Belmont Model 678 Auto-Radio Set
Radio Service Data Sheet
August 1940 Radio-Craft

August 1940 Radio-Craft [Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Craft, published 1929 - 1953. All copyrights are hereby acknowledged.

Unlike even the vacuum tube type AM radio in the dashboard of my parents' car in the early 1960s that were self-contained units, even earlier radios designed for cars and trucks had their bulky electronics mounted under the sea or in the trunk, with a remote volume and tuning control mounted in the dashboard. That greatly complicated the installation as well as the design of the radio. This circa 1940 Belmont Model 678 Auto-Radio is a prime example. Note the unique cylindrical shape of the radio chassis, and that the remote control is a pushbutton assembly with rotating knobs for tuning and volume. Operating from a 6 volt DC car battery (12 volts came later), these radios required a "vibrator" circuit to convert DC to AC (and back to a higher level DC) in order to transform to a couple hundred volts for the plate voltage of the tubes.

Belmont Model 678 Auto-Radio Set Radio Service Data Sheet

6-Tube Superhet.; 6-Button Automatic Remote Tuner Unit; Automatic Volume Control; Range 535 kc. to 1,565 kc.; Synchronous-Type Vibrator; Single Stud Mounting.

Fig. 1. Complete schematic diagram of the Belmont model 678 auto-radio receiver.

Fig. 2. Chassis view showing locations of trimmers and components.

Fig. 3. Bottom view of remote tuner

Fig. 5. Belmont auto-radio model 678. Note Remote Tuner at right.

Alignment Procedure

Turn volume control to maximum for all adjustments. Connect radio chassis to ground post of signal generator with a short, heavy lead. Connect dummy antenna in series with generator output lead;- 0.1-mf. for the I.F. band and a 125 mmf. for the broadcast band. Use an output meter across the primary of the output transformer. Allow chassis and signal generator to heat up for several minutes.

I.F. Alignment

Feed a 465-kc. signal to the grid of the 6SK7 I.F. tube. Set dial at 1,400 kc. Adjust trimmers C19 and C20 for maximum output. To align this output I.F. unit without using cathode-ray oscilloscope, a 10,000-ohm resistor must be shunted across the diode tuned circuit as indicated by points X and Y on the schematic (Fig. 1) and in Fig. 4. Trimmer C19 is identified by a red dot on top of the I.F. can.

Fig. 4. Bottom view of chassis giving socket voltages.

After alignment of these 2 trimmers, remove the 10,000-ohm resistor and align trimmer C21 for maximum output. Do not readjust trimmer C19 or C20 after the resistor has been removed. Shift the signal generator lead to the control-grid of the 6A8 and adjust trimmers C14 and C15 for maximum output.

Broadcast Band

Feed a 1,565-kc. signal to the antenna lead with the set dial adjusted to 1,565 kc. Adjust trimmer C5 for maximum output. Reset the dial to 1,400 kc. and adjust trimmers C1 and C3 for maximum output using a 1,400-kc. test signal. Finally, reset the dial to 600 kc. and adjust trimmer C2 using a 600-kc. test signal in the antenna lead. Maximum gain for this adjustment depends on the capacity of the antenna system of the car in which the radio receiver is installed.

Power consumption is 7.7A. at 6.3V. No suppressors required on the spark plugs; only a distributor suppressor is needed. The output I.F. coil has 3 tuned circuits giving superior band-pass qualities and selectivity as compared to the conventional 2-tuned-circuit coils. Antenna, R.F. and oscillator circuits are permeability tuned, offering automatic tuning applications that are both accurate and stable. The entire coil assembly is mounted in the Remote Tuner control head being connected to the oscillator and R.F. circuits by an R.F. transmission cable.

The R.F. oscillator, and I.F. and A.F. amplifiers, including the power supply, are contained in the speaker case.

This unit has been designed to facilitate servicing.

Radio Service Data Sheets

These schematics, tuning instructions, and other data are reproduced from my collection of vintage radio and electronics magazines. As back in the era, similar schematic and service info was available for purchase from sources such as SAMS Photofacts, but these printings were a no-cost bonus for readers. There are 227 Radio Service Data Sheets as of December 28, 2020.

