An amplifier or an amp help makes the power of a signal increase. This makes recorded music as well as musical instruments like guitar sound louder. Tubes are usually used in amplifiers. These will eventually wear out so you need to replace these with new ones. These also need to be biased to have the best output. Biasing the tubes needs to be done properly to prevent these from burning fast. If this happens, you will need to change tubes again in just a short time wasting money and time. Bias is a DC voltage, which is applied to the same point of circuit like AC audio signal. The main goal in biasing the tubes is to balance standby current and crossover distortion. The left and right power tube amplifier must be changed and biased if damaged.
Here are the steps on how to bias for right power tube of amplifier.
- Remove the damaged tube and replace with new ones. Remove the amplifier from being plugged. If you just used it, let this cool down first. Tubes can be very hot so you need to be cautious to avoid hurting yourself. Remove the back cover of the amplifier to access the tubes that are secured by screws. Use a screwdriver to remove the screws and remove the back panel. Remove the damaged tube and replace these with new ones. The tubes need to be the same type. Make sure to place the new tubes carefully on the socket. To do this, firmly push the tubes to fit in the socket. If these are not placed carefully, the amplifier will not work properly. Pre-amp tubes can be replaced individually while power tubes need to be replaced in pair.
- Connect the voltmeter. There are 3 pin connectors that you will use in setting the bias. These are usually accessible by removing the cover at the back of the chassis. If you can’t find the pin connectors, refer to your amplifier manual to see where to find the 3 pin connectors for setting the bias. You will need insulated alligator clips to connect the voltmeter to the pin connectors. The center pin on the 3 connectors is for the ground. Connect the negative lid from the voltmeter to the center pin then connect the positive lid to the right pin. The voltmeter should be set to millivolts. Plug in the amplifier, turn it on and turn standby off. Let the amplifier warm up to start testing the bias.
- Set bias for right power tube of amplifier. The lid connected to the ground or middle pin will be the resistor. The voltage that you will get in measuring this with your voltmeter will be similar to your amplifier’s current while on standby. The voltage should be the same on the lid connected to the right pin. If the measurement that you get on the right pin is not the same, adjust this using the adjustment pot to get the same voltage.
When you get the same measurement on your volt meter, this means that the right power tube on the amplifier is properly biased.