Transmitter Cup - Capacitor??

[Dennis Markham]

This was a first for me.  I have been working on a Western Electric model 500 from 1973.  The transmitter cup has what I think is a capacitor connected between the terminals.  Can anyone tell me what the story is with that?  It's got a normal G3 handset and everything else is common for a phone of this year.  I've just never seen one before........

[Phonesrfun]

That's a capacitor, all right.  It may have been put there to alieveate some interferance from a local radio station.  Normally the circuit inside the network will do that just fine.  I have never seen one either if that is of any help.  That is a .01Mf.  The E1 handsets and early F1 handsets had a .005 (half the value of the one you have) as part of the handset.  These were to also guard against the carbon granules fusing themselves together over time.  However, as far as I know it is not necessary in the 500's.

Caps are frequently used to bypass radio station RF interferance, but it does no harm having it there.

-Bill

[LarryInMichigan]

As far as I am aware, all WE U1 receiver capsules have capacitors attached to their backs.

Larry

[Dan/Panther]

Larry;
Elaborate, where were the U1 utilized ?
D/P

[Dennis Markham]

Thank you Bill for that information.  I wondered if I should leave it or remove it.  You have answered that question.

[LarryInMichigan]

D/P,

U1s are the receivers inside G1n and G3 handsets.

[JorgeAmely]

Larry:

Those are more like diodes. They limit the voltage fed to the receiver to prevent discomfort to the user's ears.

[Dan/Panther]

Larry;
I'm confused, You wrote a that all U1 receivers have a capacitor.
I have looked at several of my G3 handsets, and can't find a single one Pre 1960 that has a capacitor, It must be an addition after 1960 or thereabouts. they have solder terminals, but no capacitor, and they haven't been removed.
D/P

[Dennis Markham]

I have seen some U1's that were modified with the diode and remarked U3.  Later elements were marked U3 apparently during the manufacturing process in later years.

[Phonesrfun]

Larry:

The thing on the back of the U1 is a varistor, which limits loud clicks.  The early ones had a 44A varistor in a round metal enclosure like the one shown in the phto.  Later ones had ones that are plastic coated and look like a colored tic-tac with leads coming out of each end.  

Internally, they are basically two parallel back-to-back diodes that will not limit normal voice level sounds in the receiver, but when a big voltage spike of about 2 or three volts comes along, they clamp it to keep the clicks from being too loud in the receiver.

-Bill

[Dan/Panther]

After looking even further into my handsets, I'm finding that the Diode or resistor on a transmitter marked U1  is rare before late 60's. Even later than that I can't find one on my sets before 1972.

Also I've just read on the website, "Variations of WE500 series sets" (link below) that handsets marked with 'Bell System property not for sale", is designated G15A, and replaces the G3 for modular use. I have several Handsets marked with "Bell System Not for sale", that are still hardwired.
D/P

http://www.paul-f.com/we500typ.htm#Handsets

[bingster]

It should still be there on the older ones, under the silver cap marked "44A."

[Phonesrfun]

I hope I don't come off as being too anal.  The attached photo should clarify.

The U1 and the U3 receivers are pretty much identical.  In fact, the one in the photo dated 4/11/56 has U3 stamped over the U1 that was originally embossed in the plastic case, so I suspect it was once refurbished.

The 44A varistor on the 2-2-51 U1 is the same thing as its more modern green one on the U3.  I suspect that the only difference between a U1 and a U3 is the earlier versus later varistor.

The vasristor is not a resistor.  It is a semiconductor known as a variabale resistor or "Varistor" for short.  Its resistance varies with the voltage applied to it.  

-Bill Geurts

[Dan/Panther]

O.K. Now I get it.
I didn't realize the 44A was the varistor.
Bill;
Are you kidding, I'm the one that feels Anal here. I always seem to make comments about things that aren't clear to me. Maybe someday I will know all of this stuff.
D/P

[Phonesrfun]

Bill;
Are you kidding, I'm the one that feels Anal here. I always seem to make comments about things that aren't clear to me. Maybe someday I will know all of this stuff.
D/P

The neat thing about having a forum is to be able to ask questions.  This forum, in particular, is great for that.  A couple of the other forums that are more closely associated with the two phone clubs can be intimidating.  I have experienced that first hand.  The other neat thing about this forum is that we have the ability to post pictures imbedded right in the post.  To me, this makes it particularly valuable.  A picture is worth a thousand words, as they say.

-Bill