Excellent restoration, I used them in my work on old telephone equipment in the 80s, the metal band on the head had a leather cover. Best regards from Argentina.
Nice, thanks for the info! I was wondering if there was some sort of cover on them, but couldn't find reliable info. I might stitch something together! Greetings back from Austria!
The results are beautiful. I was afraid they would lose their original character, but you kept it intact and enhanced it greatly. You can use headphones like that as a detector for a capacitance or induction bridge. That’s what I have for my General Radio 650. Its signal source is a fork-tuned “hummer.” It’s appropriate to wear a jacket and tie when using this equipment.
Thanks! While I don't do "museum style" restorations and sometimes have to rework some details, I do my best to keep the original look and feel to all of the devices I take care of. After all, I want to use them occasionally, even if it's just for the nostalgia of it :)
This headphone model first appeared on the market in 1925 in Germany under the name ‘EH333’ and was produced until 1945. It was produced by Telefunken for crystal radio receivers - relatively cheap to manufacture and allowing the air gap between the diaphragm and magnetic poles to be trimmed to maximise sensitivity. Interestingly, they were also widely used in the army!
Oh! Thanks for the info! I don't think they were "early ones", so more likely around the 1945 range. Maybe even surplus military? Who knows. The auction was from an estate sale, so the original owner sadly passed away some time ago.
Guessing at 2m of wire, 2mm outer diameter, that will give you ~50pF to free space. 1kHz will give you 0.3uA/V, or the equivalent of 3Mohm between the unconnected side and generator ground. Yes, that should be audible. The transmission-line- contribution is less than that. Silly note: The English alphabet used to have the letter þ (thorn), 'th', which in some scripts looked somewhat like y.
I also have a pair of headphones in this style but in 2500ohms each cup, I can also hear audio in them when only one wire is connected, as per why there is actually a bit of black magic and science behind it, But in short when you connect power on to an open circuit the electrons don´t really know the other end is open until they gotten exited to the other end, plus some stray capacitance and magnetic response in the drivers you get enough signal to get some audio out of them. electricity is a weird thing sometimes lol
The most interesting thing was the phones working with just one wire, off course this happens because of the high impedance of the phones but the process puzzles me, yes the signal may be irradiating like an antenna by the other wire even being a low frequency so the current flows anyway...this deserves a little more study. Are the connection wires twisted? If they are this theory breaks apart. I will try with my high impedance phones.
A very fine brush and white paint... It is slightly easier, when you can be sure that the black base color is solid enough for a bit of scraping, but I was not in this case. Very carefully painting it in and quickly brushing away anything that "leaked" out. Since I had to work close up with my magnification goggles, I could also not film it. I tried, but either me or the camera couldn't see anyhting 😊
I think the fact that you can hear the tone even with an open circuit has to do with the high voltage driving the headphones being able to actually put a certain amount of static charge into the coils.
Interesting idea; though I haven't tried it with high voltage just yet. Just the 10-15V that my generator gives out are enough to faintly hear the signal.
Excellent restoration, I used them in my work on old telephone equipment in the 80s, the metal band on the head had a leather cover. Best regards from Argentina.
Nice, thanks for the info! I was wondering if there was some sort of cover on them, but couldn't find reliable info. I might stitch something together! Greetings back from Austria!
En los 80s los seguiamos usando? Saludos tambien desde Argentina
Nice restoration! As for the signal coming through, I'd rather say it's capacitive coupling to grounded parts including you.
The results are beautiful. I was afraid they would lose their original character, but you kept it intact and enhanced it greatly. You can use headphones like that as a detector for a capacitance or induction bridge. That’s what I have for my General Radio 650. Its signal source is a fork-tuned “hummer.” It’s appropriate to wear a jacket and tie when using this equipment.
Thanks! While I don't do "museum style" restorations and sometimes have to rework some details, I do my best to keep the original look and feel to all of the devices I take care of. After all, I want to use them occasionally, even if it's just for the nostalgia of it :)
This headphone model first appeared on the market in 1925 in Germany under the name ‘EH333’ and was produced until 1945. It was produced by Telefunken for crystal radio receivers - relatively cheap to manufacture and allowing the air gap between the diaphragm and magnetic poles to be trimmed to maximise sensitivity. Interestingly, they were also widely used in the army!
Oh! Thanks for the info! I don't think they were "early ones", so more likely around the 1945 range. Maybe even surplus military? Who knows. The auction was from an estate sale, so the original owner sadly passed away some time ago.
Guessing at 2m of wire, 2mm outer diameter, that will give you ~50pF to free space. 1kHz will give you 0.3uA/V, or the equivalent of 3Mohm between the unconnected side and generator ground. Yes, that should be audible. The transmission-line- contribution is less than that.
Silly note: The English alphabet used to have the letter þ (thorn), 'th', which in some scripts looked somewhat like y.
I also have a pair of headphones in this style but in 2500ohms each cup, I can also hear audio in them when only one wire is connected, as per why there is actually a bit of black magic and science behind it, But in short when you connect power on to an open circuit the electrons don´t really know the other end is open until they gotten exited to the other end, plus some stray capacitance and magnetic response in the drivers you get enough signal to get some audio out of them. electricity is a weird thing sometimes lol
The most interesting thing was the phones working with just one wire, off course this happens because of the high impedance of the phones but the process puzzles me, yes the signal may be irradiating like an antenna by the other wire even being a low frequency so the current flows anyway...this deserves a little more study. Are the connection wires twisted? If they are this theory breaks apart. I will try with my high impedance phones.
It is of course nowhere near full volume, but it is there. I don't think the lines are twisted, but it's hard to tell under the outer sleeve.
How did you redo the white lettering? It came out very nice.
A very fine brush and white paint... It is slightly easier, when you can be sure that the black base color is solid enough for a bit of scraping, but I was not in this case. Very carefully painting it in and quickly brushing away anything that "leaked" out. Since I had to work close up with my magnification goggles, I could also not film it. I tried, but either me or the camera couldn't see anyhting 😊
I think the fact that you can hear the tone even with an open circuit has to do with the high voltage driving the headphones being able to actually put a certain amount of static charge into the coils.
Interesting idea; though I haven't tried it with high voltage just yet. Just the 10-15V that my generator gives out are enough to faintly hear the signal.
In this video, somebody from Switzerland has done a restoration on a a similar headphones:
ua-cam.com/video/98pUBuTar_s/v-deo.html
Indeed very similar; I think I got lucky in so far as mine only had cosmetic damage. Nothing was bent or broken.