800B Broken Commutator Finger

[Joseph W Strickland]

This morning I began a closer look at the rear commutator assembly. I had noticed a piece of paper down in the bottom of the outer cover. I removed all the screws holding the chrome plate in place and then removed the C-clip on the end of the shaft from the flex-coupler mounted on the rear end of the tuning capacitor shaft. I managed to remove the piece of paper. It turned out to not be anything significant as far as I can tell. It looks like a piece of light beige masking tape that fell down in there. I began to clean the bottom inside edge of the chrome plated back cover. A small piece of metal fell out. This turned out to be one of the spring contacts from the most counter-clockwise station preset within the small arc of 6 station presets ( viewed from the back and connected to a solid orange wire). This spring contact broke off right at the edge of the stack of insulation material where the orange wire connected. I hated to see this. It means that I will have to find a way to repair this station preset contact assembly.

I am thinking that I may find a piece of spring contact material from a used relay that I can use to make the repair. If not, I could remove one of the preset contact assemblies from the parts unit that I have, although I would prefer not to have to do that. There is the potential to restore that unit also (although it is now missing its drive motor). I believe the original material used to make this spring contact was heat tempered beryllium copper with a silver plating.

I looked at the commutator disc surface and see that some of its nickel plating is worn through down to the base steel metal. This might be a problem down the road. I won't know until I get to the point of checking out the electric preset tuning function. It is possible that if the disc surface is cleaned as much as possible and given a light coating of Penetrox A or E that it may correct for a poor contact there. I also have some silver impregnated grease that is normally used for CPU mounting in computers. It not only provides a very efficient heat conductor but also makes a very good low resistance connection. The key there is to only use a very thin coating. It would not be good to use so much that it would lead to excessive build-up on the contact fingers.

The problems we encounter in restoring these older radios challenges our ingenuity. If any of you have dealt with problems in the electric tuning commutator area I would appreciate hearing your solutions.

Joe

[Norman S Braithwaite]

Joe:

I can send you a couple of the preset spring assemblies for $5.00 to cover shipping.  They can be disassembled by removing a needle size pin from a groove in what appears to be a nut on the inside of the shroud.

Norman

[Joseph W Strickland]

Norman;

That would be great! Do you have PayPal? I do and could send payment that way, otherwise I could send you a check by USPS.

Joe

[Norman S Braithwaite]

Joe:

Thanks.  I have sent you an e-mail.

Norman

[Joseph W Strickland]

I learned something after discovering the broken contact finger in the rear tuning preset assembly. At first I could not understand why this happened. Now after having the area disassembled and looking at this early model versus the late model I have, I realize that the reason the finger got broken off is that someone who worked on it previously messed with this area and put it back together with the wires going to the tall brackets of the outer arc behind the commutator disc. Those wires are supposed to be in front of the commutator disc so that they stay away from the wires to the short brackets for the contacts in the small arc. As a result the wires from the tall brackets got tangled on the contact fingers from the short brackets and broke one of the fingers off. The two groups of wires have to be kept apart and the commutator disc is the thing that separates item. Keeping the wire bundles separated is also the reason why there are tall and short contact brackets employed.

Owners/restorers must keep the wire dress and parts stack-up in the preset tuning contacts area exactly like it was originally done at the factory. One way to keep oneself straight about this design area is to take a series of pictures of the original wire dress and parts placement/sequence on the tuning shaft etc. as you begin to dis-assemble it for service. Care needs to be exercised while working on the preset tuning area to keep from getting wires and tools snagged on the contact fingers.

Joe

[Joseph W Strickland]

Here are some pictures of the inside of the backplate and the commutator disc for the pushbutton tuning system. You can see the date imprint on one picture highlighted. Note the accumulation of dirt and corrosion even after some light cleaning. Another picture shows this area after a thorough cleaning and polishing.

Here is a picture of the commutator disc. It has been cleaned and polished, but as you can see the area where the contact fingers touch has worn through completely to the base metal underneath. I have doubts that this will ever work well. In looking at the disc, it appears that the wires could be swapped and the bottom part of the disc could be rotated 180 degrees into service with the contact fingers. You can also see where previous efforts at cleaning this disc resulted in lots of fine scratches on the surface. This type of cleaning is not a good practice as it tends to open up the surface to easier penetration of the precious metals to the base metals underneath. The disc is made from steel plated first with copper and then with nickel from its appearance.

