[Amps] SB 220 with 3 400 tubes

[Colin Lamb]

It has been noted that the 3-400 has a lower plate dissipation than the 3-500.  

However, it is not quite that simple.  The dissipation is controlled by the air blowing by, and both the power supply and the air will limit the power dissipation of the amplifier.  

The power dissipated by each tube is roughly the input power, less the output power, divided by two.  The amount of heat withdrawn from the amp is controlled by airflow and will be roughly the same for each tube.  My experience with both the Drake and Heat series is that they like to run at about 1200 - 1300 watts output, and will do so for a long time.

So long as the 3-400 tube is operating within limits, it will work the same as the 3-500 tube.

73,  Colin  K7FM