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Messenger 400


W9WDX Amateur Radio Club Member
Sep 24, 2010
Central Valley
forgive me first off, as I am sitting here in the er with my son with a broken wrist.

I have a Messenger 400 1x4 15m-80m amplifier. Love the amplifier but I would like to convert it from a low drive to a high drive, but lack the knowledge to do so.

The radio I am driving it with is an Icom IC-7000.

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Last edited:

I would leave the amplifier as it is and buy an amplifier that can take the input of your radio.
thank you Shockwave, i'll get that posted later on today.

as for leaving it alone, it isn't my style, I am all about making what you have work, you learn more, and enjoy the hobby more.

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There a few things going on here. The first is the 3 way power level switch. To bypass the driver correctly we should also be bypassing this resistive attenuator since the resistors will not handle any extra drive power.

The coax that goes all the way to the back relay board is the drive power coming from the radio through the relay. You'll want to remove that from the 3 way switch in the front of the amp.

I also see this amplifier uses tuned circuits between the driver and final stage and also on its output. I would like to keep the tuned circuit inline with the drive to these finals.

This reduces drive requirements by matching the impedance and prevents self oscillations since the circuit is tuned for the frequency in use.

I'm going to need a better picture of the silver coil near the driver output transformer. It looks like one side of this coil has an adjustable cap and the other side has a fixed cap.

I can't see what side of the coil has the coax attached and what side has the red wire from the output transformer. The side with the red wire on it will have this red wire removed from the output transformer and the coax you removed from the power switch will be soldered to this connection on the coil.

I'd probably remove the fixed cap that is on this coil to ground and replace it with the unused variable on the input side of the stock driver. Then you can adjust the input and output impedance of this tuned circuit.

Both caps should be adjusted for minimum input VSWR with the meter connected between the radio and the amp. The caps should bring it into range. If not, feel free to compress or expand the coil windings to improve the match.

I'd probably lift the 10 microhenry choke that feeds bias into the drivers input transformer. No sense dissipating the extra bias heat into the heatsink from this transistor.

This may be enough info for you to complete the mod. If not lets see a closer picture of that input coil and the connections to it. Then I can be more specific.

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