I have the chasis of a Fairbanks Morse 8A, with no speaker and no cabinet (it was a freebie). I am going to try using a permanent magnet speaker by replacing the speaker field coil with a resistor and using the PM magnet. BUT, the schematic I see on Nost Air seems to show the field coil as 1K (HOT) using the standard ohm symbol for that specification only. All of the other resistors are using the older symbol that looks like a small w. The field could be saying 10,000, not 1000 ohm, it's hard to tell. Does anyone have a clear schematic or the knowledge of what the field resistence actually is?

It would be very unlikely to be 10k.
1k is closer to typical

:It would be very unlikely to be 10k.
:1k is closer to typical
:

Another logical way to look at it that a typical B+ current is about 60 to 80 ma.

So a 1k resistor would drop about 60-80 volts which is a reasonable amount to drop.

But a 10k would drop 600-800 volts. That's WAY more voltage than you have available at the rectifier.

Agree with Peter. This radio uses a 1,000 ohm field coil:

http://www.nostalgiaair.org/PagesByModel/757/M0005757.pdf

Resistance should be kept fairly close to this value. The field is in negative side of power supply and is used to set up bias voltages for tubes.

Norm

::It would be very unlikely to be 10k.
::1k is closer to typical
::
:
:Another logical way to look at it that a typical B+ current is about 60 to 80 ma.
:
:So a 1k resistor would drop about 60-80 volts which is a reasonable amount to drop.
:
:But a 10k would drop 600-800 volts. That's WAY more voltage than you have available at the rectifier.
:

Thanks to all, I tried a 1K 5W resistor and it got hotter than I liked, but will just go to ten watts and cross my fingers. I don't have to make this one work, but I see it as a learning opportunity and you guys have given me a new way to look at the circuit.

:Agree with Peter. This radio uses a 1,000 ohm field coil:
:
:http://www.nostalgiaair.org/PagesByModel/757/M0005757.pdf
:
:Resistance should be kept fairly close to this value. The field is in negative side of power supply and is used to set up bias voltages for tubes.
:
:Norm
:
:::It would be very unlikely to be 10k.
:::1k is closer to typical
:::
::
::Another logical way to look at it that a typical B+ current is about 60 to 80 ma.
::
::So a 1k resistor would drop about 60-80 volts which is a reasonable amount to drop.
::
::But a 10k would drop 600-800 volts. That's WAY more voltage than you have available at the rectifier.
::
:
:

:Thanks to all, I tried a 1K 5W resistor and it got hotter than I liked, but will just go to ten watts and cross my fingers. I don't have to make this one work, but I see it as a learning opportunity and you guys have given me a new way to look at the circuit.
:

Assuming your B+ draws 70ma for example:
A 1k resistor will drop 70v
and to calculate wattage
P= IxE
Power= .07a x 70v = 4.9watts (tripled for safety) = 15 watt resistor.

::Thanks to all, I tried a 1K 5W resistor and it got hotter than I liked, but will just go to ten watts and cross my fingers. I don't have to make this one work, but I see it as a learning opportunity and you guys have given me a new way to look at the circuit.
::
:
:Assuming your B+ draws 70ma for example:
:A 1k resistor will drop 70v
:and to calculate wattage
:P= IxE
:Power= .07a x 70v = 4.9watts (tripled for safety) = 15 watt resistor.
:
:
Now that was a fun experience, I replaced 3 tubes, 2 resistors, worked around the field coil, and added a permanent magnet speaker. Not so unusual, but the interesting point is that it sounds great and I didn't replace a single cap anywhere. Now I have to rebuild a cabinet from just a few pieces. Thanks again, it was a ball.

If you have not replaced any of the capacitors yet...
You should replace the electrolytic filter caps for sure.
And also ALL paper caps.
Check all resistor for value +/- 20% and replace any out of that range.

:If you have not replaced any of the capacitors yet...
:You should replace the electrolytic filter caps for sure.
:And also ALL paper caps.
:Check all resistor for value +/- 20% and replace any out of that range.
:
:
I have not yet done the caps, but yes, am familiar with the wisdom of replacing the filters and paper caps, as well as the agony of wishing I had on past radios. But, boy can that be a learning experience. I will also the resistors as needed.

Great.
Good luck with the 8A ... Seems Fairbanks Morse radios are very desirable.