Grundig 2420U questions

[Wildcat]

My buddy's grandmother used to listen to this radio constantly, and it was handed down to me since they are cleaning out his father's house (he passed away a year ago). I immediately recognized the model since my uncle had the same exact radio, which was always in his kitchen while I was young, and ended up at our office in the warehouse being played for nine hours a day, five days per week. This one works fine on both AM and FM--haven't tried SW (shortwave) yet.



All it really needs is some cleaning. The case is unscuffed and unscratched! Even the power cord still looks good (although I may replace it later on for safety reasons). I just had a few general questions before I attacked this thing properly.

1. Any concerns over cleaning the case? I am not going to touch the gold trim on this--you can see the gold lettering for "G R U N D I G" is a little worn off, and past experience tells me I shouldn't touch it much. I have no idea what the enclosure is made of, but I get the impression it may be brittle. As such, I don't even want to unscrew the back cover, although I probably should in case I want to clear away any dust inside. (I would be afraid of mucking up the tuner section though.)

2. Local radio sucks! I just discovered tonight that "PU" on the rear of the cabinet (matching the "PU" knob on the front) is for "pickup," as in a phono pickup (or a tape head, presumably). There is a 5-pin DIN socket on the back of the radio--it appears to be a 180° 5-pin DIN. Idea--I am going to make an adapter cable with a 5-pin DIN plug that leads to either a pair of RCA plugs or a 3.5mm stereo plug, which I can then plug a Chromecast Audio into. Do I have to worry (electrically) about summing the two channels into one? (I don't believe so.) Also, what is the proper pinout for a 5-pin DIN?



I'm guessing that pins 1 and 4 would be the input? I don't know how they are connected inside the radio, but it does say "MONO - PU/TR on the rear. Being that it's low voltage, I can use a signal and poke around on this plug to see which of pins 1 and 4 are live. (I also wonder if the radio has pins 3 and 5 connected, so that the audio could be fed to a tape recorder.)



3. Shortwave. When I played with my uncle's radio, I once pulled in a station out of Romania that sounded like a polka band on speed. I realize there may not be much on shortwave anymore, but is there a type of antenna I could use for that? The radio has an internal FM antenna (which picks up surprisingly well), but has another set of pins for another antenna, presumably for AM and SW bands?



4. Last question--tube life. It's tuning in everything nicely, and the sound is clear. I would guess the tubes are OK? I am tempted to peek and see what tubes are in the radio. Any clue as to what the original tube brand(s) might have been in a Grundig?

Neat thing I found on the rear--a now-rare 2-pin DIN plug for an external speaker.

 

[Tom Bavis]

Tubes are probably Valvo/Philips (Telefunken was a competitor). If the green tuning eye is still bright, the tubes don't have a lot of hours (or it's been replaced!) You can download the schematic from Radiomuseum.org: https://www.radiomuseum.org/r/grundig_2420u2420.html

 

[Wildcat]

If the green tuning eye is still bright, the tubes don't have a lot of hours (or it's been replaced!)

It's visible but not overly bright. I noticed there is a set of tubes on the Bay for this radio, from Bulgaria, claiming to be NOS. But if I need only the Magic Eye, I may just keep watching for one and pick it up later this year.

I plugged it in--there is a constant rustling from the speaker regardless of the volume setting, even when selecting PU. I am thinking I may need to open it up and reseat the tubes, or go a little further and clean all the contacts. Beyond the noise it sounded better than I remember it! Tuning isn't the greatest--we have a lot more FM stations crammed into the dial now than we used to, and that internal antenna isn't doing it many favors either.

I don't think I even want to get into recapping this thing.

 

[Patrice B]

Rustling? Could be a tube or bad caps in the power supply. Ideally, you should recap at least the power supply and the caps in the audio section (don't touch caps in the radio section!). These German radios are a pain to work on, believe me (crammed space under and the piano keys mechanism)!

 

[Wildcat]

I don't think I'd have patience for a recap on this radio (20 years ago, maybe ), but if I could at least get to the power supply section, yes, I would probably do that first. Did they even use electrolytics in these radios back then? Or are these other types of caps that deteriorate? I won't touch the radio section at all.

 

[Patrice B]

Electrolytics and probably a Selenium bridge...

 

[Wildcat]

Well, this saves me some work! Found this on Amazon, and others report using it to feed an MP3 player to a 1960s European radio.



$3.20, shipped!

 

[gadget73]

I aways just used glass cleaner on the plastic and furniture polish on the wood for my Euro radios. The gold plating will wear off if you do much beyond wipe it with a damp cloth though. Glass cleaner is fine, do not polish it.

A long wire for shortwave is fine. If you're just casual listening, honestly the length is not important. Run a wire out to a nearby tree or whatever and it will pull in AM and SW pretty well. The longer the wire the better usually. Mine is probably 75 feet, run from the upstairs window to the shed out back.