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This kit includes following components:
One KPB-02 Crystal Radio Impedance Matching transformer.
Two 1 X 12 rotary switch includes two knobs.
One 500K Ω potentiometer with a knob and a 0.1 uF capacitor for Benny circuit.
Two ¼” mono speaker output sockets.
Four banana sockets and plugs.
One 4-7/8 X 3-1/2 X 2 inch plastic box
You only need to prepare some strong tape and appropriate size of screws & nuts to hold the transformer on plastic box, and some insulated wire for circuit wiring. The rotary switchs only have 12 positions, so on the transformer you can choose 12 Impedance taps for input (for example from 200KΩ to 150Ω) and 12 Impedance taps for output (for example: from 40KΩ to 32Ω, 20KΩ to 16Ω, 10KΩ to 8Ω, 5KΩ to 4Ω).
You also can order the KPB-02 Crystal Radio Impedance Matching transformer only in this link:
Many crystal radio fans know the Bogen T725 audio matching transformer. The builders of quality crystal radios have found them useful as a matching auto transformer between the diode output and headphones. But the maximal impedance of T725 only can reach 40KΩ.
You may need higher impedance auto transformer if you want to build a better quality crystal radio. Some crystal radio fans in China are design, test and produce a new autotransformer for this target.
This transformer has 18 terminals , can be match from 200KΩ to 4Ω by 17 steps. They use high permeability ferrite magnetic core and easy to get plentiful inductance with this small volume of core. The crystal radios output only have small electric current (from microampere to few milliampere), so we don’t have to worry about magnetic saturation in magnetic core.
The specs of this transformer are:
Dimension: 4 X 3.5 X 3 cm
Weight: 104 gram
Electrical parameter:
Pin No. -- Impedance -- DC resistance
14 -- 200 KΩ -- 3.55 KΩ
13 -- 100 KΩ -- 2.04 KΩ
12 -- 40 KΩ -- 810 Ω
11 -- 20 KΩ -- 479 Ω
10 -- 10 KΩ -- 253 Ω
9 -- 5.0 KΩ -- 170 Ω
8 -- 2.5 KΩ -- 113 Ω
7 -- 1.5 KΩ -- 80 Ω
6 -- 800 Ω -- 52 Ω
5 -- 500 Ω -- 37 Ω
4 -- 300 Ω -- 24 Ω
3 -- 150 Ω -- 12 Ω
2 -- 64 Ω -- 6.7 Ω
White wire -- 32 Ω -- 4.1 Ω
Blue wire -- 16 Ω -- 2.2 Ω
Yellow wire -- 8 Ω -- 1.4 Ω
Red wire -- 4 Ω -- 1 .0 Ω
1 -- 0 Ω -- 0 Ω1 -- 0 Ω -- 0 Ω# E8 K: `
We compare the Bogen T725 and this ferrite magnetic core transformer in an actual measure, with 0.3V 1000Hz sine wave signal input at 40KΩ tap and a 300Ω resistor at 300Ω tap, the result shows the conversion efficiency are 83.5% and 94%. This small ferrite magnetic core transformer is 10.5% better than Bogen T725.
For more information about this transformer, please use key word "KPB-02" to search articles in theradioboard.com
Please e-mail any questions you may have before you order.
| MPN | Does Not Apply |
| Brand | Unbranded/Generic |
| Compatible Brand | Universal |
| Country/Region of Manufacture | China |
| UPC | Does not apply |
| Type | Crystal Radio |