# how to drive 1930s bakelite headphones

I’ve received a very old pair of mono bakelite headphones that I would like to re-use for demonstration purposes. Just for voice audio and morse code tones.

The writings on the side of each headphone:

SB & CO
C.L.R.
1939


This leads me to believe it’s a C-type unit (whatever that means) with Low Resistance (Impedance) from the year 1939. The DC resistance I measured is around 62 Ohms for each headphone and there are no shorts or open circuits. The two earpieces are connected in series and each earpiece has two coils below a thin metal disc.

Image 1: inside closeup of headphone coils (disc removed)

Image 2: wiring

What would be the ideal or maximum signal levels can I drive these headphones with, and what sort of pre-amplifier would I need to make these headphones produce the best possible (probably still awful) sound when driven from a laptop or radio's headphone socket?

Is this where I need to dig up and replicate an old, valve radio's audio output stage? I am hoping to do this with slightly more modern components..

• These headphones should be compatible with any device that can drive ear-buds, or drive a loudspeaker. Except that hard bakelite against your ears can be painful after awhile. Be aware that the small hole in the bakelite cap forms an audio resonant cavity that probably has a peak below 1 kHz. Not ideal for music, but quite acceptable for voice. – glen_geek Nov 13 '17 at 16:57
• I had no idea that these headphones would be so sensitive. I will hook up some leads and a connector and try it out. It's definitely not for long-term listening but the headphones look in a reasonably good state and I'm just very intrigued as to how they might sound almost 80 years later.. – captcha Nov 13 '17 at 21:32
• As a side note, they can function as a mic too. Also as a sensitive magnetic pickup by removing the steel diaphragm and placing them against a magnetic surface and amplifying the output. That reduces most feedback, allowing very high amplification. I used a pair long ago on an old metal fire safe. – Optionparty Nov 14 '17 at 3:36
• Hehe, the possibilities are endless! Thanks everyone for their excellent feedback. I've accepted Bimpelrekkie's answer, who not only provided a lot of additional information but also responded to my question with 10 minutes of my asking. SE is awesome. – captcha Nov 14 '17 at 9:11