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
(Photo from Pacific Tel Magazine, May/June 1949.)
Marked D-117001, undated.
(Best guess based on research to date. Watch for updates.)
Internal components similar to the patent drawings.
Aluminum dial mount. Plastic fingerwheel.
Bell coil wrapped in olive cloth (like 302s B1A).
Aiming dots, visible through the fingerwheel holes, were added during the development process to help improve dialing speed and accuracy.
Field Trial of 50 pre-production sets. (BSTJ*, 4/51)
*Bell System Technical Journal
|1949, Early production
No model number marked, dated on front edge of bottom plate.
Internal components were modified to satisfy manufacturing and service considerations. Metal fingerwheel.
Field Trial of 4000 early production sets in 10 locations, including Manhattan, Staten Island, Chicago, St. Paul, St., New Orleans, Los Angeles and San Francisco. (BSTJ, 4/51) Also St. Louis. (From an internal Bell System memo in the AT&T Archives)
between Pre-Production and Production Sets
These features shown on the patent drawing were changed before the "early production" sets were made:
Note: It may help to open this drawing in a seperate window for reference while you scroll through the following photos.
*Component serial numbers for detailed tracking and control were eliminated on production sets.
1948 Base (D177001 - Pre-production)
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.
1948 Bottom (D177001 - Pre-production)
1949 Bottom (Early Production)
Drilled for mounting future options: tube for party line ringing, and line switch for 2-line version.
1950 Bottom (Production)
Model number added and date format simplified.
1948 D-177008 Dial (D177001 set - Pre-production)
Included an inspection "window" on the front to watch the gear in motion. Eliminated before production.
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.
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.
|1948 Housing (Pre-production)
|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.
|1948 D-177006 Ringer (D177001
set - Pre-production)
Note: Only 1 screw attachment point - changed to two (below).
1949 C2A Ringer (Early Production)
1950 C2A Ringer (Production)
ringer supports pressed into base were replaced by 2
|1948 D-177018 Equalizer
(D177001 set - Pre-production)
||Internal Equalizer Components.
1949 (Early Production) and 1950 (Production) 311A Equalizers were the same
(Bill Geurts photo)
attachment to can was eliminated.
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
55/sum BTM "Designing the Telephone" (from Dreyfuss book)
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