There is a great article by Bill Jeffrey in the "References" section of this site on Radiola 18 Electrical Restoration.
The following is from that article:
"This volume control is a big wirewound power rheostat, much larger than the function requires. It is unusual in that it has two resistance tracks. The main track totals about 3.3 kohms, and as in an ordinary rheostat, is in contact with the wiper over the full rotation of the control (about 3/4 of a turn). The pot is physically large in order to make room for a second resistance track which extends from the ground end to about 1/3 of the rotation. This second track, which totals only about 22 ohms, is mounted just inboard of the first, pressed against it, and in electrical contact with the main track all along its length. The overall effect is that, as the wiper comes up from the ground end, the resistance (and thus signal strength) increases quite slowly for the first third of the rotation, and then much more quickly thereafter. This gives a variable rate of control - slow at the low volume (high signal strength) end, and a faster adjustment at the top end. This is an approximation to the later "audio taper" pots."
Gary
:Does anyone know what the resistance of the volume control is? Thanks
:Greg
:Hi Greg,
:
:There is a great article by Bill Jeffrey in the "References" section of this site on Radiola 18 Electrical Restoration.
:
:The following is from that article:
:
:"This volume control is a big wirewound power rheostat, much larger than the function requires. It is unusual in that it has two resistance tracks. The main track totals about 3.3 kohms, and as in an ordinary rheostat, is in contact with the wiper over the full rotation of the control (about 3/4 of a turn). The pot is physically large in order to make room for a second resistance track which extends from the ground end to about 1/3 of the rotation. This second track, which totals only about 22 ohms, is mounted just inboard of the first, pressed against it, and in electrical contact with the main track all along its length. The overall effect is that, as the wiper comes up from the ground end, the resistance (and thus signal strength) increases quite slowly for the first third of the rotation, and then much more quickly thereafter. This gives a variable rate of control - slow at the low volume (high signal strength) end, and a faster adjustment at the top end. This is an approximation to the later "audio taper" pots."
:
:Gary
:
:
:
::Does anyone know what the resistance of the volume control is? Thanks
::Greg
I have never re-wound one of these and I dont't expect that to be a very simple task. I have a Radiola 18 but have not yet restored it. I am saving it until I can dedicate a lot of time to it.
If the wire is copper it is fairly simple to determine the gauge using standard wire tables. For a 3.3K resisitance, the wire must have 3.54 ohms / turn. What is the length of 1 turn? Once this is known the wire gauge can be determined.
Alternately, have you located the break in the wire? If it is near one end you may be able to repair it without having a big impact on the resistance.
Gary
:Thanks Gary, Have you ever rewound one of these? What would be the proper wire to use? I would like to give it a try but am not sure of the type of wire. I do know that mine had 933 turns.
:Greg
:
::Hi Greg,
::
::There is a great article by Bill Jeffrey in the "References" section of this site on Radiola 18 Electrical Restoration.
::
::The following is from that article:
::
::"This volume control is a big wirewound power rheostat, much larger than the function requires. It is unusual in that it has two resistance tracks. The main track totals about 3.3 kohms, and as in an ordinary rheostat, is in contact with the wiper over the full rotation of the control (about 3/4 of a turn). The pot is physically large in order to make room for a second resistance track which extends from the ground end to about 1/3 of the rotation. This second track, which totals only about 22 ohms, is mounted just inboard of the first, pressed against it, and in electrical contact with the main track all along its length. The overall effect is that, as the wiper comes up from the ground end, the resistance (and thus signal strength) increases quite slowly for the first third of the rotation, and then much more quickly thereafter. This gives a variable rate of control - slow at the low volume (high signal strength) end, and a faster adjustment at the top end. This is an approximation to the later "audio taper" pots."
::
::Gary
::
::
::
:::Does anyone know what the resistance of the volume control is? Thanks
:::Greg
I have the Radiola 18 service manual. The volume pot is listed as 2500 ohms, wire wound. This is an antenna attenuator-type volume control, which carries no current.
Wire-wound pots are usually made of special resistance wire which is impossible to solder. You could replace the pot with a modern, audio-taper pot. RadioDaze sells a 5K audio pot that ought to work fine (part no. R-SPA-5K). Since the pot is under the chassis, a modern replacement shouldn't bother anybody too much.
:Greg,
:
:I have the Radiola 18 service manual. The volume pot is listed as 2500 ohms, wire wound. This is an antenna attenuator-type volume control, which carries no current.
:
:Wire-wound pots are usually made of special resistance wire which is impossible to solder. You could replace the pot with a modern, audio-taper pot. RadioDaze sells a 5K audio pot that ought to work fine (part no. R-SPA-5K). Since the pot is under the chassis, a modern replacement shouldn't bother anybody too much.
Is the service manual for the Radiola 18 available in PDF?
Gary
:Greg,
:
:I have the Radiola 18 service manual. The volume pot is listed as 2500 ohms, wire wound. This is an antenna attenuator-type volume control, which carries no current.
:
:Wire-wound pots are usually made of special resistance wire which is impossible to solder. You could replace the pot with a modern, audio-taper pot. RadioDaze sells a 5K audio pot that ought to work fine (part no. R-SPA-5K). Since the pot is under the chassis, a modern replacement shouldn't bother anybody too much.
:Greg,
:
:I have never re-wound one of these and I dont't expect that to be a very simple task. I have a Radiola 18 but have not yet restored it. I am saving it until I can dedicate a lot of time to it.
:
:If the wire is copper it is fairly simple to determine the gauge using standard wire tables. For a 3.3K resisitance, the wire must have 3.54 ohms / turn. What is the length of 1 turn? Once this is known the wire gauge can be determined.
