Electrodynamic to Permanent Magnet Speaker conversion
« on: September 15, 2007, 04:12:13 PM »
Is there anything other than the absence (or because of the absence) of the field coil in a permanent magnet speaker that has to be taken in consideration when attaching to an amp (quad 6v6 PP) designed for electrodynamics?


Choke and dcr
« Reply #1 on: September 15, 2007, 04:26:36 PM »
The field coil was usually used in the power supply as a choke.  So it you replace the speaker with a pm speaker you need to replace the coil with a resistor of the same dcr or the combo of a choke and resistor equaling the same dcr.  I have also seen the coil used on the ground side with the power tube bias taken from the neg end of the coil.  It's usually relatively straightforward to make the swap, but you should be somewhat familiar with the circuit.



Electrodynamic to Permanent Magnet Speaker conversion
« Reply #2 on: September 18, 2007, 09:22:22 AM »
I would use an actual choke and not dissipate all the power as heat.


Electrodynamic to Permanent Magnet Speaker conversion
« Reply #3 on: September 19, 2007, 09:58:10 PM »
I am currently opting to re-cone any blown field-coil speakers.  A good craftsman can make a full kit from parts as they are still available.  

I have thought about NOS Alnico replacements, and if I were to do it, I would use only a choke as a replacement for the field coil in the power supply.  Another idea would be to remove the coil from the basket, if the situation was a total loss, and still use the same exact choke.  I have never had a bad field coil yet- only voice coils, surrounds, cones, spiders, etc.