ID candlestick -> AE Type 21

[Jack Ryan]

Subset has a two winding coil so it is Booster (SideTone) and Type 21 tekephone has 4 contact switch so it is SideTone as well....isn't it? I am not certain why they would reference Sidetone and Anti-Sidetone when both parts are Sidetone.

The notes on the circuit suggest AST operation but it is sidetone either way. The difference is booster or not.

The circuit shows a booster AE 21 but the hook switch configuration is identical to that of a 151AL. Therefore, using a WE circuit, the telephone can be AST. With luck, you could find an appropriate AE dial to go with it - or one of the Signal Corps dials that look like an AE dial.

Not perfectly correct but not obviously wrong.

Jack


Jack

[AE_Collector]

A regular AE 24A36 would be correct wouldn't it? With contacts as Stub drew in his extension to the drawing he posted. I have an Anti-Sidetone AE 32 subset that Gary would like to connect to his Type 21 stick but we want to ensure that this wont be too difficult to accomplish before I send it to him. I have a replacement bakelite base from a 1A set and a 24A36 dial for him as well.

Terry

[Jack Ryan]

I answered the wrong question. The usual AE dial with three spring shunt off normal contacts is correct for the AE circuit.
I suggested that the "sidetone AE 21" could be used in a Western Electric AST circuit as used in the 151AL. That circuit requires different dial off normal contacts - like a WE dial. It is possible to get an AE dial like that and the Signal Corp dials would do - as I said; if you are lucky. Otherwise the circuit would have to be modified.

With an old 3C transmitter and the original receiver, the sound quality is not going to be very good. If converted to AST there would be less background noise and your own voice would be quieter. Moving the receiver connections on the ST set as noted earlier will reduce the sidetone if it is really objectionable. Your correspondent will think you sound "tinny" with or without AST.

If you really want reasonable sound quality, you need the more modern elements.

Having said all that, I can't see any problem using the four spring AE 21 Desk Stand in an AST circuit. Whilst it is true that the later AST AE 21s, like the 1-A and similar Monophones, have a five spring hook switch, before about 1931, they used four spring hook switches. You should be able to follow a pre 1931 AE 1-A circuit.

I'm sure the IC and capacitor in the subset can be (re) arranged to suit although balance may not be perfect.

I haven't looked in detail but there will be a reason that AE changed from a four to a five spring hook switch. Whatever that reason was will be a feature of your telephone.

Regards
Jack

[unbeldi]

Here's one that can be booster ( receiver 7 to 8 ) or AST by changing one wire on the receiver 7 to 5.  Hope this helps.   stub

Although I have not drawn out the circuit diagram for this schematic, I do not believe that they actually mean that this is an AST circuit in the sense that is ascribed to the term by the work of Campbell and Western Electric.   It rather is probably a sidetone reduction circuit, as was also used by Western Electric before they introduced true AST circuits.  The Campbell AST circuit requires a three-winding induction coil.  The only two-winding AST circuit that I recall is the one used in the induction coil handset circuit by Automatic Electric in which the induction coil also served for driving the receiver diaphragm.

[unbeldi]

....

I haven't looked in detail but there will be a reason that AE changed from a four to a five spring hook switch. Whatever that reason was will be a feature of your telephone.

Regards
Jack

I believe the answer to this is that the four-point hook switch circuit produced a click in the receiver on hook switch transitions, as the receiver had no separate contact that could be closed LAST after the direct current path through the transmitter had been established.   In the five-point switch that was also used in the AE-34 having otherwise the same circuit layout, such a switch is positioned in the receiver loop to the secondary of the induction coil.

[unbeldi]

PS: here are diagrams that show these two circuits.  The first is the 4-point 1A circuit as used prior to ca. 1930, while the second is not of a #1, but of the AE-34, but I believe the circuit is identical.

(I can't find a completed version of the 5p 1A, I realized they were identical and stopped, I think.)

[Jack Ryan]

The only two-winding AST circuit that I recall is the one used in the induction coil handset circuit by Automatic Electric in which the induction coil also served for driving the receiver diaphragm.