• AMRAD Model 81 "Bel Canto"
• GE Model 250 Radio Service Data Sheet
• Hoffman Model A300
• Emerson Model 505
• Olympic Models 6-501, 6-502, 6-503
• Radiola Models 61-5, 61-10
• Farnsworth Models ET-060, ET-061, ET-063
• General Electric Model 321
• Garod Model 6AU-1
• Truetone Model D4620
• Westinghouse Model H-148
• Wards Models 54BR-1501A, 1502A
• Majestic Models 8S452, 8S473
• RCA Models Q22A, Q32
• Zenith Model 5G003ZZ
• Mantola Models 92503 and 92504
• Emerson Model 508 Series 8-7434351 and Up
• Belmont Model A-5D118
• Wards Model 74BR-2707A
• Crosley Model 56TP-L
• Admiral Model 7C60 Chassis 6B1
• 336 Belmont Radio Model 6D111, Series A
• 333 General Electric Models 100, 101, 103 and 105
• RCA Victor Models 54B1, 54B-N, 54B2, 54B3 Radio Data Sheet 335
• National Union "Presentation" Radio Model G-619
• Zenith Radio Models 8H032, 8H033, 8H050, 8H052, 8H061
• General Electric Farm Radio Model 280
• Admiral Model 6RT44-7B1
• Montgomery Ward Airline Model 04BR-1105A Radio
• Belmont Model 678 Auto-Radio Set
• Sentinel Model 217-P Portable Radio Set Radio
• Remler Model No. 36 Dual-Wave Auto-Radio
• Stromberg-Carlson No. 82 All-Wave Receiver
• Majestic A.V.C. Model 290 Chassis
• FADA 9 Tube Model 190 "Metal" All-Wave
• RCA Victor Models 9T and K2 9-Tube, 5- to 566-Meter
• Motorola "Golden Voice" Model
• RCA Victor Model H-6
• Simplex Model TA
• Automatic "Magic Eye" Model A1
• Silvertone Models 4488 and 4588 (Chassis No.101412) and 4488A and 4588A (Chassis No. 101412A)
• RCA Victor Model M109 "De Luxe" 7-Tube Auto-Radio Receiver
• Crosley Model 6625 6-Tube 3-Band Receiver
• International Model 77 Series 7-Tube Dual-Band Receiver
• Belmont Model 6D121
• General Electric Models 60, 62
• Admiral Model 7C64
• Radiola "28" Super and "104" Power Speaker
• Sonora Model TW-49
• Stromberg-Carlson Models 1020, 1120, Series 10
• Air King Model 4604D
• Sparton Models 526, 526X, 526PS
• Truetone Model D2624
• Admiral Models 6EI, 6EIN
• Detrola Models 571A, 571B
• General Electric Model 250
• Howard Model 920
• Colonial Model 652 5-Tube Broadcast-Short-Wave
• Fairbanks-Morse 9-Tube All-Wave Model 91
• International Model 500 5-Tube Dual-Range Battery
• Emerson Model 678 "Auto-Dynamic" 5 Tube
• Stromberg-Carlson Nos. 230 and 231 Series
• Atwater Kent Model 649 All-Wave
• Howard Model G-26, and "Airplane 4" Model AA25
• Montgomery Ward "Airline" Series 7GM 7-Tube High-Fidelity Receiver
• RCA Victor Model T5-2 5-Tube, 2-Band A.C. Superheterodyne Receiver
• Majestic "Models 50," "51" and "52"
• Bremer-Tully Model 7-70 and 7-71
• General Electric Model M-49 4-Tube Radio-Phonograph Dual-Wave Superheterodyne
• RCA-Victor Radiola "Superette" Model R7 Superheterodyne
• Crosley Model AC-7 and AC-7C
• Westinghouse "Columnaire" Models WR-8 and WR-8-R (Remote Control)
• Characteristics of Metal Tubes - and Other "Octal" (8-Prong) Base Types
• Kolster K20, K22, K25, K27 and K37 Six-Tube Receivers
• Stromberg-Carlson Nos. 62 and 63, 8-Tube High-Fidelity Chassis
• RCA Model 103, 4-Tube A.C. Compact Dual-Wave
• FADA "Special" Model 265-A and FADA "7" Model 475-A
• General Electric Model C-62 6-Tube Battery
• Emerson 5A Automotive
• Zenith 666 Automotive
• Motorola 100 Automotive
• Crosley Roamio 4-A-1 Automotive
• American-Bosch 524A Automotive
• Crosley Model 1316 (in Model 167 Console)
• RCA Victor "High-Fidelity Electrola," Model R-99
