American Bosch 28 Schematic

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Product Information:
Model:28
Manufacturer:American Bosch (United American Bosch & Fred M. Link)

Schematics Content:

Page 1:

American Bosch Magneto Corp.

Model 28-29 AC
Schematic Wiring Diagram
25 - Grid Leak 3 megaohms
26 - Grid condenser .00025 mfd.
27 - Plate Resistor 50,000 ohms
32 - External Cond. .00015 mfd.
36 - By-Pass Condensers .5 mfd.
37 - By-Pass Condenser 1. mfd.
38 - By-Pass Condenser 1. mfd.
43 - By-Pass Condenser .002 mfd.
87 - Volume Control 500,000 ohms
102 - Filter Condenser 2 mfd.
103 - Filter Condenser 4 mfd.
107 - Bias Resistor 1500 ohms
110 - Bias Resistor 300 ohms
111 - "B" Resistor 5,000 ohms

Model 28 - 29
Revised Wiring Diagram

American Bosh Model 29
Line Voltage 115 - 115 Volt Tap

American Bosh Model 28
Line Voltage 115 - 115 Volt Tap

Page 2:

Page '58

AMERICAN BoscH MAGNETO CORP

or" 0m Onto

POWER TRANSFORMER

The power transformer "100" is enclosed in the transformer can "98." Since the transformer is completely sealed, it is necessary to replace the entire unit.

The transformer has a single primary Winding and five secondary windings, two of which have center taps. The colors of these leads, together with their points of attachment to the resistors and other parts, are given in the following paragraphs.

1.5 Volt Winding "114": Supplies filament current for RF and lst AF tubes (7, 8, 9, 11). The two leads from this winding are red and connect to the two end terminals of resistor "109."

22 Volt Winding "115": Supplies filament current for the detector tube and dial lamp (10 and 16). The two leads from this winding are black and connect to the two end terminals of resistor "108."

5 Volt Winding "116": Supplies filament current for the two push-pull stages (11 and 12). The two leads from this winding are blue and connect to the two end terminals of resistor "106."

Single Brown Lead (Primary Lead) Cotton Covered: To one of the main switch "17" leads.

Twisted Leads (Primary Taps): Black with red tracer - to tap switch (15). "105" tap. Black to tap switch (15), "115" tap. Black with yellow tracer - to tap switch (15), "125" tap.

Brown Twisted Leads (Plate Winding "118"): To plate contacts (small holes) of socket "14."

Brown Cable (Filament Winding "ll7"): To filament contacts (large holes) of socket, "14."

Single Black Lead: To terminal "119" of strip "112." This lead is the center tap oi rectifier filament winding "117."

Single Green Lead: To ground connection. This lead is the center tap of the rectifier plate winding "118"

FILTER CAN

The Filter Can "99" contains the two Filter condensers "102" and "103," and the filter Choke coil "101." These three units are sealed in the cans making it necessary to replace the entire filter can if any of these units become defective.

There are five leads from the filter can, connected as follows:

Black Fabric Covered Wires: These leads come from the choke coil "101" and connect to terminals "119" and "122" of terminal strip "112." These two leads are interchangeable.

Black Lead: This lead comes from filter condenser "103" and connects to terminal "119."

Blue Lead: This lead comes from filter condensers "102" and "103" and connects to ground terminal "123".

Red Lead: This lead comes from filter condenser "102" and connects to terminal "122."

Filter Can Replacement
1. Unsolder the five leads of the filter can at their point of connection to the terminal strips.
2. Remove the 4 holding screws "125."
3. Mount the new can in place.
4. Connect the wires as indicated in the preceding paragraph.

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