**this instructable takes into account that you're familiar with basic electronics, soldering, and basic hand tools.**
this instructable is written around the sylvania 4P19W transistor radio. this size radio is what was called a coat pocket radio. this radio is unique in that it only uses 4 transistors. the fact that it only uses 4 transistors gives it a slightly longer battery life than the more common 6 and 7 transistor AM radios of the time. the tradeoff is in it's performance. this radio is fine for listening to local AM stations but don't expect it to pull in signals from far away. the reflex circuit allowed a transistor to be used for two things at once, in this case it handled RF as well as audio at the same time.
this model of radio is common on ebay for $10 or less. they use older styled oval metal cased transistors so they are of interest to the vintage tech geek. the reason i have heard for these being common is they were given away as a promo when you bought a new sylvania TV set.
Step 1: Let's Dig In!
to get inside you need to remove the back cover of the radio. this is also how you'd open it up to replace the battery. many old transistor radios are setup like this were you pry open a lid to get inside. once inside you will find the circuit board (chassis) and the schematic.
note the battery holder. is it corroded from an old battery left in it? if it is, replacements can be found online. radio shack used to carry 9v clip on terminals but i'm not sure if they still do.
the circuit board is held in the plastic housing by 1/4" hex head bolts. note the two i'm pointing at in pic 4. you will be removing those two and the two on the right edge near the battery connector. no need to remove the remaining two as all they do is hold the tuning capacitor in place.
once the screws are out, you can carefully lift the board out. be careful with the speaker leads.