**this instructable assumes that you have basic electronics knowledge, you can solder, and you have the ability to use basic hand tools.**
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
this radio is housed in a hinged split case. the hinge is at the bottom and the radio splits open right along the center inline with the knobs. it's easy to open so you can replace the batteries. no tools are needed to get inside.
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.