20w pep Power Amplifier

Refer to G6ALU web pages for full build information, please.

This page only shows the build of my own PCB. So far, everything fits OK.



Heatsink from junkbox has been selected, but not sure if it's big enough. It gets very hot so I will need to find soemthing with bigger fins.


The case I am using is an old test instrument, bought at a sale for $10. I stripped out all the interior (saving some of the "goodies") and made a new chassis for it. Plus a rear panel which I am mounting the PA onto. A large clearance hole in the rear panel allows the PA and heatsink to be removed from the rear of the radio. There are tapped bushes inserted into the rear panel, so no nuts are needed. You can see PnM also. There will be another panel fitted over the front, held in place by screws in the corners.


17th Dec 2007 I initially used a PN2222a as the first transistor. Some preliminary testing shows that the 2N2222a is NOT suitable. It rolls off very quicky at higher frequencies. I changed to a MPSH10 and got much better results but the 1.8MHz end is well down. Further investigation needed.

Testing was done at 2W output only, until I get a bigger heatsink.

Below is a graph (0-50MHz) of the response of my PA, with the MPSH10 fitted.

At 1.8MHz power output is ~7dB down. At 50MHz -8.5dB. The higher end may lift with a change to the emitter cap on the MPSH10, but this has not been measured yet.

From 7 to 30MHz, power output is essentially level.


December 18, 2007