Joe

[Joseph W Strickland]

The existing commutator disc of my early 800B is so pitted and corroded that it will never clean up well enough to suit my preferences and look nice as well as work well so......

I did some research this morning dealing with the suitability of several types of sheet metal to use for replacement of the halves of the commutator disc. I found that #304 stainless steel will accept at least some types of rosin solder and is resistant to corrosion. It conductivity is not as good as copper, brass and nickel, but the size of the disc is small enough that this should not be a problem. Consequently, I have ordered two 10 inch square pieces of #21 gauge (.036 inch thick) type 304 stainless steel alloy plates from McMaster-Carr.

I plan to disassemble one of the discs that I have by removing the rivets and screws. The center hole that was made for the shaft and bearing to pass through is 0.785 inches in diameter, so a 3/4 inch punch will likely work OK for that. I may have to take the sheet to a machinist to get it cut into an 8 inch diameter circle, then it needs to be cut straight across such that .050 inches of material is removed between the two halves of the circle. This should leave two pieces that are exactly the same size and the old plated pieces can be used as a template for drilling holes to accept new rivets or small nuts and screws for assembly to the bakelite strips that insulate the two halves of the commutator. It should not be difficult to create the small solder tabs which are about 1 3/4 inches from the center of the disc.

Using stainless steel will avoid the need for any separate plating expense and process. The back side could be polished until it approaches chrome plating in appearance. It is possible to buy the stainless steel plates already polished on one side.

I will let everyone know how this turns out.

Joe

[Norman S Braithwaite]

Joe, you are trying too hard.  There are ample 800B parts sets around from which to obtain decent replacement parts.  I don't have a spare at the moment but you should ask around before investing considerable time and money for reproduction of a reasonably available part.

Norman

[Joseph W Strickland]

Norman;

I guess I just hate to tear up a potentially restorable radio just to get a part out of it. However, then there is the issue - just how much work would have to be done on a given chassis to get it in decent working condition again. Sometimes I go to far in detail of restoration on some of my equipment. I think it is a disease! In any case, thanks for reminding me and pointing me in an easier direction.

In this instance I have already ordered some new stainless steel 10 inch plates from McMaster-Carr to use and a double blade circle cutter to use in my drill press for cutting the sheets into 8 inch disc. I am going to give it a try to see if I can be successful in doing it. I can use the hole cutting set-up even to cut speaker mounting holes too, so it will not become a dust catcher tool.

Joe

[Joseph W Strickland]

Here is a picture of the front side of the existing commutator disc. It looks pretty sad. Most of the upper half of the disc is very badly pitted all the way into the base metal.

Joe

[Joseph W Strickland]

Here is a drawing of the above Commutator Disc from the front side. It shows the details about the wire connection to the solder tabs there. One wire has a yellow dot of paint on it. The wire with the yellow dot is soldered after the first full turn around the shaft while the second wire continues another half turn and solders to the other tab. Each half of the disc is insulated from the other half and from the shaft that passes through it.

Joe

[Joseph W Strickland]

Here is a picture of the commutator disc viewed from the front of the radio tuner chassis that shows how the wires to the preset tuning contacts in the outer arc of the assembly are dressed in front of the commutator disc. This is the parts chassis that I bought recently. It is an unmolested unit, so the lead dress here is the original way it was done.

Joe

[Joseph W Strickland]

Here are some pictures of the commutator disc from the parts chassis I bought after cleaning and polishing. While this one is not perfect, I plan to use in in the early 800B I am restoring. It is in far better shape than the OEM commutator from the set. Both the front and back sides of the parts commutator look pretty decent, certainly not any worse than the rest of the chassis. I will keep the OEM commutator for rebuild as I mentioned earlier. I do not want to keep delaying work on the rest of the radio tuner chassis. So this commutator will replace the original one.

As you can see, there is none of the severe wear and scoring of the rear of this commutator disc.

Joe