1. All that the service informations says about the speaker field is that it is 1,600 ohms. Would a different size filter choke work better than the one I installed?
2. Should I unhook the wires to the speaker field?
3. Why does the speaker work. I thought the speaker field created an electromagnet for the speaker, which was necessary for it to function.
Thanks in advance for your thoughts.
You can replace the speaker with another electrodynmic or with a modern permanent magnet speaker.
If you go with a PM speaker, leave the 5-H choke in the B+ ckt, and add a series power resistor to bring the total DC reistance up to 1.6K.
It seems like your 50-mA choke should be OK for the plate supply. Check to make sure it's not getting overly hot.
:Finally got a 1936 Arvin model 518 working. The biggest hurdle for me was figuring out that the speaker field, which also serves as part of the power supply filter, doesn't work. I happened to have a 5 henry, 50 Ma filter choke in the drawer, so I wired it into the circuit. I did not unhook the speaker field wires. The radio came alive, though it's a little fuzzy. I have three questions:
:
:1. All that the service informations says about the speaker field is that it is 1,600 ohms. Would a different size filter choke work better than the one I installed?
:
:2. Should I unhook the wires to the speaker field?
:
:3. Why does the speaker work. I thought the speaker field created an electromagnet for the speaker, which was necessary for it to function.
:
:Thanks in advance for your thoughts.
Residual magnetism?.... humm where would that be coming from Doug?
Do you mean that after a while the field coil sort of magnetized the sourrounding metal berfore it died... and now that's acting like a PM speaker?
Guys,
Before I completely write off the speaker, I would check the connections of the field coil magnet wire and the lead to the radio to see if there is a bad connection. May find a broken or corroded in to connection in the outer turns of the coil.
Radiodoc
::Is the field coil open or not? If it IS open... I don't understand how the speaker would work either.
::
::Residual magnetism?.... humm where would that be coming from Doug?
::Do you mean that after a while the field coil sort of magnetized the sourrounding metal berfore it died... and now that's acting like a PM speaker?
:
:Guys,
:
:Before I completely write off the speaker, I would check the connections of the field coil magnet wire and the lead to the radio to see if there is a bad connection. May find a broken or corroded in to connection in the outer turns of the coil.
:
:Radiodoc
:
The field coil supplies B+ to your radio. You can bypass an open field with a choke but should also add some series resistance. Need a wire wound resistor for this. A choke will have lower DC resistance than the field. This will give higher voltage and the radio will draw more current. More current might be what is causing overheating of the power transformer?
Have you replaced filter caps? Other caps may also be leaky and can cause higher current to be drawn and a distorted sound.
Your speaker will need to be replaced unless the field winding can be repaired. Might be able to attach a strong magnet to the speaker to make a magnetic field? Computer hard drives have strong magnets.
Norm
:The odd thing is that I get no b+ through the field coil. If I bypass it with a choke I do get b+, and the radio begins to work, though not great. The fact that b+ is dead through the speaker field was telling me that the coil is open. But, meanwhile, it's true that the speaker works. I have noticed that the power transformer is getting hot, which is troublesom. I'm hoping that stops if I unhook the speaker coil.
:
:::Is the field coil open or not? If it IS open... I don't understand how the speaker would work either.
:::
:::Residual magnetism?.... humm where would that be coming from Doug?
:::Do you mean that after a while the field coil sort of magnetized the sourrounding metal berfore it died... and now that's acting like a PM speaker?
::
::Guys,
::
::Before I completely write off the speaker, I would check the connections of the field coil magnet wire and the lead to the radio to see if there is a bad connection. May find a broken or corroded in to connection in the outer turns of the coil.
::
::Radiodoc
::
Try pulling the rectifier tube (80) and turn on the radio for several minutes and see if the transformer gets hot. As Norm mentioned, have you replaced the electrolytic caps in the power supply circuit? Possibly may have been a bad one which caused the field coil to open.
Radiodoc
:Hi Mike
:
: The field coil supplies B+ to your radio. You can bypass an open field with a choke but should also add some series resistance. Need a wire wound resistor for this. A choke will have lower DC resistance than the field. This will give higher voltage and the radio will draw more current. More current might be what is causing overheating of the power transformer?
:
: Have you replaced filter caps? Other caps may also be leaky and can cause higher current to be drawn and a distorted sound.
:
: Your speaker will need to be replaced unless the field winding can be repaired. Might be able to attach a strong magnet to the speaker to make a magnetic field? Computer hard drives have strong magnets.
