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What is this?

Started by persido, October 11, 2014, 04:01:34 PM

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persido

I have opened a number of 302's, I have never come across this.
The phone is dated 8/41 thru out the set, I hope someone can give me some info.

Thanks...Scot

TelePlay

#1
A 61A filter. This number and a date should be on the back side.

http://www.classicrotaryphones.com/forum/index.php?topic=6192.msg73260#msg73260

unbeldi

#2
Quote from: persido on October 11, 2014, 04:01:34 PM
I have opened a number of 302's, I have never come across this.
The phone is dated 8/41 thru out the set, I hope someone can give me some info.

Thanks...Scot

It is a No. 61P filter to suppress radio interference by the dial. The interruptions of the loop current by the dial produce radio frequency signals that are picked up by radio sets.  The filter is a combination of inductance, resistance and capacitance according to this diagram.

The basic filter without mounting bracket is a 61A.  With the bracket for the 302 telephone it is a 61P.  In a 202 it is a 61N, and in a hangup type phone (G mount) it is a 61M.

persido

Great info, thanks a million Teleplay and Unbeldi.

Scot

compubit

I just found one in a 354 - the bracket says "61E", so I guess that's the designation for one in the 354 series...

Jim
A phone phanatic since I was less than 2 (thanks to Fisher Price); collector since a teenager; now able to afford to play!
Favorite Phone: Western Electric Trimline - it just feels right holding it up to my face!

unbeldi

Quote from: compubit on February 18, 2015, 09:03:39 PM
I just found one in a 354 - the bracket says "61E", so I guess that's the designation for one in the 354 series...

Jim

Yes, the suffix letter designates the particular mounting bracket that the filter is attached to.  The filter by itself without bracket is a 61A.

HarrySmith

Don't those also come in an "F" handset?
Harry Smith
ATCA 4434
TCI

"There is no try,
there is only
do or do not"

unbeldi

Quote from: HarrySmith on February 18, 2015, 09:37:50 PM
Don't those also come in an "F" handset?

The units that are mounted in handsets are just capacitors. They are connected across the transmitter, and act as a high-pass filter to short-circuit radio frequency to prevent it from getting into the carbon transmitter.  Such radio frequency could come from many sources, perhaps from fluorescent lights, electrical equipment, and close-by radio stations.

The No.61 filter was mounted across the dial pulse contacts to prevent radio frequency generation by the interruptions of loop current during dialing, which could be received by radios close by.  This filter is a low-pass filter to let pass the voice frequencies, but block anything above.

Babybearjs

do these still need to be installed? I pulled all mine out. I still have them, but don't use them unless necessary.
John

G-Man

Quote from: HarrySmith on February 18, 2015, 09:37:50 PM
Don't those also come in an "F" handset?

Harry

The following explains the reason why Bell installed condensers across the transmitter....

 

Cohering-

In common with a number of other materials, granular carbon is susceptible
to cohering. When cohering occurs the resistance and sensitivity of the
carbon are lowered and remain so until the transmitter is subjected to
mechanical agitation. Experience has shown that cohering will greatly reduce
the output of the handset transmitter and that fairly loud talking or a
sharp mechanical shock is required to restore it to its initial sensitivity.
Not infrequently cohering results from breaking the circuit connecting the
transmitter to the battery, as for example, when the subscriber depresses
the switch in the mounting in order to attract the attention of the
operator. A study of the electrical conditions responsible for cohering
under these circumstances has shown that the distributed capacity and the
inductance of the component parts of the station set are such that transient
oscillations of a frequency of several thousand kilocycles per second are
set up by the breaking of the circuit. Further investigation has shown that
the transmitter can be protected from the cohering effect of these
oscillations, without introducing a transmission loss at voice frequencies,
by connecting a condenser of a few thousandths of a microfarad capacity
across the transmitter to by-pass these transient currents.

In the case of the deskstand transmitter, these cohering effects have not
been important for several reasons. Probably the principal one is that the
mechanical impact incident to switchhook operation is carried directly to
the transmitter and prevents appreciable cohering.

-Carbon Preparation-

Substantial improvements in the technique of granular carbon manufacture
have been made in conjunction with the development of the new transmitter.
Roasting processes have been adopted which subject each granule to
substantially the same heat treatment and produce carbon of unusually
uniform electrical properties. Uniformity is further insured by the use of a
magnetic separator to remove granules having undesirably high iron content,
and the removal in an air stream of flat, wedge-shaped particles which tend
to cause carbon leakage in the transmitter by working their way between the
layers of paper which form the closure between the carbon chamber and
diaphragm.
Measures of this kind have been of particular value, not only in bettering
the transmission characteristics of the individual transmitter, but in
securing a uniform commercial product. Without these improvements, indeed,
it is doubtful if the production of the transmitter could be maintained at
the high rate now required without a sacrifice in the average quality of the
product.

poplar1

Quote from: G-Man on February 19, 2015, 08:20:04 AM


-Carbon Preparation-

Substantial improvements in the technique of granular carbon manufacture
have been made in conjunction with the development of the new transmitter.



Which "new transmitter" is being discussed? When copying information, it would be helpful to include the source.
"C'est pas une restauration, c'est une rénovation."--François Martin.

unbeldi

#11
Quote from: Babybearjs on February 19, 2015, 06:29:23 AM
do these still need to be installed? I pulled all mine out. I still have them, but don't use them unless necessary.
Well, these rotary dials work the same today as they did fifty years ago, and so does electricity.  The only thing that has changed is that there aren't many people listening to AM radios anymore. FM is much more immune to the noise.  The 500-series telephones had the filter permanently built into the network container.

The #129 transmitter capacitors were obligatory in the WECo transmitters in 1920s and 30s. They even kept them when converting 395 transmitters to 625 with the F1 element, but they were gone on the F1 handset on the 300-type telephone sets.  But for some reason most F1W handsets sold outside the Bell System still included them. The carbon granules in early transmitters were very susceptible to cohering, which is much enhanced by high-frequencies, while the carbon processing later apparently made this less of a problem.

Personally, I feel when they are present, I leave them, as this was part of the history of the telephone. It's an artifact that is worthwhile talking about, as it relates the telephone to the technology surrounding it.
Rarely does a filter become defective.

19and41

The things I learn on this site!  I had never heard of such a problem in over 40 years of working with communications equipment.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

unbeldi

Quote from: 19and41 on February 19, 2015, 02:07:25 PM
The things I learn on this site!  I had never heard of such a problem in over 40 years of working with communications equipment.
Really?   I think, key systems in particular, exhibited noise problems frequently, because of the extensive inside wiring required, which provides opportunity to pick up RFI, but also to radiate it when produced in the system.  Even small electrical problems, like cold solder joints, that were still marginally operational for the currents they carried, could demodulate radio transmitter signals for example,  producing a 'nice' background of the local radio station in your receiver.

G-Man

Quote from: poplar1 on February 19, 2015, 08:39:01 AM
Quote from: G-Man on February 19, 2015, 08:20:04 AM


-Carbon Preparation-

Substantial improvements in the technique of granular carbon manufacture
have been made in conjunction with the development of the new transmitter.



Which "new transmitter" is being discussed? When copying information, it would be helpful to include the source.

Hi popular1,

You may have missed the included quote; however, as was indicated by Harry's query, it was about the type-"F" handset and by extension, the F1 transmitter. If there is further interest, a search of the TCI SingingWires Listserve and the TCI Library will yield a wealth of information regarding the development of the "E" and "F" handsets and combined handset telephones such as the 302 and 500-sets.

Thanks.