• AMRAD Model 81 ("Bel Canto" Series) Receiver
• Fada 103 Fadalette, Stewart-Warner Series 108, DeWald 54 Dynette Sets
• RCA Victor R-27 and Philco 53 Ultra-Midget A.C.-D.C. Radio Receivers
• Majestic Models Fairfax and Sheffield 8-Tube
• Stromberg-Carlson No. 29, 9-Tube Superhet
• International Kadette Model 400 4-Tube Battery-Operated Superhet
• RCA Victor Model 5M 5-Tube Auto Superhet
• Majestic Model 11 Short-Wave Converter
• Silver-Marshall Model 727-DC Battery-Operated Superheterodyne
• RCA Victor Model VHR-307 Home Recording - Phono-Radio Combination
• Delco 32-Volt Radio Receiver Chassis Models RA-3, RB-3 and RC-3
• Majestic Chassis Models 380 A.C. T.R.F., and 400 A.C.-D.C. Superheterodyne
• General Motors S1A, S1B
• Admiral Model 7C63, Chassis 7C1
• Westinghouse Model H-133
• Arvin Models 150TC, 151TC
• Kadette Model 90 Duplex
• RCA-Victor "Magic Brain" Model 281
• Grunow 11A Chassis 11-Tube All-Wave Superheterodyne
• Sears, Roebuck & Co., Silvertone "Rocket" Models 6110 and 6111
• General Electric Model GD-52
• Zenith Models 6D302, 6D311, 6D326, 6D336, 6D360
• Allied Radio, Knight Model E10913
• Arvin Model 140P
• Emerson Models 501, 502, 504
• Crosley Model 56TD-W
• Hoffman Model A500
• Stewart-Warner Model 9003-B
• Zenith Models 6D014, 6D029
• Coronet Model C-2
• Sparton Models 7-46, 7-46PA, 8-46, 8-46PA
• Stewart-Warner Models 9001-C, D, E, F
• Zenith Models 5D011-5D027
• Bendix Models 636A, C, D
• ECA Model 108
• International Model 66 and 666, 6-Tube Superhet
• Ford-Philco Radio, Model FT9, 6-Tube Auto-Radio Receiver
• Howard Explorer Model W Deluxe 19 Tube All-Wave Superhet
• RCA Victor Portable Table Electrola Model R-95
• Atwater Kent Model 305Z 5-Tube 32 V. D.C. Superhet
• Kadette Jewel Model 40 Chassis 3-Tube Ultra-Midget Receivers
• General Electric Model N-60 6-Tube Auto Superheterodyne
• Sparton Model 40 6-Tube T.R.F. Automotive Receiver
• Clarion "Replacement" Chassis, Model AC-160 A.V.C. Superheterodyne
• Emerson Models 20A and 25A
• General Electric K-40A
• Pilot Model B-2
• RCA-Victor Radiola Model M-30 Automotive Radio
• Motovox Models 10A All-Electric and 10E Battery-Operated "Moto-Tetradynes"
• Kennedy Superheterodyne Short-Wave Converter
• RCA Victor Model R-78 B1-Acoustic 12-Tube
• Philco Model 15 Series, 11-Tube Superheterodyne Chassis
• Zenith Challenger Model 740
• Sparton Selectronne Receivers Models 1068 and 1068X
• Fada Model 155 Super Fadalette A.C.-D.C. Set
• Clarion De Luxe Models AC-280 and 25-280
• Crosley Model A-157 (River Roamio) Auto Radio
• Philco Model '37-116 Codes 121 (Shadometer) and 122 (Dial Tuning)
• Arvin Model 28
• Philco Model 818
• Fada Model 266 Motoset
• Bosch Models 736, 737, 738
• RCA-Victor Model 15U, Radio-Phonograph
• Sparton Models 566 ("Bluebird" Mirror), A.C.-D.C. 5-Tube 2-Band Midget Superhet
• Atwater Kent Model 776 6-Tube Auto Radio
• Stromberg-Carlson No. 61 4-Band 7-Tube A.C.-D.C. Receiver
• Arvin Model 182TFM
• Crosley Model 58TK
• Westinghouse Model H-165
• General Electric Models G-105 and G-106
• Silvertone "F," "FF," "G," "H," and "J"
• Stewart-Warner Model 03-5A1 to 03-5A9 (Chassis 03-5A) Senior Varsity Radio
• Radiola Models 61-6, 61-7
• Westinghouse Models H-104, H-105, H-107, H-108
• Farnsworth Models EC-260, EK-262, EK-263, EK-264, EK-265
• United Models 980744, 980745
• Stewart-Warner (R-127 Chassis) Models 1271 to 1279 All-Wave
• ERLA Model 4500 Dual-Wave T.R.F. 4-Tube A.C. Receiver
