Yamamoto Precision Panel Meters
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
UNFORTUNATELY THESE METERS ARE NOT MADE ANY MORE. What we have for sale is only what is left in stock here. This is a pity, because the dimensions are from old USA meters, and the Chinese meters are larger dimensions.
Yamamoto Anode current meter, for auto bias only
Please take a moment time, to understand those intelligent meters, because they are not like the usual meters. When measuring the Anode 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 would be disturbed by this coil. The intention of these meters is to prevent frequency dependent effects, and other kind of interference. Besides, precision of low cost devices is not very good.
Yamamoto has found a nice solution for this. The meter is connected in parallel to the cathode resistor, and the meter is high impedance. This method is really genius. The meters gets a series resistor, which you can conveniently calculate. Besides, by this method the device is short circuit protected. If by any mistake you make a short circuit, the cathode resistor will absorb the short circuit energy, and not the meter
Calculate series resistor (pdf)
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. 50x for the 50mA meter, 150x for the 150mA meter, and 300x for the 150mA meter.
The meters are extremely precise, and are more an "instrument" rather than just a meter only.
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.
Meter Hardware
The meter is pictured here with the mounting flange, though it can be used also without also.
The advantage of the flange is two:
- No visible screws in the deck plate.
- The hole in the deck plate can be unprecise, as it will be covered fully. You can file it by hand, and the appearance is still professional.
