Looking For Information About WE 300 Series Transmitter Diaphragm Insulators

[gands-antiques]

I've got several 300 series WE transmitters that do not have the little red mica insulator in he pocket on the top of the diaphragm and I'm trying to find out if the insulators can be purchased somewhere.

I'm also wondering if anyone has one of the insulators and can provide the diameter and thickness of the insulators are....I believe they are either 5/16" or 3/8" diameter and approximately 0.005" thick.

I'm also wondering if the insulators are even necessary for the transmitters to work.

Thanks,
Gary

[Jack Ryan]

I think a diagram or pictures would help as there are several "washer looking" mica parts.

Internal parts might be tricky to get but the basic parts required for mounting the element are available as a kit (reproduction)

For example: https://www.ebay.com/itm/133551340695

Jack

[gands-antiques]

Jack,
The mica insulators are the small round (5/16"-3/8" diameter) pieces that I believe are usually red the go in 300 series WE transmitters.

They go in the top pocket or indention in the aluminum plate / diaphragm to insulate the top bridge section of the transmitter from the aluminum plate. 

The only picture I have is one that John sent to me.  I'm attaching John's picture. It's the little red piece in the top right corner of the picture.

[gands-antiques]

The small mica insulator is where the leader is pointing to the forward most center location. Below the upper bridged assembly and the aluminum diaphragm plate. 

[Jack Ryan]

I am not very familiar with the internals of all the US WE transmitters but I understand them.

For some reason the images disappear in compose mode so I can't refer to the images.

The line drawing you posted is too low a resolution to make sense of. In any case, the part you refer to is not present on that transmitter. I have posted an image of a later transmitter (337) but it is very close to yours. The mica insulator is not named on the 337 as its function is taken over by the end of the moving carbon electrode.

In both the 323 (which is what I assume yours is) and the 337, the main diaphragm is under tension so in the case of the 323, the insulator must be present to maintain that tension.

The insulator does not need to be mica but it does need to be rigid so as not to damp the sound waves. It also can't rattle or move or those sounds will be picked up by the transmitter.

Just to be clear, not all WE 300 series solid back transmitters have the part to which you refer.

Jack

[gands-antiques]

I cut out a 5/16" circle and 3/8" circle and placed each in an original diaphragm pocket and I'm wondering if the  5/16" with partial coverage is okay or if full coverage with the 3/8" circle is better or required. 

[gands-antiques]

Jack,
The mica insulators are the small round (5/16"-3/8" diameter) pieces that I believe are usually red the go in 300 series WE transmitters.

They go in the top pocket or indention in the aluminum plate / diaphragm to insulate the top bridge section of the transmitter from the aluminum plate. 

The only picture I have is one that John sent to me.  I'm attaching John's picture. It's the little red piece in the top right corner of the picture.

[TelePlay]

The small mica insulator is where the leader is pointing to the forward most center location. Below the upper bridged assembly and the aluminum diaphragm plate.

The WE 329 shown in the above reply uses the older rubber washers on a diaphragm that is physically mounted to the carbon capsule by way of a threaded screw and nut. The 329 is the only 300 series transmitter to use the rubber washer. This, to the best of my research, is because the 329 is identical to the 229 except for in some way being electrically insulated, the improvement from the 229.

All WE 200 series, Kellogg, SC and AE transmitters used the fixed diaphragm and rubber washers to keep the diaphragm off of the faceplate.

All WE 300 series transmitters (except the 329) used a loose or floating diaphragm held between the face plate and carbon capsule using a baked, varnished muslin washer on the face plate and a small mica disk between the carbon capsule and the back of the diaphragm.

The 300 series diaphragm is unique in that it is not flat. It has a protruding edge or lip on the front side that is the only part of the diaphragm to contact the muslin washer (which is a hard and electrically insulating contact area). The ratio of the area of the contact lip with the rest of the diaphragm surface area is large meaning almost not of the sound vibrations created by the diaphragm are lost to contact with the face plate.

The 300 series diaphragm also has a small indented cup on the back side to hold the mica disk in place (another hard and electrically insulating contact area). That lets the diaphragm transmit sound wave vibrations into the carbon capsule with minimal attenuation from face plate contact and concentrated to the carbon capsule by way of the small small mica disk, the only part of the back side of the diaphragm making contact with the rounded point of the carbon capsule rounded metal "point."

