160 Watt Mosfet Amplifier for Four Metres
The pictures below show the finished amplifier. The internal picture shows the main body of the unit which has been running well for some years now so I decided it was about time I finished it off by fitting it into a suitable case with the required switching and built in power/swr meter.
R1 47k C1 200pf L1 12micro H, 4T 22swg on ferr ring
R2 6k8 C2 4700mfd
R3 33k C3 4700mfd L2 62nH, 4T 18swg 8mm dia
R4 10k C40 0.01mfd
R5 8k2 C5 1mfd L3 24nH, 1T 18swg 8mm dia
R6 5k multi turn C6 1mfd
R7 2k7 C7 1mfd L4 650nH, 9T 20swg 8mm dia
R8 10k themistor C8 0.01mfd
R9 22k min pot C9 0.01mfd L5 67nH, 4T 18swg 8mm dia
R10 470r C10 0.001mfd
R11 33r C11 0.001mfd L6 150nH, 6T 18swg 8mm dia
R12 470r C12 0.01mfd
R13 220r C13 0.05mfd L7 170nH, 7T 18swg 8mm dia
R14 220r C14 0.001mfd
R15 10k C15 470pf L8 450nH, 6T 18swg 8mm dia
C16 65pf min trim
C17 65pf min trim
C18 65pf min trim TR1 BC108 etc
C19 47pf 9kv(see text) TR2 BC108 etc
C20 47pf TR3 BC301 etc
C21 30pf comp trim TR4 SD2931 or equiv
C23 82pf F1 12v fan
C24 47pf RL1 12v min relay
IC1 LM7805 reg ic
NB, C19 should be a high quality compression trimmer which I found difficult to obtain so I decided to fit a lower quality trimmer here keeping the power down BELOW 50watts to find the approximate capacitor value which turned out to be 47pf. The trimmer was thus removed and replaced with a fixed capacitor of 8kv wkg and final tuning can be made by closing or opening the turns on L5, this has proved to be very reliable as any arcing at this point using a trimmer which is not up to the job will quickly see off the mosfet, you have been warned!
The thermistor R8 should be fitted directly above the mosfet with some heat sink compound and with careful adjustment of R6/R9 it is possible track the temperature change in the device keeping the standing current at about 250mA.
The input and output changeover relays, switching and meter circuits have been omitted here as these will depend on your own requirements. For FM operation the bias is removed completely, linear operation is of course not required which greatly reduces the heating of the device. The cooling fan starts up the moment the transmitter is keyed and continues to run for about one minute after returning to receive mode to aid cooling.
Even with the mosfet supply reduced from 50 to 30volts almost 100watts output is possible.