I've a broken rheostat in a RADA radio. Wire is broken in 2 points.
Full unit replacement is almost impossible to find.
Put in a new modern rheostat easier, but not nice.
Is it too crazy to try to replace the resistive wire?
Where can i buy that wire?
Any other suggestion?
Thanks
Mauro

Not sure if Antique Electronics Supply (www.tubesandmore.com) sells Nichrome resistance wire anymore. They used to.

If you wish to tackle this tedious project, figure out how the phenolic that holds the old wire is fastened in place. Remove the clip from the front of the shaft and remove the slider assembly. If the phenolic is rivveted in place at the terminals, you will have to figure out how you are going to re-rivvet it in place, or perhaps use screws. Pop rivvets, if not used properly, break bakelite and phenolic. You are better off buying regular hollow brass rivvets at your hardware store and peening them over later. If you do not feel that you can repair the broken resistance wire, unwind it and figure out its resistance per foot by using your multimeter and measuring the resistance of a given segment of wire. This is the type of wire you will need to obtain from Antique Electronics Supply. Carefully wind the new wire around the phenolic. Try to keep your spacing even. Place the rivvets in the holes of the phenolic. Wrap the ends of the wire around these rivvets. Place the phenolic assembly back into the housing, slide rivvets through holes and peen them over. Reassemble control.

Sometimes you can find old looking controls at science surplus stores. I have one in town. If I had dimentions and resistance, perhaps I could locate one for you. Antique Electronics Supply sometimes carries old surplus controls. You can also try another trick--find a small modern control of the same resistance and wattage rating and gut your old control. If the shaft of the new control is correct and the control can be inserted in the old control, just put it inside the old control.

Thomas

:I've a broken rheostat in a RADA radio. Wire is broken in 2 points.
:Full unit replacement is almost impossible to find.
:Put in a new modern rheostat easier, but not nice.
:Is it too crazy to try to replace the resistive wire?
:Where can i buy that wire?
:Any other suggestion?
:Thanks
:Mauro

:I recently did a similar repair of a dual section graphite rheostat, including the graphite element itself. The hollow brass rivets of this size are called eyelets and are more readily found at a craft store in the bead area or hobby store, but swaging/peening them will be troublesome. The core (fish paper, phenolic) can be closely approximated with PAPER GASKET mat'l in varying thickness found in some auto parts stores. Carefully drill out the orig. rivets from the peened/swaged side (usually outside)and push them back thru the hole head first. My solution was to use small brass screws (4-40) with nuts vs rivets, space permitting. Place the screw upside-down in the chuck of a drill/drillpress and use a file to flatten the head to a size approximating the orig. rivet, insert in the same direction as the orig. You'll lose the screwdriver slot, but finger pressure will be sufficient to install small nut and lockwasher outside the case. There'll be a lug attached to the element,which passes thru a hole in the case or placed outside and riveted thru the element and case. Usually, a small thin washer is placed on the rivet before peening/swaging, but make sure there is enough rivet above the washer to allow the final step. If the lug is riveted directly onto the element, the swaging/peening can be fairly easy, whereas a screw/nut may interfere with re-assembly into the case. I found ww units of varying sizes in a local surplus stores, but unwinding and re-using the nichrome wire is next impossible. I have a few .jpg's of my process available by email.
marv
Not sure if Antique Electronics Supply (www.tubesandmore.com) sells Nichrome resistance wire anymore. They used to.
:
:If you wish to tackle this tedious project, figure out how the phenolic that holds the old wire is fastened in place. Remove the clip from the front of the shaft and remove the slider assembly. If the phenolic is rivveted in place at the terminals, you will have to figure out how you are going to re-rivvet it in place, or perhaps use screws. Pop rivvets, if not used properly, break bakelite and phenolic. You are better off buying regular hollow brass rivvets at your hardware store and peening them over later. If you do not feel that you can repair the broken resistance wire, unwind it and figure out its resistance per foot by using your multimeter and measuring the resistance of a given segment of wire. This is the type of wire you will need to obtain from Antique Electronics Supply. Carefully wind the new wire around the phenolic. Try to keep your spacing even. Place the rivvets in the holes of the phenolic. Wrap the ends of the wire around these rivvets. Place the phenolic assembly back into the housing, slide rivvets through holes and peen them over. Reassemble control.
:
:Sometimes you can find old looking controls at science surplus stores. I have one in town. If I had dimentions and resistance, perhaps I could locate one for you. Antique Electronics Supply sometimes carries old surplus controls. You can also try another trick--find a small modern control of the same resistance and wattage rating and gut your old control. If the shaft of the new control is correct and the control can be inserted in the old control, just put it inside the old control.
:
:Thomas
:
::I've a broken rheostat in a RADA radio. Wire is broken in 2 points.
::Full unit replacement is almost impossible to find.
::Put in a new modern rheostat easier, but not nice.
::Is it too crazy to try to replace the resistive wire?
::Where can i buy that wire?
::Any other suggestion?
::Thanks
::Mauro

Thomas, Marv,
Thanks for the advice.
First and major problem is to get the small quantity of wire needed to have the job done. Best would be to get it here in Italy. Meanwhile i've found an interesting website with some tables about size, power, resistance, alloy, etc, etc...
Fortunatly in the radio there is another reostat in good conditions. It does the same job as the other on a same tube. So same number of turns (about 140), same resistance (5 Ohm) and a good example to copy during the activity. Disassembly should not be too complex, only 1 rivet to manage. But it should be possible to keep it in place and pull the wire out from below it.
The main problem is to find the wire, just a few meters, not a full truck!
It will take time, but i'll do!
Mauro