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This page displays photos of 1948, 49 and 50 -dated components submitted by collectors. Based on documentation found to date, sets are grouped as follows: Pre-production sets -- made in 1948 or earlier. Early Production sets -- made before October 1949, some used in the 1949 field trial. Production sets -- made in October 1949 and later. Photos of a 1950 set are used on this page. So far, we have photos of only one pre-production set and have info on only a few 1949 sets. There are probably more variations that were made that are yet to be discovered. This page is a work in progress. Please send comments, additions and corrections. Photos: D177001 by Dan Robinson, early 1949 set in the Museum of Communications (Seattle) by Greg Goebel. Last update: 22 March 2020 |
| Base |
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1948 Base (D177001 - Pre-production)
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1949 Base (Early Production)
 1950 Base (Production)  Cutouts in dial mount are
to hold terminal strips for optional future features.
Similar slots in the hookswitch mount are for an exclusion switch mount. These greatly increase the flexibility of the set, reducing inventory and making it possible to easily convert from one model to another during refurb. |
| Bottom Plate |
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1948 Bottom (D177001 - Pre-production)
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1949 Bottom (Early Production)
Drilled for mounting future options: tube for party line ringing, and line switch for 2-line version. Rivited feet.  1950 Bottom (Production)  Model number added and
date format simplified.
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| Dial |
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1948 D-177008 Dial (D177001 set - Pre-production)
 Included an inspection "window" on the front to watch the gear in motion. Eliminated before production. 
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1949 (Early Production) and 1950 (Production) 7A
Dials were the same,
including the "Operator" text circling the 0 digit on the dial plate. 
Dial components were
rearranged, probably to make the footprint small enough to
use the same subassembly in the 3-inch #6 dial, which was
introduced after the #7 dial.
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The 3" 6A dial (4-54) and
the 4" 7A dial (4-53) apparently use the same gear
arrangement.
(Differences are due to the slightly different camera angles.) Casting and contact subassemblies are obviously different.  Paul Schreiber noted the different exit positions on the wires on the 7A dials from 1949 and 1953 above. The later 7As had a nearly straight line path from the contacts, making manufacturing simpler and (presumably) cheaper. The transition appeared in early 1950. |
| Housing |
| 1948 Housing (Pre-production) [Photo Wanted] |
1949 (Early Production) and
1950 (Production) housings were the same. Circular stiffener in lower right is for a hole for the (future) line switch. Switchhook plungers were changed from clear to black. |
| Ringer | |
1948 D-177006 Ringer (D177001
set - Pre-production) Note: Only 1 screw attachment point - changed to two (below). |
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1949 C2A Ringer (Early Production)
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1950 C2A Ringer (Production)
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| Three
grommet
ringer supports pressed into base were replaced by 2
captive grommets |
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| Equalizer | |
1948 D-177018 Equalizer
(D177001 set - Pre-production) |
Internal Equalizer Components. |
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1949
(Early Production) and 1950 (Production) 311A
Equalizers were the same
 (Bill Geurts photo) |
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| Varistor
screw
attachment to can was eliminated. |
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| References | |
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Date
Source*
Topic
49/02 IB News 500 coming “Leak” – “still in design stage” 49/03/16 BTL Press Release – New Telephone Instrument 49/04 NE TelTopics - New Telephone Instrument, p 15 49/05 BLR - New Telephone Instrument 49/05 IB News - New Telephone Instrument 49/05 PacTel Mag - New Telephone Instrument 49/05 BTL Notes on Discussion at the Conference of BS Lecturers 49/06 Popular Science New Phone Rings Loud or Soft, p 108. 49/12/12 Life Mag New Telephone, p. 67 (also see p. 128 Dooner, yellow) 49/12/29 News Letter Field Trial in St. Louis (AT&T Archive) 50/02 BLR Cover Photo (Pre-production set) 51/01 BSTJ “The Ring Armature Telephone Receiver,” p 110 51/04 BSTJ “75 Years of the Telephone,” p215 51/04 BSTJ “An Improved Telephone Set” (500), p 239 Trials, 48 & 49, pre-production sets, 4000 in 49 51/aut BTM “A New Telephone” (500), p 164 52/05 BLR “Dial for 500 Type Telephone Set” (7A), p 211 53/03 Ohio Bell 510 in production, p 42 53/05 BSTJ “An Improved Circuit for the Telephone Set” (425B net), p 611 54/03 WE Mag p.7 (Manufacturing Locations) 55/sum BTM "Designing the Telephone" (from Dreyfuss book) Designing for People, Henry Dreyfuss, 2003, pp 106-7. Old Time Telephones, Ralph Meyer, 2005, p 88, p121 (dialing dots). Singing Wires, Jan - Aug 2009, Series on 500-series history. Singing Wires, Nov 2004, Henry Dreyfuss. * Source Abbreviations: BLR - Bell Laboratories Record BSTJ - Bell System Technical Journal BTM - Bell Telephone Magazine Other sources are Bell System press releases and employee magazines. e.g. IB - Illinois Bell, NE - New England Tel, WE - Western Electric Date format: YY/MM/DD, or YY/season |