:
:Norm
:
::The odd thing is that I get no b+ through the field coil. If I bypass it with a choke I do get b+, and the radio begins to work, though not great. The fact that b+ is dead through the speaker field was telling me that the coil is open. But, meanwhile, it's true that the speaker works. I have noticed that the power transformer is getting hot, which is troublesom. I'm hoping that stops if I unhook the speaker coil.
::
::::Is the field coil open or not? If it IS open... I don't understand how the speaker would work either.
::::
::::Residual magnetism?.... humm where would that be coming from Doug?
::::Do you mean that after a while the field coil sort of magnetized the sourrounding metal berfore it died... and now that's acting like a PM speaker?
:::
:::Guys,
:::
:::Before I completely write off the speaker, I would check the connections of the field coil magnet wire and the lead to the radio to see if there is a bad connection. May find a broken or corroded in to connection in the outer turns of the coil.
:::
:::Radiodoc
:::
Is 50ma enough for the Choke? I kinda doubt it.
:
:
:
:
::Hi Mike
::
:: The field coil supplies B+ to your radio. You can bypass an open field with a choke but should also add some series resistance. Need a wire wound resistor for this. A choke will have lower DC resistance than the field. This will give higher voltage and the radio will draw more current. More current might be what is causing overheating of the power transformer?
::
:: Have you replaced filter caps? Other caps may also be leaky and can cause higher current to be drawn and a distorted sound.
::
:: Your speaker will need to be replaced unless the field winding can be repaired. Might be able to attach a strong magnet to the speaker to make a magnetic field? Computer hard drives have strong magnets.
::
::Norm
::
:::The odd thing is that I get no b+ through the field coil. If I bypass it with a choke I do get b+, and the radio begins to work, though not great. The fact that b+ is dead through the speaker field was telling me that the coil is open. But, meanwhile, it's true that the speaker works. I have noticed that the power transformer is getting hot, which is troublesom. I'm hoping that stops if I unhook the speaker coil.
:::
:::::Is the field coil open or not? If it IS open... I don't understand how the speaker would work either.
:::::
:::::Residual magnetism?.... humm where would that be coming from Doug?
:::::Do you mean that after a while the field coil sort of magnetized the sourrounding metal berfore it died... and now that's acting like a PM speaker?
::::
::::Guys,
::::
::::Before I completely write off the speaker, I would check the connections of the field coil magnet wire and the lead to the radio to see if there is a bad connection. May find a broken or corroded in to connection in the outer turns of the coil.
::::
::::Radiodoc
::::
:Mike,
:
:Try pulling the rectifier tube (80) and turn on the radio for several minutes and see if the transformer gets hot. As Norm mentioned, have you replaced the electrolytic caps in the power supply circuit? Possibly may have been a bad one which caused the field coil to open.
:
:Radiodoc
:
:
:
:
::Hi Mike
::
:: The field coil supplies B+ to your radio. You can bypass an open field with a choke but should also add some series resistance. Need a wire wound resistor for this. A choke will have lower DC resistance than the field. This will give higher voltage and the radio will draw more current. More current might be what is causing overheating of the power transformer?
::
:: Have you replaced filter caps? Other caps may also be leaky and can cause higher current to be drawn and a distorted sound.
::
:: Your speaker will need to be replaced unless the field winding can be repaired. Might be able to attach a strong magnet to the speaker to make a magnetic field? Computer hard drives have strong magnets.
::
::Norm
::
:::The odd thing is that I get no b+ through the field coil. If I bypass it with a choke I do get b+, and the radio begins to work, though not great. The fact that b+ is dead through the speaker field was telling me that the coil is open. But, meanwhile, it's true that the speaker works. I have noticed that the power transformer is getting hot, which is troublesom. I'm hoping that stops if I unhook the speaker coil.
:::
:::::Is the field coil open or not? If it IS open... I don't understand how the speaker would work either.
:::::
:::::Residual magnetism?.... humm where would that be coming from Doug?
:::::Do you mean that after a while the field coil sort of magnetized the sourrounding metal berfore it died... and now that's acting like a PM speaker?
::::
::::Guys,
::::
::::Before I completely write off the speaker, I would check the connections of the field coil magnet wire and the lead to the radio to see if there is a bad connection. May find a broken or corroded in to connection in the outer turns of the coil.
::::
::::Radiodoc
::::
If you have a voltohm meter, measure the resistance of the choke coil disconnected from the circuit and subtract that from the resistance value (1600) of the field coil to determine the value of the series resistor that will be needed to replace the field coil. An example would be the choke coil measured 100 ohms. You would then need a 1500 ohm resistor in series at probably 10 to 20 watts. Another note about the power supply is C12's negative lead does not connect to the chassis but to the power transformer's high voltage centertap. Make sure if the old cap is left mounted that you isolate the new cap connections from the old cap connections.
