Hello I have a Rogers De Forest Crosley "Kent" Model.
I normally am an amplifier "Tube" Guy but am trying to fix this radio for a friend. I had to replace every Cap and Resistor as they were way out.. So after that I went to bring it up carfully on a variac and the voltages especially the negative voltage from the center tap of the power tranny to the field coil seem wacked
the schem I am working on is here, http://www.nostalgiaair.org/RCC/Rogers%20Majestic/rogm007.gif
I have a question or suspicion about the plug in speaker assembly and have never worked with a speaker assembly like this with 3 coils (voice coil, field coil and output tranny). It says in the schematic that I should see -80 on pin 5 from the center tap of the power TX out to the field coil. I am measuring over
-300V at this point and all the other voltages seem low elseware in the radio. When I measured what I think is the field coil in the schem it says it is supposed to be (1000)ohms cold I measure 500M ohms.
Could someone please help me figure out if this speaker assembly is good or what measurements to take to prove? I thought maybee this hi negative voltage maybe due to this hi resistance reading on the field coil. That is of course if "it" the 1000 ohms can be measured using a DC volt meter.

Thanx Brian

Hi Brian

With those voltage and resistance readings the field is open. This is a common problem. If lucky, you may find a poor connection where leads meet the winding.

For a test, add a 1000 ohm 10 watt resistor across the field winding and see if voltages come up. This won't give much sound as a speaker needs the magnet. You might be able to attach a magnet to the speaker?

If you can't repair or find another speaker with a field you will need a permanent magnet type. The field can be replaced with a choke and/or wire wound resistor combination. If using a resistor alone you may need to increase filter cap values to eliminate hum.

Norm

: Hello I have a Rogers De Forest Crosley "Kent" Model.
: I normally am an amplifier "Tube" Guy but am trying to fix this radio for a friend. I had to replace every Cap and Resistor as they were way out.. So after that I went to bring it up carfully on a variac and the voltages especially the negative voltage from the center tap of the power tranny to the field coil seem wacked
: the schem I am working on is here, http://www.nostalgiaair.org/RCC/Rogers%20Majestic/rogm007.gif
: I have a question or suspicion about the plug in speaker assembly and have never worked with a speaker assembly like this with 3 coils (voice coil, field coil and output tranny). It says in the schematic that I should see -80 on pin 5 from the center tap of the power TX out to the field coil. I am measuring over
: -300V at this point and all the other voltages seem low elseware in the radio. When I measured what I think is the field coil in the schem it says it is supposed to be (1000)ohms cold I measure 500M ohms.
: Could someone please help me figure out if this speaker assembly is good or what measurements to take to prove? I thought maybee this hi negative voltage maybe due to this hi resistance reading on the field coil. That is of course if "it" the 1000 ohms can be measured using a DC volt meter.

: Thanx Brian

Norm thanx as always,,, I will try just that and I appreciate the info....Brian

: Hi Brian

: With those voltage and resistance readings the field is open. This is a common problem. If lucky, you may find a poor connection where leads meet the winding.

: For a test, add a 1000 ohm 10 watt resistor across the field winding and see if voltages come up. This won't give much sound as a speaker needs the magnet. You might be able to attach a magnet to the speaker?

: If you can't repair or find another speaker with a field you will need a permanent magnet type. The field can be replaced with a choke and/or wire wound resistor combination. If using a resistor alone you may need to increase filter cap values to eliminate hum.

: Norm

: : Hello I have a Rogers De Forest Crosley "Kent" Model.
: : I normally am an amplifier "Tube" Guy but am trying to fix this radio for a friend. I had to replace every Cap and Resistor as they were way out.. So after that I went to bring it up carfully on a variac and the voltages especially the negative voltage from the center tap of the power tranny to the field coil seem wacked
: : the schem I am working on is here, http://www.nostalgiaair.org/RCC/Rogers%20Majestic/rogm007.gif
: : I have a question or suspicion about the plug in speaker assembly and have never worked with a speaker assembly like this with 3 coils (voice coil, field coil and output tranny). It says in the schematic that I should see -80 on pin 5 from the center tap of the power TX out to the field coil. I am measuring over
: : -300V at this point and all the other voltages seem low elseware in the radio. When I measured what I think is the field coil in the schem it says it is supposed to be (1000)ohms cold I measure 500M ohms.
: : Could someone please help me figure out if this speaker assembly is good or what measurements to take to prove? I thought maybee this hi negative voltage maybe due to this hi resistance reading on the field coil. That is of course if "it" the 1000 ohms can be measured using a DC volt meter.

: : Thanx Brian

Thanx Norm and Dr.T i peeled off the layer of paper and sur enough
there was a burn mark and it was open so I peeled it back a bit
and measured 1000 ohms and reattached the wire.. Thanx guys..
Glad to have a place to come other wise I may never figure
these things out not that I'm dumb but As the way they did things of old
are to me sometimes unfamiliar

: Norm thanx as always,,, I will try just that and I appreciate the info....Brian

:
: : Hi Brian

: : With those voltage and resistance readings the field is open. This is a common problem. If lucky, you may find a poor connection where leads meet the winding.

: : For a test, add a 1000 ohm 10 watt resistor across the field winding and see if voltages come up. This won't give much sound as a speaker needs the magnet. You might be able to attach a magnet to the speaker?

: : If you can't repair or find another speaker with a field you will need a permanent magnet type. The field can be replaced with a choke and/or wire wound resistor combination. If using a resistor alone you may need to increase filter cap values to eliminate hum.

: : Norm

: : : Hello I have a Rogers De Forest Crosley "Kent" Model.
: : : I normally am an amplifier "Tube" Guy but am trying to fix this radio for a friend. I had to replace every Cap and Resistor as they were way out.. So after that I went to bring it up carfully on a variac and the voltages especially the negative voltage from the center tap of the power tranny to the field coil seem wacked
: : : the schem I am working on is here, http://www.nostalgiaair.org/RCC/Rogers%20Majestic/rogm007.gif
: : : I have a question or suspicion about the plug in speaker assembly and have never worked with a speaker assembly like this with 3 coils (voice coil, field coil and output tranny). It says in the schematic that I should see -80 on pin 5 from the center tap of the power TX out to the field coil. I am measuring over
: : : -300V at this point and all the other voltages seem low elseware in the radio. When I measured what I think is the field coil in the schem it says it is supposed to be (1000)ohms cold I measure 500M ohms.
: : : Could someone please help me figure out if this speaker assembly is good or what measurements to take to prove? I thought maybee this hi negative voltage maybe due to this hi resistance reading on the field coil. That is of course if "it" the 1000 ohms can be measured using a DC volt meter.

: : : Thanx Brian