There was a war time expedient that used a two winding IC to produce an AST effect. I haven't analysed the circuit but I think it was a Campbell option. PMG Tele No 237.

Jack

[Jack Ryan]

I believe the answer to this is that the four-point hook switch circuit produced a click in the receiver on hook switch transitions

That would be my first thought.

Jack

[unbeldi]

The only two-winding AST circuit that I recall is the one used in the induction coil handset circuit by Automatic Electric in which the induction coil also served for driving the receiver diaphragm.

There was a war time expedient that used a two winding IC to produce an AST effect. I haven't analysed the circuit but I think it was a Campbell option. PMG Tele No 237.

Jack

Can you post the diagram?


AFAIK, during WW-II apparently an acute shortage was in sidetone subsets to run old ST candlesticks, and they came up with circuits to run old revived sidetone candlesticks on AST subsets, since they weren't allowed to manufacture new telephone sets.
WR-C63.373 (I think Poplar1 posted a copy of it here on the forum at one time.)

[AE_Collector]

That makes sense that moving a lead for the receiver could be the "reduced sidetone" option for specific circumstances on a sidetone set up as opposed to a complete Anti-sidetone set up that would do a better job overall.

So I am hearing that it should be possible to connect the Type 21 (with 4 point switch hook) to a Type 32 Anti-Sidetone subset (with 3 winding coil). Tge sound quality will not be perfect but if keeping the Type 21 "original" with old receiver and transmitter, sound quality isn't going to ever be described as "perfect" by todays standards.

Terry

[unbeldi]

That makes sense that moving a lead for the receiver could be the "reduced sidetone" option for specific circumstances on a sidetone set up as opposed to a complete Anti-sidetone set up that would do a better job overall.

So I am hearing that it should be possible to connect the Type 21 (with 4 point switch hook) to a Type 32 Anti-Sidetone subset (with 3 winding coil). Tge sound quality will not be perfect but if keeping the Type 21 "original" with old receiver and transmitter, sound quality isn't going to ever be described as "perfect" by todays standards.

Terry

To explain the sidetone reduction feature of moving one wire as described, I am showing in the attached graphic four snapshots of the evolution of common battery telephone circuits.

A common battery circuit of ca. 1894 is shown in the first schematic, labeled A, commonly called the booster circuit.  It derived its name from the feature that the transmitted signal is enhanced (boosted) by having the secondary coil receiver circuit connected across the transmitter and using a capacitor to block DC from the receiver circuit.

Circuit B is an equivalent variation often encountered. In this, the receiver is simply moved to a different position in the secondary winding loop of the induction coil, so that all the electrical characteristic remain the same.

The third diagram (C) shows the sidetone-reduced variation that was established ca. 1903 and is mentioned in many AT&T Specifications and early Practices.  The only difference to circuit A is that the 'lower' receiver wire is moved past the transmitter, directly to L2, rather than being connected to the primary IC winding.  This is the same principle, I believe, that is described in the AE wiring diagram—I'll put that on the list of to-do drawings.

To complete the development to the true Campbell AST circuit, I am showing diagram D,   which is essentially the same circuit as A again, but it adds the tertiary (T) winding between the primary (P) and the secondary (S) winding, wound with opposite phase, directly across the receiver (RX).  This circuit is the foundation for all of Western Electric's anti-sidetone telephones, starting with the 202 of 1930, through the 302-series, and even the 500-series as well, albeit the 500-circuit adding some variation to the scheme, outside the scope of this little demo.

The early Automatic Electric Co. anti-sidetone circuit in the 1A and other Monophones (including the 34) is not equivalent to this WECo circuit, btw. The third winding is used differently in those sets, as can be seen from the diagrams I posted earlier in this topic.  It was not until the AE-40 appeared, that Automatic Electric switched to the WECo-equivalent AST circuit that had better transmission qualities apparently.  Therefore, AE actually used at least three different anti-sidetone circuits, the induction coil handset being the third kind.