• Clarion No. TC-31 5-Tube A.C.-D.C. Superhet.
• Detrola Model 105C 5-Tube Dual-Band A.C.-D.C.
• Zenith 6-Tube All-Wave Chassis No. 5634
• RCA Victor Model 261, 555 to 107 Meter
• Philco Model 38-116; Code 125
• Stewart-Warner "Ferrodyne" Chassis Model R-136
• American-Bosch Model 43OT 5-Tube 3-Band Superheterodyne
• RCA Victor Model C9-4 9-Tube 3-Band Superheterodyne
• Kennedy "Model 826B" Combination Receiver
• Steinite 50-A and 102-A
• Pilot Model 63 All-Wave 6-Tube Superheterodyne
• Stromberg-Carlson No. 69 4-Tube All-Wave Superhet. Selector (Converter)
• RCA Victor Model 102 4-Tube A.C.-D.C. T.R.F. Receiver
• Bosch Models 60 and 61
• Atwater Kent Models 30, 33, 35, 48 and 49
• Crosley Model 120 Senior Superheterodyne (Pliodynatron) Chassis
• Columbia Screen-Grid 8 Receiver
• General Electric Models A82 and A87, 8-Metal-Tube All-Wave A.C. Superhet.
• Colonial 31 and 32 D.C.
• Zenith 5-Tube Triple-Wave Chassis nos. 5508 and 5509
• Remler Model 46 ("Scottie")
• General Electric FA-60 and FA-61
• Stewart-Warner Series 900
• Howard Model B-5 (715), Series 1 and 2 (Sheaffer Radio-Clock-Pen Desk Set)
• Ford-Philco Car-Radio Models F-1440 and F-1442
• Brunswick Model 31 Combination Radio and Panatrope
• Emerson Models 38, 42 and 49, 6-Tube Dual-Wave (Chassis U6)
• General Motors Chevrolet No. 601574 Automotive
• RCA Victor M-104 (and M-108) Automotive
• Arvin-Ford 17-A Automotive
• Westinghouse Model WR 207 & WR 208 5-Tube Dual-Band Superheterodyne
• Radiolas "Super VIII" (AR-810, "Semi-Portable" (AR-812), 24 and 26
• Howard Model 45 A. V. C.
• Majestic Model 25
• Galvin Motorola Model 61
• Arvin Model 6
• Admiral Models 7T06, 7T12
• Garod Model 5A1
• Hoffman Model A301
• Knight Model E10716 Battery Portable
• Arvin Models 555, 555A, 552N, 552AN
• Grantline Models 605, 606
• Truetone Model D2616
• Belmont Model 5D128
• Arvin Models 444, 444A
• International Kadette Model 1019
• Stewart-Warner Models 97-561 to 97-569
• General Electric Model 280
• Zenith Models 5R080, 5R086
• Truetone Models D1747, D1748
• Crosley Roamio Automotive T.R.F. Models 90, 91, 92
• Crosley Roamio Automotive Superheterodyne Models 95, 96
• Wells-Gardner Series 062
• Emerson Model AZ-196
• Belmont Model 5P19
• Crosley Fortyfive
• Crosley Model 56FC
• Emerson Models 507, 509, 518, 522, 535
• Garod Model 6AU-1
• General Electric Models 219, 202, 221
• Crosley "Chairside" Model 567
• Belmont Model 408 Battery "Farm"
• Wards Model 74BR-1055A
• Farnsworth Models EK-081, EK-082, EK-083, EK-681
• Philco Model 200-X Radio
• Admiral "Aeroscope" Models 161-5L, 162-5L and 163-5L
• Philco Model 59, 4-Tube A.C. Midget Superheterodyne
• Zenith Farm Model 6V 27, 6-Tube Superhet
• Ward 10-Tube All-Wave High-Fidelity Superhet, Series ODM
• Philco-Packard Deluxe
• Canadian Westinghouse Model 175
• Crosley Model 1155
• Philco Models 39 and 39A
• Arvin Model 35 8-Tube Car-Radio
• Hetro Air-Ace Series M
• Westinghouse Models H-161, H-168, H-168A
• Garod Model 5A4
• Arvin Models 152T, 153T
• Belmont Model 5240
• Mantola Models 92505, 92506
• General Electric Models 102, 102W, 107, 107W, 114, 114W, 115, 115W
• Crosley Model 555 (A.F.M.)
• Crosley Model 515 (Fiver)
• Crosley Model 425 (Travo)
• Firestone-Stewart-Warner Model R1332
• Fairbanks-Morse Model 81 "Farm" Set
• Clarion Model 423, 470, 471, 472, 480
• International Radio Corp. Model 90
• Belmont Model 578 Series A