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Second Newbie Project: Wiring a WE Candlestick Rotary (51/151 AL?) to a 634AT Subset

Started by oyang, September 02, 2015, 12:10:52 AM

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oyang

I opened the transmitter and found it is a 635A.  So this means that the 706A receiver with the HA1 unit is the correct part for this phone?  If so, I lucked out to have it already in my possession from a small group of random parts I got!
"In theory, theory and practice are the same. In practice, they aren't."

G-Man

An F1 transmitter capsule mounted in a 635A ("Bulldog") transmitter housing. The F1 transmitter and HA1 receiver are a good combination.

oyang

"In theory, theory and practice are the same. In practice, they aren't."

poplar1

Yes, it is a 151AL, because of the hookswitch configuration (4 leaves). It is true that many 151ALs have the 635A transmitter and 706A receiver, but those two parts can also be found on other models. However, the conversion of an older model to a 151AL was done only in the Western Electric repair shops, and not in the field by an installer-repairman.

The 151AL is an anti-sidetone model. It can be used with an anti-sidetone subset such as 634A, 634BA, 684A, 684BA, 495BP subset; or the base of a 302 telephone set. It can also be used with a sidetone subset --  534A, 584A, 295A, 334A -- in which case, the black conductor is taped and stored inside the subset.  For best results, use an anti-sidetone subset.

You will need to rewire the set. The receiver connects to W on the dial and GN on the left terminal block, rather than directly to the hookswitch.  You will need 5 conductors between the hookswitch (4) and transmitter (1) to the base of the phone, in addition to the short transmitter wire shown going from the transmitter to the hookswitch. Since you are using a 5H dial, rather than a 2A shown in the diagram, you will need to strap the BB and R terminals together on the dial.
"C'est pas une restauration, c'est une rénovation."--François Martin.

NorthernElectric

Quote from: oyang on September 08, 2015, 11:48:30 PMI have no idea what the issues and barriers are to "trying to connect a sidetone set to an anti-sidetone subset" because I have no idea what those terms mean.

The term sidetone refers to acoustic feedback from transmitter to receiver; in other words, how much you can hear yourself talk.  Circuitry was developed in the 1920s to limit this effect to a more optimum level and dubbed 'anti-sidetone'.  Since your phone is indeed a 151AL, you don't need to worry about connecting a sidetone phone to an anti-sidetone circuit.  Should you find yourself in that position in the future, there are a couple of topics on that subject (with wiring diagrams) on the forum which I myself have made use of.  I currently have a 20-AL connected to a 684-BX subset in use on my line.  But, no sense going into that now as it might confuse and distract you from the project at hand.
Cliff

G-Man

Quote from: NorthernElectric on September 09, 2015, 06:58:19 AM
Quote from: oyang on September 08, 2015, 11:48:30 PMI have no idea what the issues and barriers are to "trying to connect a sidetone set to an anti-sidetone subset" because I have no idea what those terms mean.

The term sidetone refers to acoustic feedback from transmitter to receiver; in other words, how much you can hear yourself talk.  Circuitry was developed in the 1920s to limit this effect to a more optimum level and dubbed 'anti-sidetone'.  Since your phone is indeed a 151AL, you don't need to worry about connecting a sidetone phone to an anti-sidetone circuit.  Should you find yourself in that position in the future, there are a couple of topics on that subject (with wiring diagrams) on the forum which I myself have made use of.  I currently have a 20-AL connected to a 684-BX subset in use on my line.  But, no sense going into that now as it might confuse and distract you from the project at hand.

I don't want to split hairs but in the interest of accuracy, acoustic feedback results in a "howling" or "squealing" sound, which was one of the banes of early handset development. This was the reason that Western Electric placed cotton balls in the receiver bowl of hollow G-series handset housings.

It is perhaps more familiar when a public address system has the gain turned up too loud, causing the microphone to pick up the sound emanating from the speakers. 


unbeldi

Quote from: NorthernElectric on September 09, 2015, 06:58:19 AM
Quote from: oyang on September 08, 2015, 11:48:30 PMI have no idea what the issues and barriers are to "trying to connect a sidetone set to an anti-sidetone subset" because I have no idea what those terms mean.