:
:Alternately, have you located the break in the wire? If it is near one end you may be able to repair it without having a big impact on the resistance.
:
:Gary
:
::Thanks Gary, Have you ever rewound one of these? What would be the proper wire to use? I would like to give it a try but am not sure of the type of wire. I do know that mine had 933 turns.
::Greg
::
:::Hi Greg,
:::
:::There is a great article by Bill Jeffrey in the "References" section of this site on Radiola 18 Electrical Restoration.
:::
:::The following is from that article:
:::
:::"This volume control is a big wirewound power rheostat, much larger than the function requires. It is unusual in that it has two resistance tracks. The main track totals about 3.3 kohms, and as in an ordinary rheostat, is in contact with the wiper over the full rotation of the control (about 3/4 of a turn). The pot is physically large in order to make room for a second resistance track which extends from the ground end to about 1/3 of the rotation. This second track, which totals only about 22 ohms, is mounted just inboard of the first, pressed against it, and in electrical contact with the main track all along its length. The overall effect is that, as the wiper comes up from the ground end, the resistance (and thus signal strength) increases quite slowly for the first third of the rotation, and then much more quickly thereafter. This gives a variable rate of control - slow at the low volume (high signal strength) end, and a faster adjustment at the top end. This is an approximation to the later "audio taper" pots."
:::
:::Gary
:::
:::
:::
::::Does anyone know what the resistance of the volume control is? Thanks
::::Greg
This pot acts as a voltage divider between the antenna and the ground connection. See if connecting, or not connecting, an external ground makes a difference in the minimum volume. My thinking is that with an external ground connection, the RF might sneak right up the ground wire. Make sure that one end of the pot is connected to chassis ground.
This 7-tube TRF has three RF stages, a detector, and two AF stages - which gives plenty of gain. Sometimes the RF can jump right past the antenna/volume control and directly into the set.
To reduce the overall gain a little, you could try cutting back the 1.5-V filament voltage with a power resistor in series with the 1.5-V supply to the '26 tubes.
:Greg: I don't know why a 5K pot wouldn't attenuate the antenna signal any more or less than the original 2.5K pot.
:
:This pot acts as a voltage divider between the antenna and the ground connection. See if connecting, or not connecting, an external ground makes a difference in the minimum volume. My thinking is that with an external ground connection, the RF might sneak right up the ground wire. Make sure that one end of the pot is connected to chassis ground.
:
:This 7-tube TRF has three RF stages, a detector, and two AF stages - which gives plenty of gain. Sometimes the RF can jump right past the antenna/volume control and directly into the set.
:
:To reduce the overall gain a little, you could try cutting back the 1.5-V filament voltage with a power resistor in series with the 1.5-V supply to the '26 tubes.
gary, I was suprised to hear the radiola 18 described as "Sensitive", but perhaps you are experiencing regeneration in the ist RF amplifier. I had that problem when replacing an original VC with a modern pot. The simple thing to do would be to put a "losser" resistor in the grid circuit od the first RF amplifier and see whether the volume control improves. you hshold not experience the nand capacity effect on a set that is operating properly. try a 20, 50, and 100 ohm resistor in the grid circuit of the tube and see what happens.
::Hi Gary, each turn is 1 1/16", I dont know what gauge the wire is but it is very small, I have a spool of 30 gauge and it looks to be half that size. It had a lot of breaks in it, lost track after a dozen or so. I was looking at some resitance tables and I dont think magnet wire will work, it will have to be nichrome resistance wire that is enamel coated, I have yet to find any of this. Other than the volume control the radio works good, a little to good. I installed a 5k pot and with no antenna attached the lowest volume is a little to loud.
::Greg
::Greg
::
::
:::Greg,
:::
:::I have never re-wound one of these and I dont't expect that to be a very simple task. I have a Radiola 18 but have not yet restored it. I am saving it until I can dedicate a lot of time to it.
:::
:::If the wire is copper it is fairly simple to determine the gauge using standard wire tables. For a 3.3K resisitance, the wire must have 3.54 ohms / turn. What is the length of 1 turn? Once this is known the wire gauge can be determined.
:::
:::Alternately, have you located the break in the wire? If it is near one end you may be able to repair it without having a big impact on the resistance.
:::
:::Gary
:::
::::Thanks Gary, Have you ever rewound one of these? What would be the proper wire to use? I would like to give it a try but am not sure of the type of wire. I do know that mine had 933 turns.
::::Greg
::::
:::::Hi Greg,
:::::
:::::There is a great article by Bill Jeffrey in the "References" section of this site on Radiola 18 Electrical Restoration.
:::::
:::::The following is from that article:
:::::
:::::"This volume control is a big wirewound power rheostat, much larger than the function requires. It is unusual in that it has two resistance tracks. The main track totals about 3.3 kohms, and as in an ordinary rheostat, is in contact with the wiper over the full rotation of the control (about 3/4 of a turn). The pot is physically large in order to make room for a second resistance track which extends from the ground end to about 1/3 of the rotation. This second track, which totals only about 22 ohms, is mounted just inboard of the first, pressed against it, and in electrical contact with the main track all along its length. The overall effect is that, as the wiper comes up from the ground end, the resistance (and thus signal strength) increases quite slowly for the first third of the rotation, and then much more quickly thereafter. This gives a variable rate of control - slow at the low volume (high signal strength) end, and a faster adjustment at the top end. This is an approximation to the later "audio taper" pots."
:::::
:::::Gary
:::::
:::::
:::::
::::::Does anyone know what the resistance of the volume control is? Thanks
::::::Greg