[Elecraft] OT: modifying your amp for lower drive requirement

[AD6XY]

Luckily - most of the world is not the US and gains of over 15dB are legal
and common in non-us amplifiers. Modern FETs have much more gain than older
devices and it would be quite normal to have 20dB gain from a stage - even
after some feedback. There is an interesting design in the latest Dubus for
a 1kW 2m amplifier that requires only 5W input. That is tetrode territory. 

The popular THP 1.2KFX and 1.5KFX amplifiers use a 6dB input attenuator.
Bypassing this allows you to drive them with less power under 25W, though it
is not encouraged. The attenuator serves a couple of other purposes - it
prevents serious over-drive with a 100W rig and it improves the input match.

Incidentally - someone said with a 3dB pad the VSWR can't be more than 3:1 -
that is only true if the PA does not have a negative impedance or to put it
another way, return gain. That can happen when an amplifier takes off. 

Mike
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