Radiodoc
Radiodoc
:
:Yes, I have replaced the filter caps, but the old ones were originals and the damage was probably already done. I'll take out the 80 and check out what happens to the transformer this evening. The choke is 5 henry, 50 Ma, any thoughts on what size wire wound resistor would be appropriate to bring resistance up to 1.6 K ohms - the rating of the speaker field? Could I figure it out by testing the resistance of the choke and simply adding the right size resistor?
:
::Mike,
::
::Try pulling the rectifier tube (80) and turn on the radio for several minutes and see if the transformer gets hot. As Norm mentioned, have you replaced the electrolytic caps in the power supply circuit? Possibly may have been a bad one which caused the field coil to open.
::
::Radiodoc
::
::
::
::
:::Hi Mike
:::
::: The field coil supplies B+ to your radio. You can bypass an open field with a choke but should also add some series resistance. Need a wire wound resistor for this. A choke will have lower DC resistance than the field. This will give higher voltage and the radio will draw more current. More current might be what is causing overheating of the power transformer?
:::
::: Have you replaced filter caps? Other caps may also be leaky and can cause higher current to be drawn and a distorted sound.
:::
::: Your speaker will need to be replaced unless the field winding can be repaired. Might be able to attach a strong magnet to the speaker to make a magnetic field? Computer hard drives have strong magnets.
:::
:::Norm
:::
::::The odd thing is that I get no b+ through the field coil. If I bypass it with a choke I do get b+, and the radio begins to work, though not great. The fact that b+ is dead through the speaker field was telling me that the coil is open. But, meanwhile, it's true that the speaker works. I have noticed that the power transformer is getting hot, which is troublesom. I'm hoping that stops if I unhook the speaker coil.
::::
::::::Is the field coil open or not? If it IS open... I don't understand how the speaker would work either.
::::::
::::::Residual magnetism?.... humm where would that be coming from Doug?
::::::Do you mean that after a while the field coil sort of magnetized the sourrounding metal berfore it died... and now that's acting like a PM speaker?
:::::
:::::Guys,
:::::
:::::Before I completely write off the speaker, I would check the connections of the field coil magnet wire and the lead to the radio to see if there is a bad connection. May find a broken or corroded in to connection in the outer turns of the coil.
:::::
:::::Radiodoc
:::::
Peter,
If the field coil IS really open, then there must be some residual magnetism in the iron/steel pole pieces. I am pretty sure the volume would not be very loud though.
Radiodoc
Peter,
Want to hear a wild theory (possible but not probable)? What if the field coil winding shorted within a few turns of the load side and at this point the wire burned open opening the circuit from that point to the load side of the power supply and the other piece of wire shorted to the speaker frame grounded to the chassis. The part of the winding from the rectifier to the point of the short would have current flowing creating a magnetic field for the speaker. Placing a choke across the field coil leads would apply voltage to the radio.
Radiodoc
We definitely should be doing things in an orderly fashion here, though. If the radio sounds fuzzy, a new speaker should be used for the testing to elminate problems with the lack of a field. Fuzzy might be caused by bad condensers throughout the radio. There was talk about possible damage being done by the old electrolytics to the field coil and possibly the transformer. Old radios should never be turned on until all components have been tested and faulty ones have been replaced. Until all faulty components (namely condensers) have been located and replaced, no further work should be done to this radio with the power on. Using the radio as a test bench is poor practice. It is common knowledge that condensers leak and short out. Using the radio to find each one is a waste of time and a risk to the radio. I am surprised that more people on here who offer assistance do not strictly enforce this point. The very first step in this radio restoration, then, should be replacing all faulty, if not all, whether faulty or not faulty, condensers. Then move on to drifted resistors and bad wiring, and then try tubes for duds and shorts (though it is evident that the tubes are working). Then turn on the radio and see what happens.
Also, unless you feel like mounting the choke somewhere on the radio, you will probably get by just fine without it. Try operating the radio with a 1500 ohm resistor (assuming that your choke has a DC resistance of 100 ohms), capable of about 15 watts. If the radio hums excessively with only the resistor, and you are sure that all other faulty components have been replaced, and are in fine working order, then add the choke. The choke is a good idea, but isn't absolutely necessary in all cases. Try first without it. Idealy, if hum is a problem, you should obtain a replacement electrodynamic speaker, or have the field coil of the original one mended, as an electrodynamic speaker is the only perfect solution to hum problems, seeing as it has hum bucking devices built into it. If the resistor won't work by itself, though, the choke will probably do the trick in many cases.
