New Vs. Old subset

[Jack Aman]

Question for the group:  I have an old D1 202 with a period-correct subset.  The phone is one of my "daily drivers" and actually works very well.  I have been given an old but new (unused) 685A subset.  Will my D1 provide better sound quality or any other performance improvement if moved to this newer subset? 

Thanks in advance for help and Happy New Year to all.

[Phonesrfun]

The question I have is what is a "period correct" subset?  I presume it is something like a 634? If your existing subset is a 634 or equivalent antisidetone subset, you won't really see much if any difference.  Besides, to take advantage of the automatic line compensation in the 685A, you would need to do a little rewiring and use a 5-conductor line cord. 

But, on the other hand, you will never know for sure until you try.

[dsk]

You do not usually wear out a subset, the so if the "new one has identical components, it should perform "as new". Still it may even be minor differences in two units made the same day so as Bill stated you have to try.  The critical part is the transmitter capsule. 

dsk

[unbeldi]

The most critical components w/r/t sound quality are the transducers that convert between electrical energy and mechanical energy, i.e. the transmitter and the receiver. These establish essentially all the parameters for frequency response and bandwidth, providing the significant aspects for "audio quality".

The principal underlying electrical operating principle did not change from anti-sidetone induction coil subscriber set and (so called) network-type units. Although the components in the network types were slightly retuned to the specific impedances of the new 500-style transducers, the differences are small enough that they really don't effect audio quality in otherwise equally well operating stations.  But as already mentioned, sidetone balance can be effected if the sidetone conditions, especially surrounding noise, at the operating stations are severe.  The networks use dynamically varying resistances (varistors) in the balancing circuits, rather than the statically dimensioned components in older subscriber sets.

Only the local-battery 307 type telephone and some 400-series subscriber sets had some adjustment provisions for line impedance balance. Other telephone manufacturers than Western Electric at times used manually variable resistances for adjusting the line balance, but this had to be adjusted by the installer for each installation.
The Bell System Practices do specify various service arrangements in which both types of transducers, pre-500 (F1/HA1) and 500-style (T1/U1), were used on induction coil telephones, so there is a basic compatibility between them.

[Jack Aman]

Thanks everyone for the kind assistance.  The subset in use is a 684-BA by the way.

[unbeldi]

The 684BA was among the subsets documented in the BSPs of 1931, and is certainly a ''period-correct'' subset for a 202-type telephone.  Originally it had the high-impedance 78J type ringer (4300 ohm), but later a B-type ringer (4600 Ω) was used, best known from the 302 telephone.

Which kind of ringer does yours have?

AFAIK, the connection of a 202 or 211-type telephone to a 685A subset using only a four-conductor mounting cord is nowhere documented in the BSPs. The BSPs of the late 1950s—the 685A was introduced in 1955—and thereafter only describe using a five- or six-conductor mounting cord.  Of course, at the time there was no reason for them to use only a four-conductor cord, because (a) they had no incentive to preserve historical configurations as collectors do, and (b) it made no sense to revert to older technology without line balance.

However, it is possible to preserve the original four-conductor cloth mounting cords on 202s and still hook them up with a 685A subset in a manner that requires no modification at all to the desk set wiring.

By my experimentation, this actually does have one benefit. It provides perceptively enhanced listening volume for the user of the set. I can't say the audio quality is any better, but often it is desirable to have a little extra volume as the old receivers (as well as the transmitters) were indeed not as efficient as the newer types (and very likely as hearing degrades with the age of the listener).  I haven't established that the person on the other end actually perceived any difference, it appeared not so.

I think the reason for this is that in a four-wire arrangement, the instrument uses only one-half of the primary induction coil, therefore achieving twice the transformation ratio between primary and secondary/tertiary windings. As we know the human ear has a logarithmic response for which a doubling of output power is necessary for small increase in perceived volume.