The term sidetone refers to acoustic feedback from transmitter to receiver; in other words, how much you can hear yourself talk.  Circuitry was developed in the 1920s to limit this effect to a more optimum level and dubbed 'anti-sidetone'.  Since your phone is indeed a 151AL, you don't need to worry about connecting a sidetone phone to an anti-sidetone circuit.  Should you find yourself in that position in the future, there are a couple of topics on that subject (with wiring diagrams) on the forum which I myself have made use of.  I currently have a 20-AL connected to a 684-BX subset in use on my line.  But, no sense going into that now as it might confuse and distract you from the project at hand.

An important correction to understand sidetone correctly:  It is NOT acoustic feedback, but electric feedback from the transmitter to the receiver through the induction coil of the telephone set.

Acoustic feedback also existed in the early handsets and was of great trouble that actually held up the use of the combined handsets by Western Electric for almost 20 years, until they figured out how to make a handset with a mechanical resonance frequency far removed from the peak response of the typical transmitter and receiver elements of the time.  The early handsets were extremely susceptible to self-resonance resulting in howling sounds.

Even after the introduction of the G1 handset with the 500-set in 1950, the handsets were still equipped with a cotton ball in the handle hollow by the receiver cavity to break acoustic resonances in the air in the handset.

Sidetone is mainly a nuisance, but partially important and wanted, but only to a small degree so that the speakers can hear themselves enough similar to a face-to-face conversation. With too much sidetone most people lower their voices to a level at which telephone transmission is too weak.  It also impairs understanding of the remote party by the amplification of room noise through the handset.

oyang

It makes sense now; thank you!  The explanations about electrical and acoustic feedback are really helpful in understanding WHY things are laid out as they are, which definitely helps me understand HOW they are laid out. Things I read before that didn't sink in now make sense from the explanations you have given me.  Without this context, info I was finding was just patterns to memorize or follow.

So it seems that I'm lucky and have all compatible parts that should work together with minimal jury-rigging, assuming nothing is broken. A 51AL would have been more problematic with this subset, so I'm fortunate that I got at 151AL since I didn't know the difference. As the old saying goes, even a blind squirrel finds a nut sometimes.
"In theory, theory and practice are the same. In practice, they aren't."

oyang

Regarding this subset (634A):

Is the wiring correct as I have it?   The dotted black line connections do not exist currently, but seem to be shown in the diagram showing the hookup of the 202 to the 634A.  What are those side contacts, and would I have to solder wires to make those dotted black line connections?

Thanks all,

Otto
"In theory, theory and practice are the same. In practice, they aren't."

G-Man

I'm not sure what an "SMF" is nor why you have a black wire routed to the ground terminal. According to the wiring diagram for the 151AL, there should be four-wires (not three) in the cord between your deskstand and subset.
unbeldi, popular1 and phonesrfun have already addressed the best wiring connections and practices, so you may wish to instead reread their comments and consult with the diagram that has already posted for this specific instrument (desk stand) instead of for a 202 desk set.

poplar1

The 634AT originally had a cold cathode tube, rather than a capacitor, in the ringer circuit. So in order to convert a 634AT back to a 634A, besides disconnecting the tube, a second capacitor is needed.

The diagrams for a 634A and other equivalent subsets show two capacitors, though they are often physically contained in one metal enclosure. The two capacitors are connected as follows:

Talk capacitor (2 Microfarads): Red to C on induction coil, Black to BK terminal (not GND).
Ringer capacitor (0.5-1.0:? Microfarad): Yellow to  L2-Y on induction coil,   Slate to K terminal
Ringer: Red to L1 on induction coil; Black to K.
"C'est pas une restauration, c'est une rénovation."--François Martin.

NorthernElectric

Quote from: G-Man on September 10, 2015, 05:06:18 AM
I'm not sure what an "SMF" is nor why you have a black wire routed to the ground terminal.

I believe that comes from oyang attempting to correlate the wiring diagram that he had for a 634BA to his incomplete 634AT.

