I have a Zenith 12 tube speaker(12s265) that I would like to rewind. I have been doing research and found so many different ideas and procedures on figuring out what kind of wire and what size. I would like to rewind the original 670ohm field coil to approx 300ohms. I intend to use this 12" speaker in my 15 tube zenith(275ohm field coil). I know there is a significant current increase from the 12 tube to the 15 tube radio. I am concerned about the gauge of wire. What do you suggest using and how much wire? I am new to rewinding coils and there is almost no possibility of me finding the original speaker(Part number 49-187), that is why I want to rewind the coil.

Any thoughts are greatly appreciated!!!

I apologize, I ment that there is a small possibility of finding the original speaker...

Clair,
Wire sizing and number of turns etc is the easy part. Is the original power supply capable of the additional load, and if so, it might be simpler to parallel the field coil connections with the appropriate value of 10-20 watt resistor, unless you are an absolute purist.
Additionally, the resulting voltage can be higher with this reduction in resistance, and could affect capacitors beyond the field coil. I have the experience of only one field coil rewind, (about 15000 ft) but the experience is well documented.
marv
:I have a Zenith 12 tube speaker(12s265) that I would like to rewind. I have been doing research and found so many different ideas and procedures on figuring out what kind of wire and what size. I would like to rewind the original 670ohm field coil to approx 300ohms. I intend to use this 12" speaker in my 15 tube zenith(275ohm field coil). I know there is a significant current increase from the 12 tube to the 15 tube radio. I am concerned about the gauge of wire. What do you suggest using and how much wire? I am new to rewinding coils and there is almost no possibility of me finding the original speaker(Part number 49-187), that is why I want to rewind the coil.
:
:Any thoughts are greatly appreciated!!!

Clair,
Additionally the RC components before and after field coil are part of the power supply filtering (60/120 Hz), take care to not create another hum problem with this added load.
marv

:Clair,
:Wire sizing and number of turns etc is the easy part. Is the original power supply capable of the additional load, and if so, it might be simpler to parallel the field coil connections with the appropriate value of 10-20 watt resistor, unless you are an absolute purist.
:Additionally, the resulting voltage can be higher with this reduction in resistance, and could affect capacitors beyond the field coil. I have the experience of only one field coil rewind, (about 15000 ft) but the experience is well documented.
:marv
::I have a Zenith 12 tube speaker(12s265) that I would like to rewind. I have been doing research and found so many different ideas and procedures on figuring out what kind of wire and what size. I would like to rewind the original 670ohm field coil to approx 300ohms. I intend to use this 12" speaker in my 15 tube zenith(275ohm field coil). I know there is a significant current increase from the 12 tube to the 15 tube radio. I am concerned about the gauge of wire. What do you suggest using and how much wire? I am new to rewinding coils and there is almost no possibility of me finding the original speaker(Part number 49-187), that is why I want to rewind the coil.
::
::Any thoughts are greatly appreciated!!!

Note to Marv: The radio will not be affected by an increased load because there won't be an increased load. He is rewinding the speaker so that it can be used in a different radio that originally had a 275 ohm field coil. If his rewound coil has 300 ohms resistance, the power supply will perform exactly the same.

Placing a resistor in parallel with the original 600 ohm field coil is a great idea. It will eliminate a bothersome rewind. What must be done is the original voltage drop across the 600 ohm coil in its original radio must be established. The voltage created across the field is critical as it determines the amount of magnetism created by the field. Then what you do is place the speaker in the new 15 tube radio with a resistor in parallel with the field to creat roughly 275 or 300 ohms total resistance. After that measure the voltage across the field in the new radio with the resistor across it. Hopefully the voltage will be the same due to the higher current draw of a larger tube count radio. If it is lower, try increasing the resistance in parallel. It cannot be increased too much, as this will cut down on power available to the radio. Try to get both the voltage across the field and the voltages in the radio after the field to be correct. If this cannot be done, then the field coil must be rewound to 275-300 ohms.

Thomas

Thanks for the comments thus far! Placing a resistor in parallel or series to adjust the voltage is a wonderful idea, but it has one problem. My field coil is open. I tried the flashing method and I did get intermittent results, but not permenant. Once I get a field coil for the speaker working, I will tweek the voltages as needed with power resistors.

My first order of business is getting a working field coil speaker. Does anyone have any ideas or suggestions?

Ah. You didn't mention that it was open in your original posting. The resistor idea would only be practical if the 670 ohm field coil worked still. It would eliminate the need for a rewind. If the 670 ohm field coil is open, though, you are better off just winding it for 275 ohms and dropping the resistor idea.

Thomas

Sorry for the confusion.

Any thoughts on either rewinding or knowing anyone who is the best at doing this?

:Ah. You didn't mention that it was open in your original posting. The resistor idea would only be practical if the 670 ohm field coil worked still. It would eliminate the need for a rewind. If the 670 ohm field coil is open, though, you are better off just winding it for 275 ohms and dropping the resistor idea.
:
:Thomas

Thomas,
I lost it for a brief instant. Clair you can dismantle the electromagnet enclosure, unwind turns in hopes of finding only 1 break. If you find only 1 break before you reach the ultimate goal of 275 ohms, you're in luck, and a complete rewind is not required. If you can accurately measure the diameter of the wire or find its specs, its nominal current can be derived from reference data. If the 3 additional tubes in the new set are not power hungry audio circuits, existing wire should handle the load, otherwise a complete rewind with larger wire is in order. Obviously, the field magnetism and more current to throw a 15" speaker cone would be greater than a 12" I would expect some notable difference in the audio reproduction because of 12" cone resistance/spider mechanism/drivers vs the original 15" unit.
marv

:Ah. You didn't mention that it was open in your original posting. The resistor idea would only be practical if the 670 ohm field coil worked still. It would eliminate the need for a rewind. If the 670 ohm field coil is open, though, you are better off just winding it for 275 ohms and dropping the resistor idea.
:
:Thomas