Press the "melt" button, the Crucible metal no redness, ammeter and anode and grid no current ammeter, measurement of anode DC voltage is normal. First check whether the oscillator circuit breaker. Block condenser Ca regular circuit breakers, turning AC circuit without oscillation. In addition, in order to prevent high frequency radiation, resonant capacitor l, c, feedback loop and grid resistance Rg, bypass capacitors Cg, are enclosed in a shielded metal boxes are more prone to failure. Open the lid if the gate with adjustable resistance Rg is open circuit (electronic cannot be released on the ceramic rods, leading to negative gate voltage of the tube cutoff caused, hence the anode, grid current disappeared.
Repair, replacement note after the tube anode, cathode and gate leads to the copper belt have to maintain a certain distance. Filter capacitor in advance through a large resistance high voltage discharge to avoid electric shock. When replacing the AC contactor KM1 CJT1-20 substitution, but must have the rated coil voltage is 220V. After changing the grid resistance Rg, should adjust its resistance make the anode current vs grid current allowed range.