600w Mosfet Linear Rf Amplifier Using APT5020BN

By :  Ir.Eliza Sukiman.MM.MA 

This is my base station of MosFet Linear Rf Amplifier  The MosFets are APT5020BN ,I have used them in my base station and they produce a good 600w from 36V on 160 and 80,and 400w on 7 Mhz. , I've had 600w out of four at 36V on 160 with a one turn primary / four secondary on the output transformer. (Tubing Transformer).
The circuit  is two devices with combiner on each side of the push-pull. The golden rule is to use a fet capable of withstanding three times your maximum supply voltage.

The Rf Power Amplfier as shown needs 25W of drive for full output. The input transformer T1 is wound on a small tubing transformer with about Three turns pri. and one turn sec., but a ferrite ring would do equally well. The 10 Ohm gate load resistors are 20 Watt power resistors and the attenuator resistors are 2 Watt metal film. The thermal sensor contact with the heatsink and well decoupled to prevent RF pickup.

The output transformer uses two large anti-EMC clip-on two part ferrite tubes . The primary is one turn of tubing transformer and the secondary is 3 turns of thinner multistrand stuff .
The choke (RFC)feeding the output transformer (optional, some seem to work OK without it) is wound with 1.5mm enam. copper wire on toroid . I have also fitted a fuse in the line at this point, a 20A automotive blade type is suitable. The Band pass filters are wound with 1.20mm enam. copper on pieces of 20mm O.D. plastic pipe. Turns and capacitor values as follows.

The power supply for this Rf Power Amplifier doesn't need regulating but shouldn't sag to less that 36 Volts at full load (about 30 Amps). I used a 35 Volt transformer with a 30 Amp bridge rectifier and Four large 10,000uF capacitors. The standing current should be set to about 200 ma by adjusting the 10k Ohm pot carefully! Remember these FETs can really draw some current!

I have done some experiments with a four device version. Firstly I tried APT 1010s which worked fine on 160 at 24V, producing 500W. They weren't so keen on 80 though and 40 was no good at all! I replaced them with APT 5020BNs (as in the 500W version) and it seemed altogether more enthusiastic. I can still get 600W on 160, about the same on 80 and 400 on 40. For the output transformer I am using a single-turn copper tube primary (through two large EMC ferrite tubes) with a five-turn secondary. I think I will probably stick with the one-turn primary in future, it works better on the higher bands.
Any more good ideas? Let me know and I'll try them and/or publish them here

Let see  . . . schematic

New power-MosFets coming out every week or so, look for ones with a low Rds-on and high power dissipation. The main drawback is the high gate capacitance, several thousand pF, which makes them hard to drive above 7MHz. Check out IRF , IXYS and APT ( FET manufacturers)

See Youtube 300w ...  Click Here

See Youtube  600w ...  Click Here

See Youtube 800w ...  Click Here


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