PS: it would probably have been good to include the pre-booster CB circuit as well. It used the secondary winding only to connect the receiver, isolated from the primary circuit, which consisted simply of the transmitter and the primary winding in series across the line connections. I am not sure it was used much in the Bell territories, although I think, many European systems were based on it.  Its drawback was that it wasted a good portion of transmitter energy in the primary winding.

[Jack Ryan]

Thanks for the detailed explanation Unbeldi.

To me, the conventional ST circuit is a booster circuit (part of the transmitter energy is fed into the receiver loop which is then added by the IC back into the transmitter loop to boost it). The sidetone reduction variations simply remove this addition (the boost) so they are ST circuits but not booster circuits.

The AE circuit (in my opinion) used the wrong terminology; in that case it was not anti side tone, just less side tone.

Jack

[unbeldi]

Thanks for the detailed explanation Unbeldi.

To me, the conventional ST circuit is a booster circuit (part of the transmitter energy is fed into the receiver loop which is then added by the IC back into the transmitter loop to boost it). The sidetone reduction variations simply remove this addition (the boost) so they are ST circuits but not booster circuits.

The AE circuit (in my opinion) used the wrong terminology; in that case it was not anti side tone, just less side tone.

Jack

Yes, thanks, that is a good way to summarize it.


PS: Like AE in this case, even the BSP writers at Western Electric or AT&T at times completely goofed off and misrepresented operational principles of circuits. To mind come the 1960's explanations of the AST circuit which should better not be read by anyone. Even some of the later drawings of the 101A/B and 104A induction coils misrepresent the electrical situation, while all the previous drawings in telephone circuits did it correctly in terms of phase relations between the windings.

[Jack Ryan]

Can you post the diagram?

It is hard to identify a specific Campbell AST circuit. His paper was mathematical and analyses theoretical circuits rather than practical implementations. At the conclusion of his presentation he said:

G. A. Campbell: No questions have been raised which need any word from me. Of course, the paper, as it is presented, is a mathematical one, and no attempt has been made here to go into the physical problem, which I hope, will be presented by some one else at another time.


Years later, Spencer analysed some specific (GPO) circuits and said in his introduction:

G. A. CAMPBELL, in 1920, enumerated over half a million different anti-side-tone induction-coil circuits. For practical and economic reasons the number of these circuits suitable for use in British Post Office telephones is very limited and both the present standard transmission circuit, as used in Telephones No. 332, and a new transmission circuit used in the 700-type telephone, to be described in a future article, are based upon one particular Campbell circuit. This article summarises the important properties of the Campbell circuits and gives a simplified explanation of the way the circuit which forms the basis of British Post Office telephones works, assuming idealised conditions throughout. Some of the factors influencing the design of telephones based on this basic circuit are discussed and the relationship of the Telephone No. 332 circuit to it is shown. The fundamental equations for the idealised basic circuit are given in an Appendix.


I haven't analysed the two winding circuit myself but it has been referenced - I just can't remember where at the moment. The circuit is attached (if it is not a security risk).

AFAIK, during WW-II apparently an acute shortage was in sidetone subsets to run old ST candlesticks, and they came up with circuits to run old revived sidetone candlesticks on AST subsets

A waste of a winding but why not just ignore the balance winding?

since they weren't allowed to manufacture new telephone sets.

But new telephone sets were manufactured. It's just that their distribution was restricted.

I have 302s that are dated 1943 and are civilian sets.

Regards
Jack

[unbeldi]

Thanks for that diagram, Jack.  I seem to recall having seen such circuits also without taking much notice.

Here is the equivalent circuit drawing of that phone using my circuit style and removing the ringer, dial, and switches, which only clutter things.

As we see, this circuit is very similar to the circuit previously marked B, but in fact is a pre-booster circuit that has a tap in the receiver loop with the combination of a capacitor and a resistance from the line side across the transmitter.

Without knowing much more about the construction of that induction coil it's hard to see how this works in anti-sidetone function.  The coil appears to have two inductive windings and the two non-inductive resistance windings (totaling 550 Ω).

Does the combination of capacitance and resistance produce a phase shift in the signal introduced from the transmitter circuit to partially cancel the sidetone signal in the receiver?   What would be a typical impedance of the receiver used in this set?