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NE NU Handset: 129 Condenser in Transmitter Cavity

Started by KaiserFrazer67, April 07, 2019, 05:37:01 PM

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Hi all,

Just recently picked up this walnut Northern Electric NU handset from eBay, complete with HA1 receiver and F1 transmitter.  I'd recently purchased a very nice walnut NE Type 1 Uniphone with an F1 handset and BPO dial (which I will feature in a separate thread in the future); and while the walnut F1 looks nice enough on it, I do like the unique, distinctive look of the NU style.  During disassembly, I found a component in the transmitter cavity with which I am not familiar, having not seen it before in comparable WE F1 units.

First photo shows the shell of the NU handset after cleaning (sorry, the flash doesn't seem to bring out the walnut mottling).

Second photo shows the transmitter cavity after the transmitter was removed, with the component as installed upon discovery.

Third photo shows the component in question.  Stamping reads: "129D  III 39 / PATENTED / 1930".

Asking:  What is this thing and what does it do, and does it need to be there?  I first thought that it may be a device to dampen hookswitch 'pop', but I'd think such a device would either be located in the receiver cavity, or in the body of the phone itself.  Besides, the phone as I received it doesn't seem to have too much of a problem with hookswitch or rotary-dial 'pop' to begin with.

I do remember advice given in another post from DavePEI to canuckphoneguy that one shouldn't use a WE 302 as a basis for the wiring on an NE Uniphone--advice which I heed. [EDIT: That post is here: ] Unfortunately in my search on this forum and other Internet antique phone sources, I couldn't turn up any references to this component.  Again, I've never seen it included in an F1 set on a 302, but I'm aware that means very little concerning NE Uniphones.  The NU handset does look very similar, if not outright identical, to the F1 as far as wiring concept is concerned, so again I am unsure as to what this thing is supposed to do.

Thanks in advance for your help and expertise.

-Tom from Oakfield, Wisconsin-
-Tom from Oakfield, Wisconsin --  My CO CLLI & switch: OKFDWIXADS0--GTD-5 EAX

"Problems are merely opportunities in workclothes." -Henry J. Kaiser


I've just beem PMed with a link to the answer:

Jack Ryan's reply to that post: "It is a capacitor that is connected across the transmitter to prevent packing or incoherence in the presence of radio frequency
(RF) signals. The RF may be the result of close proximity to a radio transmitter or sometimes due to sparks or arcing of contacts.

"It is not designed to reduce clicking although its use may have that side effect.


Will leave this up here in case anyone else has the same question.
-Tom from Oakfield, Wisconsin --  My CO CLLI & switch: OKFDWIXADS0--GTD-5 EAX

"Problems are merely opportunities in workclothes." -Henry J. Kaiser


Western Electric F1W handsets (non-Bell markings) and all E1B and E1E handsets contain a 129-type condenser.

The 129-type condenser was required for common battery sidetone stations, even where was no radio frequency interference:


1.12 F1-type Handsets and some E-type hand sets are not equipped with an anti-packing condenser bridged across the transmitter as this is not required at anti-sidetone stations except in the case of radio interference from adjacent broadcasting stations. In this case a 129F condenser should be mounted under the transmitter contact springs of F type hand set or E type hand set equipped with a 625A
transmitter having 129F condenser. All F2 and F3 type handsets come equipped with this condenser.

1.13 Handsets if used at common battery side-tone stations must be equipped with a 129F condenser.
"C'est pas une restauration, c'est une rénovation."--François Martin.