Grundig Hit Boy++


Recently I bought a old, broken portable radio ("Kofferradio" in german) on a flea market in western rural germany. Although the seller promised it to be working, I was rather sure that it would be broken. Which I hoped for, knowing that I never would be able to rip a working one apart. Luckily, it really was broken. Perfect, lets go on!

Grundig Hit-Boy N210a


This $file one. A typical 70ths portable radio. Fully transistorized, Super-Heterodyne, three bands, mono. A total of 7 discrete transistors. One single 9cm permanent magnet speaker with hard paper suspension. Ah, those where the days!
Might also be the older version (without the "a"), i don't know. I really like the very classic look of it.



Amp


I used a single TDA2030, mostly because I had 5 apiece. One spare. They sound really nice. A bit overboard for a thing like this, but eh. Who cares. I used the reference design from the data sheet (just a few caps and resistors). It sounds very nice with the original speaker, not tinny like more modern portable radios, but bit hollow. A very distinct sound I closely connect to (better) radios from this era. The really bad, tinny sound came later, with the ultra-cheaps of the 80s and 90s.
Somehow these devices are never very good with music like metal, they resonate much to easily. But with Pop from the 50s, 60s, 70s and 80s and most wavey stuff I really like the sound.

The TDA needs around 7V ot 8V to operate nicely. Supply is either USB or a single LiIon cell and a cheap Boost converter. Sure, those tend to produce noise, but meh, its not Hifi anyway. Actually, cant make out the difference between the boost converter and a linear PSU. Not with this overall construction.

Power


A single 18650 cell, charger and holder. Very simple and fits neatly, half the original battery compartment actually becomes cable compartment.

Sources and Input


I put a two-way 6-positions rotary switch in the place of the tuning wheel (using the original cap). It selects the input source on the first way, the second way gives power to the device on that source. Kinda fitting, eh?
Currently the only sources are line in and the internal MP3 player. But I plan to add Bluetooth and maybe radio. Possibly even a raspberry pi zero w.

The line input uses the original 3.5mm headphone output jack. The original mains port houses a USB A connector for the MP3 Player.

MP3 Player


I had a simple MP3 Player with RF-transceiver and cigarette lighter plug for use in cars. I have no car. Good, since the player has a nice feature: it starts playing as soon as it hast power. So it will start playing as soon has I "tune" to "Station" 2 ;)
Second awesome Feature: it has a wee tiny Display. I glued it behind the hole left by the former band selector switch on the Backside. About a third is hidden this way, but enough is visible to read the (scrolling) track name. Looks awesome.
The Player provides an SD card slot and an USB Port, the latter is glued into the hole left by the mains connector.
Since its glued to inner backside of the case, the controls are not accessible any more. Which is ok, because the player start playing as soon as it gets power and remembers its settings (random mode).
The Radio had a third control, named "KW Lupe", I guess some fine tuning thing for short wave (it was a adjustable capacitor). It was brittle and broke apart as soon as I touched it, but the Metal parts of it actually act as plunger now. For a little tactile switch which I connected to the player "next" button.

A second, smaller Boost converter is needed to provide 5V from the LiIon Cell.
There was a switch for AM/FM selection on the radio's backside. It miraculously fitted the tiny display from the mp3 player quite well.

Bluetooth receiver


A project for days to come!

Radio receiver


Maybe? I dont know. Radio does not play much Music i like nowadays.

Result


I really like the look. The hole where once the antenna is clearly a flaw, but its just there because i have not yet decided what to do about it. Could become a charging port, or i might put back the original 9now pointless) antenna.

Glor glory hot glue!

total: 125.78ms (include: 2.4, request: 0.93, trace: 0.42, init: 3.39, load: 0.01, parse: 114.97, menu: 0.99, template: 2.59, minify: 0.09)