Hello, I have replaced the feild coil speaker with a pm type and have subbed the field coil with a 500ohm 10 watt resistor, the radio sounds great with plenty of volume, the only problem is that there is some hum that wasn't there before, only noticeable when volume is low, I would have kept the field coil in the circuit rather than using a resitor, just no room on the chassis, anny other tricks to get rid of the hum?

Try adding an additional 10 mf filter capacitor AFTER the power resistor you have subbed in. Careful on the polarity!.

Hello, I have replaced the feild coil speaker with a pm type and have subbed the field coil with a 500ohm 10 watt resistor, the radio sounds great with plenty of volume, the only problem is that there is some hum that wasn't there before, only noticeable when volume is low, I would have kept the field coil in the circuit rather than using a resitor, just no room on the chassis, anny other tricks to get rid of the hum?
:

:Try adding an additional 10 mf filter capacitor AFTER the power resistor you have subbed in. Careful on the polarity!.
:
:Hello, I have replaced the feild coil speaker with a pm type and have subbed the field coil with a 500ohm 10 watt resistor, the radio sounds great with plenty of volume, the only problem is that there is some hum that wasn't there before, only noticeable when volume is low, I would have kept the field coil in the circuit rather than using a resitor, just no room on the chassis, anny other tricks to get rid of the hum?
::
:
If it was removable, I would have kept the field coil in the circuit and, if possible. mounted it somewhere else in the cabinet. I have done this before. Although it is possible to replace a field coil with a resistor and capacitor, I never do. The field coil provides an inductance, not a resistance. There is a great difference between the two. I don't know the theory, which has to do with leading and retarded voltages, but I know that there IS an electrical difference. An inductor develops a magnetic field which allows the voltage to rise over a period of time, not instantaneously as in a resistor. It's true that a capacitor acts in a similar, but not exact, way.
I would suggest looking up "Inductor theory" on the internet to better understand this effect.
Terry

Agreed, the field coil was an elegant efficient method of creating a magnetic field before the widespread availability of ALNICO magnets existed and furthermore provided a relatively waste free and smoothing of the DC supply with minimal use of relatively expensive capacitors of the day.

Of course, if you can find a replacement speaker that would be nice.

That being said, try to emulate the old circuit at least resistance wise and you can ramp up down hill capacitors as needed to get the hum under control.

::Try adding an additional 10 mf filter capacitor AFTER the power resistor you have subbed in. Careful on the polarity!.
::
::Hello, I have replaced the feild coil speaker with a pm type and have subbed the field coil with a 500ohm 10 watt resistor, the radio sounds great with plenty of volume, the only problem is that there is some hum that wasn't there before, only noticeable when volume is low, I would have kept the field coil in the circuit rather than using a resitor, just no room on the chassis, anny other tricks to get rid of the hum?
:::
::
:If it was removable, I would have kept the field coil in the circuit and, if possible. mounted it somewhere else in the cabinet. I have done this before. Although it is possible to replace a field coil with a resistor and capacitor, I never do. The field coil provides an inductance, not a resistance. There is a great difference between the two. I don't know the theory, which has to do with leading and retarded voltages, but I know that there IS an electrical difference. An inductor develops a magnetic field which allows the voltage to rise over a period of time, not instantaneously as in a resistor. It's true that a capacitor acts in a similar, but not exact, way.
:I would suggest looking up "Inductor theory" on the internet to better understand this effect.
:Terry
:

:Agreed, the field coil was an elegant efficient method of creating a magnetic field before the widespread availability of ALNICO magnets existed and furthermore provided a relatively waste free and smoothing of the DC supply with minimal use of relatively expensive capacitors of the day.
:
:Of course, if you can find a replacement speaker that would be nice.
:
:That being said, try to emulate the old circuit at least resistance wise and you can ramp up down hill capacitors as needed to get the hum under control.
:
:::Try adding an additional 10 mf filter capacitor AFTER the power resistor you have subbed in. Careful on the polarity!.
:::
:::Hello, I have replaced the feild coil speaker with a pm type and have subbed the field coil with a 500ohm 10 watt resistor, the radio sounds great with plenty of volume, the only problem is that there is some hum that wasn't there before, only noticeable when volume is low, I would have kept the field coil in the circuit rather than using a resitor, just no room on the chassis, anny other tricks to get rid of the hum?
::::
:::
::If it was removable, I would have kept the field coil in the circuit and, if possible. mounted it somewhere else in the cabinet. I have done this before. Although it is possible to replace a field coil with a resistor and capacitor, I never do. The field coil provides an inductance, not a resistance. There is a great difference between the two. I don't know the theory, which has to do with leading and retarded voltages, but I know that there IS an electrical difference. An inductor develops a magnetic field which allows the voltage to rise over a period of time, not instantaneously as in a resistor. It's true that a capacitor acts in a similar, but not exact, way.
::I would suggest looking up "Inductor theory" on the internet to better understand this effect.
::Terry
::
:
:
I have kept the field coil and centre yoke, however I used the old speaker frame to make a mounting bracket for the pm speaker, I think that I will try and find a way and spot to mount field coil, the only part lost is the hum coil but that should be easy to replicate with some magnet wire and there was only a couple of turns, I know the feild coil acts as a choke, the same as some ac/dc radio's that have pm mag speaker and a seperate choke. Thanxs for the info Guy's.