14-10-2016, 10:51 AM
(This post was last modified: 14-10-2016, 10:53 AM by Mike Watterson.)
From WWII onwards the headphone socket might have been for 200 to 600 Ohms.
Earlier sets with no loudspeaker, or a moving iron speaker (aka armature, Cone etc) used 2K to 4K. Older headphones are almost all 2K per earpiece wired in series. The only valve gear I've seen with a low impedance (i.e. will drive 8 to 32 Ohms) headphone socket is the 1950s Hallicrafters S72R. The manual actually recommends 500 Ohms to 5000 Ohms, but mine has the socket switching out the 3 Ohm loudspeaker.
My McMichael suitcase has the headphone socket between +120V HT and anode, this is normal from 1922 up to mid 1930s for any set without an output transformer to a dynamic (less than 16 Ohms voice coil) loudspeaker.
Modern 8 Ohms, 32 Ohms and 1928 4,000 Ohms earphones do work on the S72R!
Very few (any?) domestic sets from 1936 to 1960 with a low impedance speaker had a headphone socket at all. They seem to re-appear using 3.5mm or 2.5mm jacks on transistor sets, using a crystal earpiece in mid 1950s and miniature moving iron (metal disc) in 1960s. It's only with rare earth magnets you start to get miniature moving coil earpieces, the moving coil headphones before that were very large and heavy. Most WWII era 600 Ohm (approx) headphones, and maybe up to 1980s military are actually telephone handset inserts, which are just lower impedance versions of 1920s/1930s 2K + 2K headphones (all moving iron disc).
Earlier sets with no loudspeaker, or a moving iron speaker (aka armature, Cone etc) used 2K to 4K. Older headphones are almost all 2K per earpiece wired in series. The only valve gear I've seen with a low impedance (i.e. will drive 8 to 32 Ohms) headphone socket is the 1950s Hallicrafters S72R. The manual actually recommends 500 Ohms to 5000 Ohms, but mine has the socket switching out the 3 Ohm loudspeaker.
My McMichael suitcase has the headphone socket between +120V HT and anode, this is normal from 1922 up to mid 1930s for any set without an output transformer to a dynamic (less than 16 Ohms voice coil) loudspeaker.
Modern 8 Ohms, 32 Ohms and 1928 4,000 Ohms earphones do work on the S72R!
Very few (any?) domestic sets from 1936 to 1960 with a low impedance speaker had a headphone socket at all. They seem to re-appear using 3.5mm or 2.5mm jacks on transistor sets, using a crystal earpiece in mid 1950s and miniature moving iron (metal disc) in 1960s. It's only with rare earth magnets you start to get miniature moving coil earpieces, the moving coil headphones before that were very large and heavy. Most WWII era 600 Ohm (approx) headphones, and maybe up to 1980s military are actually telephone handset inserts, which are just lower impedance versions of 1920s/1930s 2K + 2K headphones (all moving iron disc).
