70 MHz modification of a MML144/100

By Costas SV1DH

Details of MML144/100 successful modification to 4m on a very stable manner.

For just 6W in, I can get 100 W RF out (measured by HP power meter) at 13.8 V and at about 13 A.

Please note that my MML144/100 is of the OLD design and the stripline and component layout is maybe quite different from yours.

For the input circuit I added two extra 60 pF trimmers, one in place of the series fixed 470 pF DC block ceramic capacitor and another to ground, just after the previous one. Also at the transistor base I added two 180 pF silver mica capacitors.

For the output circuit I had to cut the stripline and to add one turn coil JUST AFTER transistor collector and after this coil to add two 100 pF SMD and an air variable cap of 40 pF, all to ground. To suppress second and third harmonics down to approx -50 dB, I used two series resonance LCs using the two small air capacitors of the 144MHz output circuit design. The use of silver mica, chocolate looking, mil capacitors was essential, since all other "mica" types were getting VERY hot (and lossy...) at the output  circuit...  I think the important component placement is for the mica caps JUST NEXT to transistor base (to ground) and the tuning air and mica caps (good quality, otherwise are overheated) JUST AFTER the 1 turn collector coil.

If during tuning with 6-7 W input, the total current is less then ~8-9A then maybe NO GOOD input matching, so try the 60 pF trimmer in series with your stripline, cutting it close after the relay. If input tuning is OK and current ~10-11A but no output more then ~50W, then you need better output matching and try modifications on the output circuit, especially as my comments before.

Close up of the matching circuit.