323 Type Transmitter Disassembly Question

[savageje]

I have a 323 Type transmitter from a 20AL desk stand that I am in the process of restoring. This is the first time I've done a candlestick phone restoration. Is there a way to remove the diaphragm from the transmitter cover plate?  I can't tell if it's threaded or friction fit and don't want to force it and risk damaging the diapraghm.

Also, the black coating on the diaphragm is peeling off. Assuming I can get the diapraghm out, should I remove the rest of this coating?  I wasn't sure whether this was factory applied or paint that someone had applied later.

[Ktownphoneco]

The transmitter assembly is composed of several parts and / or components.     Transmitter cup, transmitter faceplate, transmitter diaphragm.     The terms I use for the remaining parts, are transmitter bridge, and the transmitter brass button, which contains the carbon granules.
Since you haven't specified otherwise, I'm assuming the transmitter is a later version, without the slender threaded post fastened to the tip of the brass transmitter button, which inserts through the diaphragm.     The older version transmitter that I've just described, are usually found on the earlier 20-B desk stands.   

Remove the transmitter faceplate from the cup, disconnect the conductor leads.       Lay it face down on your work surface.     You will see 4 small round head machine screws holding the bridge to the back of the faceplate.     Remove those 4 machine screws, and carefully lift the bridge off and away from the diaphragm and set it aside.        That will expose the entire back surface of the diaphragm.     
Next, proceed with "CAUTION" here, see if the diaphragm with easily lift clear of the back of the faceplate.    There is a thin shellac coated insulator gasket, which is usually installed between the diaphragm, and the seat in which it sits on the back of the faceplate.       The "caution" part, is due to the fact that the shellac gasket can over time, become firmly attached to the back of the faceplate, and to a lesser extent, to the front rim of the diaphragm.    Therefore, you need to be careful in removing the diaphragm so as not to warp or damage it in the process.
I routinely encounter diaphragms with paint that's been damaged by age, or somebody having removed the mouth piece and stuck pencils, pens, whatever, into the mouth piece opening and poked around at the diaphragm and damaging the painted surface.

The older transmitters with the threaded post attached to the tip of the carbon button, and which passes through the diaphragm, has 2 very small thumb nuts positioned on either side of the diaphragm.       Therefore, once you remove the 4 machine screws holding the transmitter bridge and brass carbon button to the back of the faceplate, you will be lifting the bridge, button and diaphragm attached to it with the 2 thumb nuts in place.       This procedure needs to be done with extreme care because of the possible sticky insulating gasket situation described above.
If you would like a picture or two, with the parts labeled, let me know, and photograph a transmitter assembly for you.
I hope this helps.     

Jeff Lamb
 

[Ktownphoneco]

One correction to my previous post.     You did state it was a 323 transmitter, and I kind of forgot about that fact when I started explaining how to remove the diaphragm.   Assuming no one has tampered with the transmitter, and downgraded it using parts from an older version with the threaded transmitter pin and thumb nuts, the procedure I outlined initially is the proper one for that transmitter.    Disregard the information concerning the older transmitter.

Also, if you decide to go ahead and remove the diaphragm, then re-install it, do the following;      basically reverse the procedure to take the diaphragm out of, or off of, the transmitter faceplate.
"BUT" when you re-install the transmitter bridge and brass transmitter button, you will need to re-set the proper tension between the tip of the button and the diaphragm.     
You will notice a sort of triangular shaped nickel spring fastened with insulating materials, to the bridge assembly.     The tip of which, has a slot, which fits between the circular groove of the transmitter button tip.      That little device will set the proper tension between the transmitter button and the diaphragm, but you have to loosen the set screw that holds the rear brass shaft of the transmitter button to the transmitter bridge, before you re-install the bridge and button assembly over the diaphragm and onto the transmitter faceplate.        Once you have the bridge positioned correctly, and tightened down onto the faceplate, re-tighten that small set screw that clamps the rear shaft of the brass transmitter button.
The button and diaphragm will be properly tensioned at that point, and the transmitter should operate at it's full potential.

Jeff Lamb
 

[Phonesrfun]

The words of caution should be heeded. 

Some of us have destroyed a few of these learning how to "fix" them.  If you haven't got skills in dealing with delicate things, it might be best to leave it as is.  If you do go for it, here are another couple of pointers:  Jeff described some shellac covered gaskets/spacers.  I don't know specifically about a 323, but some of these spacers are also made of mica and if mica, the spacer between the diaphragm and the tip of the carbon button can be almost invisible, so don't let this drop on the floor.  You might not find it again before the vacuum does.

When you get it back together, the adjustment of the carbon button pressure against the diaphragm pretty much needs to be done while you have the transmitter connected in series with a battery and a receiver.  You have to find the "sweet spot" where it transmits the best while being held in its normal vertical position.  Know that these transmitters which are called "solid back" transmitters are highly sensitive to their position.  In other words, they won't work very well when held horizontally.  They are designed to be held as if they were in mounted on a desk stand (candlestick) phone.  As Jeff said, the adjustment is to loosen the set screw and adjust the pressure that the button exerts against the diaphragm, then tighten the screw when the best sound is achieved while listening.  I don't think there is any more scientific way of adjusting them than that.

Another caution: Don't try to open the carbon button.  You'll regret it. (words of experience)  However, if you suspect that there has been some clumping of the carbon granuals, it would be advisable to give the button a few raps on a table top to break up any clumping that has occurred over the years.  Candlesticks, in regular use are less susceptible to clumping because the transmitters are always being jarred around in the normal use of the phone.  However, if the phone has been sitting around for years, there may have been some clumping go on.

Also, they used rubber bushings in various places.  I am not sure about the 323 (my books are downstairs and I am lazy tonight)  However, if the 323 has rubber, typical places are around the tips of the diaphragm biasing springs and a bushing around the edge of the diaphragm itself.  These rubber parts often are hard and brittle and sometimes fall apart in your fingers while disassembling the transmitters.  These rubber parts can be a challenge to source some sort of acceptable substitute if they fall apart on you.



Best of luck

[Sargeguy]

Once you have disassembled the transmitter and are trying to remove the diaphragm from the faceplate, use a combination of heat and/or denatured alcohol to soften the shellac. 

For older style transmitters, gaskets can be made by cutting up old bicycle inner tubes.  Spring cushions can be made from vinyl heat shrink tubes used in electrical wiring, or vinyl dip solution.

[savageje]

Thanks, everyone for your responses.  I think that I am going to leave the diaphragm in the faceplate for now and put the rest of the transmitter assembly back together after I get everything repainted.  If I can get it adjusted to where it works well, I'm just going to leave it alone.  The only reason I would take it off is to refinish the surface of the diaphragm anyway -- and I don't think it's that important since it will be hidden behind the spit cup.  I would rather have a transmitter that works correctly.

[Phonesrfun]

Good choice.