The free floating diaphragm WE 300 series transmitter using the muslin washer and mica disk must have greatly improved the transfer of sound waves hitting the front of the floating diaphragm into the carbon capsule to both increased sound and clarity.

Without the mica disk between the carbon capsule rounded metal contact point and the diaphragm, it would be metal on metal contact which apparently WE determined was not the best way to make these transmitters.

The transmitters in the image below are from the 1923 WE Apparatus Catalog (from the TCI Library) lists some but not all transmitters using a baked muslin washer. It is always best to take the transmitter out of the cup to see if two spring fingers are holding a rubber washer in place (200 series plus the 329) or no spring fingers indicating a 300 series baked muslin washer between the lipped floating diaphragm and the face plate.

[gands-antiques]

Thanks a lot John. Great information

Would you happen to know if the picture I posted with 5/16" diameter with not quite full  coverage or 3/8" diameter full coverage is better?  I bought a special size 5/16" hole punch and if that size is good, I will go with it.   

I also found a commercial mica supplier that has o.oo5" thick sheet stock and they are  willing to help out with some material.

Thanks a lot...
Gary

[TelePlay]

Would you happen to know if the picture I posted with 5/16" diameter with not quite full  coverage or 3/8" diameter full coverage is better?  I bought a special size 5/16" hole punch and if that size is good, I will go with it.   

I also found a commercial mica supplier that has o.oo5" thick sheet stock and they are  willing to help out with some material.

I don't know. Try them and see.

I would think a slightly smaller disk would not affect the transfer of sound vibrations from the metal diaphragm to the carbon capsule post.

On the other hand, if a bit too large, that would cause the edges of the mica disk to be held away from the flat diaphragm, to get hung up on the sides of the indentation, leaving an air gap between the center of the diaphragm indentation and the mica disk, causing an incomplete physical connection between the metal diaphragm and the carbon capsule post. If too large, the carbon capsule post would not be in complete, direct physical contact with the diaphragm. There would be a gap between the mica disk and the metal diaphragm so only the vibrations from the edge of the mica disk in contact with the sides of the indentation (a small surface area and not at a direct angle) would cause sound vibrations to be lost to carbon capsule.

The idea set up would be for the carbon capsule post to be in direct contact with the center of the diaphragm indentation with only a thin piece of mica keeping the two metals from touching. And the mica is a hard material that would not by itself absorb vibrations, it would transmit all vibrations from the diaphragm to the carbon capsule post.

Try both and see which produces the strongest audio in the receiving telephone. I'd bet the 5/16" would work best. Let us know.


PS: If you wanted to try something else other than mica, today's materials would be a sheet of blister pack plastic from any store bought item that would be the same thickness. Won't be red but will be hard and electrically insulating. Blister pack comes in many thicknesses, just have to find one that is 0.005" or so thick. They didn't have plastic in the very early 1900's.

I just checked a couple of things I had in the workshop. WE 302 number card windows are 0.010" thick and the blister pack plastic containers that hold nuts and bolts and screws are 0.015" thick. Both are hard, stiff and might be a good substitute for mica even if they are a bit thicker. I would not use an easily flexible softer plastic, it does need to stay flat. Remember, the tension setting feature of the carbon capsule post on 300 series transmitters is adjustable and should accommodate a slightly thicker "mica" button. It might even have been designed to accommodate slight variances in mica button thickness back in the day.

[gands-antiques]

I finally got a hold of an original red Mica insulator and it measured 0.325" diameter and 0.005" thick.

I got a piece of 0.005" thick Mica from a Mica supplier and I bought a 5/16" (0.312" diameter) hand punch, so, my insulators are 0.013" smaller than the original ones. I haven't tried mine out yet but I think they will work just fine.

Gary

[TelePlay]

I finally got a hold of an original red Mica insulator and it measured 0.325" diameter and 0.005" thick.

I got a piece of 0.005" thick Mica from a Mica supplier and I bought a 5/16" (0.312" diameter) hand punch, so, my insulators are 0.013" smaller than the original ones.

In the realm of things, they are the same size.

It's better to be a bit smaller in diameter in that the smaller one will fit to the bottom of the diaphragm center indent/well creating direct contact between the vibrating diaphragm and the carbon capsule center post.

A larger one would hang up on the sides of the indent/well and attenuate the sound vibrations from getting from the floating diaphragm to the carbon capsule center post, which has a rounded end to minimize contact with the mica disk.

That was a very well designed WE transmitter. Thanks for posting the specs on the mica disk.