine the circuit board with a magnifying lens and re-solder or repair any cracked traces or cold solder joints.
2) broken antenna leads - there are several very thin wires that go to the antenna. they should all be connected somewhere. none should be lose. look the antenna over closely. sometimes the break can be found and re-soldered.
3) power issue - with the radio switched on, you should see battery voltage when you put your positive meter lead on the chassis and the negative on either of the two switch terminals. if you see a negative voltage when you put your meter's positive lead on the chassis, your battery pack is wired backwards. that will cause the radio not to work.
4) you have a dead transistor or RF transformer - this is beyond the scope of this instructable.
Step 7: All Is Well? Enjoy Your Radio!
what to listen to on AM?
most major cities have sports and news talk stations. if you're not into that and you think you might get into collecting old radios, look into purchasing an AM "talking house" transmitter from ebay. these are low powered AM transmitters that can be fed with a computer or MP3 player and will easily cover the average house and yard.
expect battery life to be over a year or so on these radios. don't forget to remove the batteries if you wont be using it for a long time. alkaline batteries can leak over time.