Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: clyde on April 18, 2024, 01:26:06 pm

Title: Jensen Field Coil Speaker
Post by: clyde on April 18, 2024, 01:26:06 pm

I have come into possession of a lovely old 12" speaker as above, 220 723, ST 174F12, SC4818.  It is 4 ohm impedance, a third wire (dummy coil?), a small mounted OPT, 196ohms, 175ohms each side of the primary.  The coil measures 2.4k which I find a challenge to incorporate into the power supply.  I have experience with field coils of much lower resistance used as chokes but this seems too high for that application.  Any suggestions?   

Title: Re: Jensen Field Coil Speaker
Post by: AlNewman on April 19, 2024, 01:17:53 pm

Sometimes they mounted the field coils direct to ground via the center tap, or off B+.  I've rebuilt a couple radios using that method.