Just had a call for a customer in the UK who wanted to know how to reduce the power of a 100W amplifier (same for a 100W transmitter) internally down to 70W to comply with OFCOMs licencing conditions. I said you can adjust the power internally, but there are some controls that you should never touch if you want to your amplifier to stay alive.

The picture attached to this post should help to clarify the purpose of each adjustment inside the amplifier.

Main Power Supply Power Adjustment
The main big 48V DC power supply is the best and recommended way to reduce the power. There is a little control at the front on the left hand side of it where all the cables connect. The power supply can be taken down to about 42V, this should reduce the power to about 70W with stability. If this is not enough, then DC Control board will need to be adjusted.

DC Control Board Power Adjustment
This control pot is marked FWD on the DC Control board. Only adjust this pot, DO NOT TOUCH THE OTHERS. This control is used to limit the amplifier to a maximum of 100W, it’s an AGC type control. With irresponsible adjustment this control can be adjusted so the amplifier does more than 100W, !!! DO NOT DO THIS !!!. It will work at more than a 100W for a while, maybe a day, maybe a week, maybe a month, but then it will die, so please don’t do it. You can adjust the power anywhere between about 10 and 100 watts with stability on this control. If you damage the amplifier through misuse of this control it will not be repaired under warranty

Other Controls Marked in Red
The other controls marked in RED should not be touched, these are factory set and are there for the sole purpose of protecting the amplifier against reflected power and over temperature. If they did not matter or were not needed, we would not have designed them and put them there, so please tread carefully. If you damage the amplifier through misuse of these controls it will not be repaired under warranty.

Paul Hollings