Shunt designed Ampere Meters for tube applications, or other
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Meter mounting hole 38.5mm
Screw distance 32.5mm (center to center)
Screw hole inside diameter 3.3mm
Outside width 40mm
Meter height 31.5mm without meter connection mounts
Meter height 40mm including meter connection mounts
| When measuring the plate current of a tube,
it is generally not desired that the signal path will go through the ampere
meter. Reason is, that Ampere meter has a coil inside, and
any Audio signals should go through this. This is to prevent
frequency dependent effects, and other kind of distortion.
Yamamoto has found a nice solution for this. The meter is connected in parallel to the cathode resistor, and the meter has a high impedance. The nice part is, the impedance of the meter is choosen very convenient for the end-user. It is choosen in such a way, that the series resistor you need is exactly 100x the Cathode resistor of the amplifier. Like this you need to make no special calculations, and the meter is always calibrated correct. Here is some example to show how the series resistor is found. Suppose the cathode resistor is 1000 Ohms. What you take now, is a series resistor which is 100x larger, so 100kOhms. Automatically the meter is calibrated correct, regardless if you take a 60mA, 100mA or 150mA meter. They always the correct current. What is also good to know, is by this method the meter has better short circuit protection, as when put directly in the current path. If by any mistake you make a short circuit, the cathode resistor will absorb the energy, not the meter |
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| In series with the meter must be a resistor, to adapt for the value of the cathode resistor. This resistor is not be supplied with the meter, because the resistor value depends on the actual cathode resistor used. The resistor value is 100x the cathode resistor value, for the 100mA meter. (150x for the 150mA meter, etc.) The meters are extremely precise, and are more an "instrument" rather than just a meter only. |
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Another nice option is to use one meter, and just switch it from one channel to another, as done here with the flagship Yamamoto A06-02, the AD1 amplifier. |
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These are the bronze meter cover rings. The mounting holes are the same as for the meter. It is also possible to use the meter without the bronze cover rings. The meter by itself has a nice silver paint finish. |
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Available Scales: |
50mA |
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