Apollo 645-062 owner manual Setting the Tube Bias

The triode/ultralinear switch allows the user to operate the Apollos in either of the two modes. In general, the sonic differences are subtle but for a given loudspeaker one mode is likely to sound better than the other. There is a complex relationship between the output transformer and the crossover network so try both and see which one works best in your system. This switch can be operated while the amplifier is playing but you will hear a small relay noise through the loudspeaker.

Standby Switch:

The Apollo amplifiers SHOULD NOT BE LEFT RUNNING WHEN NOT IN USE. Unlike solid state amplifiers, tube amplifiers should be shut down when not being used. This will greatly prolong tube life.

A standby switch has been provided for short-term use between listening sessions so that the amp will remain in a “warmed up “ state. I f you will not be listening to the amplifier for more than an hour, it is advised that the amplifier be turned off.

The standby switch lowers the voltage on the tubes and heater filaments to ½ of normal operating voltage. Some output (distorted) will be heard so the source material should be turned off when in standby mode.

SETTING THE TUBE BIAS

Tools required: bias tool (provided with amplifier)

The output tubes (the large ones) need to be “biased’ with a grid voltage that controls the flow of electrical current through the tube. Tube biasing on the Apollo monoblocks has been designed to be both simple and effective. On some amplifiers biasing is done for two or more tubes simultaneously. With this method, the total current flowing through the group of tubes may be correct, but the current flow through any individual tube may vary significantly from the optimal value. With the Apollo amplifiers the bias is set individually for each tube so that the correct operating point is assured. An added benefit to this approach is that, should a tube fail prematurely, the single tube can be replaced without having to purchase a matched set. Use the following procedure to set the tube bias:

WARNING – There are dangerous and potentially lethal voltages in side this amplifier. Do not touch any part of the amplifier other than as described below. If you are uncertain about any of these instructions, please contact your dealer and have them bias the amplifier for you.

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