Thomas
Thomas: He did replace the filter caps...
There was one reply pointing out that he should be careful about cap connections to chassis vs CT winding...
Still waiting to hear answer to that.
T.
1. Someone mentioned checking the continuity of the field coil. My volt/ohm meter has a feature that beeps when there is continuity. A piece of wire would make it beep, for example. It does not beep when I connect it to the two sides of the speaker field. Does that mean the field is open? I notice that it does not beep when I the meter probes are connected to both sides of the new choke I installed, which works fine. I don't understand that - inductance maybe? So, is there another way to check the continuity of the speaker field coil?
2. I notice that the speaker field has a third wire that is not on the schematic and never seems to have been used. It was wrapped neatly around the oustise of the speaker coil and tied down. What do you suppose that wire is? An unsused center tap?
Thanks for all your thoughts.
One other thing: Thanks for the note about the grounding of the electrolytics. I had both grounded to the centertap of the power transformer. One is supposed to go to the chassis. I'll fix that this weekend.
2.
I know he replaced the filter condensers, but I wonder if he replaced the rest of the condensers.
:
:T.
Mike,
You got me to thinking about one of my voltohms that has a continuity position. I tried it on various resistances and it would beep up to about 50 ohms resistance and only read out the resistance after that.
Radiodoc
Your volt/ohm meter can measure resistance. Set it to an ohms scale and see what you read. Most fields will be in the 1,000 ohm area. You can test a field by measuring voltage or even checking for a magnetic field. With the field under power core of a speaker is magnetized.
Some fields did have a tap. These were used in the negative side of a power supply and gave bias to the output tube. If you find a wire taped off probably a replaced speaker.
Norm
:Yes, first thing I did was replace all condensers and most resistors. Last night I took out the 80 and let it run for a while. The power transformer stayed cool - thankfully. Here are a couple more questions, though:
:
:1. Someone mentioned checking the continuity of the field coil. My volt/ohm meter has a feature that beeps when there is continuity. A piece of wire would make it beep, for example. It does not beep when I connect it to the two sides of the speaker field. Does that mean the field is open? I notice that it does not beep when I the meter probes are connected to both sides of the new choke I installed, which works fine. I don't understand that - inductance maybe? So, is there another way to check the continuity of the speaker field coil?
:
:2. I notice that the speaker field has a third wire that is not on the schematic and never seems to have been used. It was wrapped neatly around the oustise of the speaker coil and tied down. What do you suppose that wire is? An unsused center tap?
:
:Thanks for all your thoughts.
:
:One other thing: Thanks for the note about the grounding of the electrolytics. I had both grounded to the centertap of the power transformer. One is supposed to go to the chassis. I'll fix that this weekend.
:
:2.
:
:I know he replaced the filter condensers, but I wonder if he replaced the rest of the condensers.
::
::T.
:Hi Mike
:
: Your volt/ohm meter can measure resistance. Set it to an ohms scale and see what you read. Most fields will be in the 1,000 ohm area. You can test a field by measuring voltage or even checking for a magnetic field. With the field under power core of a speaker is magnetized.
:
: Some fields did have a tap. These were used in the negative side of a power supply and gave bias to the output tube. If you find a wire taped off probably a replaced speaker.
:
:Norm
:
::Yes, first thing I did was replace all condensers and most resistors. Last night I took out the 80 and let it run for a while. The power transformer stayed cool - thankfully. Here are a couple more questions, though:
::
::1. Someone mentioned checking the continuity of the field coil. My volt/ohm meter has a feature that beeps when there is continuity. A piece of wire would make it beep, for example. It does not beep when I connect it to the two sides of the speaker field. Does that mean the field is open? I notice that it does not beep when I the meter probes are connected to both sides of the new choke I installed, which works fine. I don't understand that - inductance maybe? So, is there another way to check the continuity of the speaker field coil?
::
::2. I notice that the speaker field has a third wire that is not on the schematic and never seems to have been used. It was wrapped neatly around the oustise of the speaker coil and tied down. What do you suppose that wire is? An unsused center tap?
::
::Thanks for all your thoughts.
::
::One other thing: Thanks for the note about the grounding of the electrolytics. I had both grounded to the centertap of the power transformer. One is supposed to go to the chassis. I'll fix that this weekend.
::
::2.
::
::I know he replaced the filter condensers, but I wonder if he replaced the rest of the condensers.
:::
:::T.
