Not wanting to run high power, I looked into getting a medium power amplifier. After reading many reviews on E-Ham, I decided to remain in the mid power range such as 400 to 600 watts. After checking into the Ameritron amplifiers on the market, I discovered that a friend of mine WA3TUN had one for sale at a fair price. I wanted this amp to be used with my Flex Radio 5000A but saw a warning on their site that the 5000A would not be covered under warranty if the darlington output transistors which supplied an amplifier keying circuit to ground failed. I talked to a ham on 40 meters who said I needed a buffer keying circuit such as made by Ameritron, the ARB-704. This unit was only $59 and soon had it wired from the Flex 5000A. It worked flawlessly keying the amplifier but something was missing, being able to work CW with faster amp switching time. Looking at Ameritrons web site, I found just what I needed, the QSK-5 which is a pin diode type switcher. I bought the circuit board unit being a little cheaper, $259 and installed it with the amplifier itself. Even though I am able to work QSK when barefoot with the 5000A, using two antennas, this QSK-5 is very fast indeed and follows my keying at 30 WPM with no problems. The Ameritron amplifier can work all day during a CW contest and remains cool since the switcher quickly disables the tubes conduction during key-up. My antenna requires tuning except for small segments within each band and with the Ameritron amplifier, I needed a tuner to handle the 400 watts or so. The Flex 5000A has a trim tuner built in which works fine when running barefoot but one advantage of using the Heathkit tuner is I can now tune the vertical to work on 160 meters and it does it well even though I can't figure out why. When using the tuned loop on 160 meters, I am able to then use the vertical for dual diversity reception even though it is not then tuned and transmit from the loop antenna. It gets somewhat complicated using two antennas but the Flex 5000A can manipulate the antennas in just about any fashion desired. Many contacts have been made on 160 meters where I could have not heard the station if using one antenna.