So 'SMF' should be .5 MF and II47 is probably a date code that the artist of the wiring diagram included in his drawing, and oyang drew these on to the photo of his subset to represent connections to the 2nd capacitor which poplar1 has stated his subset is not equipped with.
Cliff

oyang

Quote from: NorthernElectric on September 10, 2015, 08:48:47 AM
Quote from: G-Man on September 10, 2015, 05:06:18 AM
I'm not sure what an "SMF" is nor why you have a black wire routed to the ground terminal.

I believe that comes from oyang attempting to correlate the wiring diagram that he had for a 634BA to his incomplete 634AT.

So 'SMF' should be .5 MF and II47 is probably a date code that the artist of the wiring diagram included in his drawing, and oyang drew these on to the photo of his subset to represent connections to the 2nd capacitor which poplar1 has stated his subset is not equipped with.

Yes that is right, thanks.  As I've mentioned, I'm a complete novice and have no background in these areas, so I'm sorry for making mistakes about things that are obvious to everyone.  One assumption I made (wrong) was that the internal wiring of the 634 subset would be the same configuration regardless of the phone being added to it, and another mistake was not realizing that the 634BA, 634AT, and 634A are all different in significant ways.

So I'm still (sorry) confused about the subset and its wiring.  This subset was a 634AT but it is now missing a cathode tube.  I found this thread here:

http://www.classicrotaryphones.com/forum/index.php?topic=4995.0

Will it work with the current parts, or with minimal (and reversible) modifications within the abilities of a biologist with a screwdriver?  Does it need a second capacitor to work, and if so where do I get one and how do I add it? Seems like this is a slightly rare-ish item and I wouldn't want to ruin any historical value. Alternatively, should I try to restore it to original function by adding a tube?  I do see there are wiring diagrams available for the original 634AT (although I'd need to ask you guys if these would work for the 151AT).

I found this:

http://vacuumtubesinc.com/index.php/vacuum-tubes/426a-we.html

There are other places selling them too; apparently they aren't hard to get. 

To summarize my questions:

1. Will this subset work for my 151AL with its current parts, and if so how do I wire it given the missing tube?
2. If the subset needs additional part(s) to work, can I make it work with simple modifications like adding another capacitor, and if so what and how?
3. Is it instead worth restoring to original specifications by adding a tube?

What do you guys think?

Otto

P.S. If I add a "flux capacitor," can I make calls back in time?  Ha!
"In theory, theory and practice are the same. In practice, they aren't."

unbeldi

Otto,  While it is surely a nice and worthwhile effort to restore a 634AT to its original configuration, you have to realize that those were not intended to be used on todays 2-wire telephone circuits.

The electron tube is like a diode switch, it was used with polarized pulsed ringing voltage using a ground connection as the return path to the central office.  It was only used for fully selective ringing on party-lines.  A tube was used on lines that were very sensitive to inductive noise resulting from electrical unbalance of the line because of the ground connection for the normal ringers that used a capacitor instead (in a 634A or BA).  An electron tube has an extremely high electrical impedance when not  in active use while ringing, while a capacitor has a much lower one.

While it is cute to see the tube glow, it has no practical value anymore, and would be best demonstrated if you also want to construct a traditional telephone line with two conductors plus ground.

So, the more practical activity would be to simply buy a ten cent capacitor.

What is a little odd, is that your set has a 0.5 µF capacitor installed already.  Are you reading the value correctly?  Normally a 634AT has a 2 µF capacitor installed for the audio circuit, and you would have to add the ringing capacitor with a value of 0.5 µF for a high-impedance ringer, or 1 µF for a low-impedance ringer.  It looks like yours has low impedance (2 x 700 Ω).

If your indeed have a 0.5 µF unit,  you already have the ringing cap and need the audio part.  0.5 µF is too small for the audio signals, you'd be loosing greatly in audio volume.


PS: looking at your diagrams, not sure anymore which are yours...   Does the condenser in your set have four terminals or only two?

What you really would like to have for a 1947 634A is a two-condenser can, like I am showing here:
The first one is a 194B (2 µF + 0.5 µF)  and the second is a 194A (2 µF + 1 µF), the correct one for a 1400 Ω ringer.