Resistance in the field will go up as the unit heats up, 1000 ohms or more is probably good. If the unit is bad it probably won't be close to 1600 at all.
David
:Thanks Norm. The speaker field is supposed to measure 1,600 ohms, according to service papers. Can I assume that a 1,600 ohm reading means the field is OK? What kind of ohms reading would say that it's bad?
:
::Hi Mike
::
:: Your volt/ohm meter can measure resistance. Set it to an ohms scale and see what you read. Most fields will be in the 1,000 ohm area. You can test a field by measuring voltage or even checking for a magnetic field. With the field under power core of a speaker is magnetized.
::
:: Some fields did have a tap. These were used in the negative side of a power supply and gave bias to the output tube. If you find a wire taped off probably a replaced speaker.
::
::Norm
::
:::Yes, first thing I did was replace all condensers and most resistors. Last night I took out the 80 and let it run for a while. The power transformer stayed cool - thankfully. Here are a couple more questions, though:
:::
:::1. Someone mentioned checking the continuity of the field coil. My volt/ohm meter has a feature that beeps when there is continuity. A piece of wire would make it beep, for example. It does not beep when I connect it to the two sides of the speaker field. Does that mean the field is open? I notice that it does not beep when I the meter probes are connected to both sides of the new choke I installed, which works fine. I don't understand that - inductance maybe? So, is there another way to check the continuity of the speaker field coil?
:::
:::2. I notice that the speaker field has a third wire that is not on the schematic and never seems to have been used. It was wrapped neatly around the oustise of the speaker coil and tied down. What do you suppose that wire is? An unsused center tap?
:::
:::Thanks for all your thoughts.
:::
:::One other thing: Thanks for the note about the grounding of the electrolytics. I had both grounded to the centertap of the power transformer. One is supposed to go to the chassis. I'll fix that this weekend.
:::
:::2.
:::
:::I know he replaced the filter condensers, but I wonder if he replaced the rest of the condensers.
::::
::::T.
T.
This radio does use a hum bucking coil, it also has a tapped field coil with one wire to the 80, one to the plate of the output tube and one for the B+. See Riders 8-10. Try Playthings of the Past for a transformer.
Dave
_______________________________________________________
Riders volume 8, Noblitt Sparks Industries (Arvin), page 10
Dave
I don't even what I just said...lol
Yes, I assume that you all understand Spanish.
¿Usted asume que entendemos español?
You assume that we understand Spanish?
::If there is no other evidence of a hum bucking coil, the wire wrapped around, if wrapped around about 10 to 20 times, is probably the hum bucking coil, if not a tap like Norm said.
::
::T.
:_____________________________________________________
:
:This radio does use a hum bucking coil, it also has a tapped field coil with one wire to the 80, one to the plate of the output tube and one for the B+. See Riders 8-10. Try Playthings of the Past for a transformer.
:
:Dave
Send me your email address and I will send you the schematic.
easyrider8 at aol.com
Dave
Norm
http://www.nostalgiaair.org/PagesByModel/537/M0012537.pdf
:Mike
:
:Send me your email address and I will send you the schematic.
:
:easyrider8 at aol.com
:
:Dave
You are correct Norm, I was looking at the wrong one.
Dave
::Just a 2 wire field in this schematic:
::
::Norm
::
::http://www.nostalgiaair.org/PagesByModel/537/M0012537.pdf
::
:______________________________________________________
:
:You are correct Norm, I was looking at the wrong one.
:
:Dave
A modern speaker won't look as nice, but will work quite well. Be sure to match the impedance properly for optimum power. Typically old radios used 3.2 ohm speakers (or 3.5). Try several impedances and see which one works the best (obtain several speakers of similar design and construction, but with different impedances).
T.
T.
You mentioned in a later post here that the field coil had a third wire. Measure between it and the other two field leads and see if there is resistance. Perhaps part of the field wind ing is good. May be enough resistance that the field could be powered to operate the speaker.
Radiodoc
:Finally got a 1936 Arvin model 518 working. The biggest hurdle for me was figuring out that the speaker field, which also serves as part of the power supply filter, doesn't work. I happened to have a 5 henry, 50 Ma filter choke in the drawer, so I wired it into the circuit. I did not unhook the speaker field wires. The radio came alive, though it's a little fuzzy. I have three questions:
:
:1. All that the service informations says about the speaker field is that it is 1,600 ohms. Would a different size filter choke work better than the one I installed?
:
:2. Should I unhook the wires to the speaker field?
:
:3. Why does the speaker work. I thought the speaker field created an electromagnet for the speaker, which was necessary for it to function.
:
:Thanks in advance for your thoughts.