Recently I acquired a Nokia ex-UMTS PA, one with two BLD6G22L-150BN dual LDMOSFETs. As with similar PA’s one FET is in class AB and the other is a Doherty in class C. Its bias circuit is in part similar to the circuit DB8SDQ describes in his article about the PA with two BLF8G22LS (which are single FETs). DL8SDQ describes in detail how to disable the Doherty and make that FET linear. In order to find out how to disable the Doherty circuit I explored the bias circuit on my board and discovered a pad next to a ground pad labeled PEAK and AB.
I suspected this could mean exactly what it said, and I tried via a successive series of resistors to ground that pad. With zero resistance to ground the gate voltage rose to 2.1 V, similar to the gate voltage on the linear side. At the same time the current increased from 1.5 to 2.5 amps for the whole PA. So grounding this pad effectively disabled the Doherty and made it work in class AB. As Bert, PA3AOD has a similar PA we had a look at his bias circuit. He has a PA with two BLD6G22L-150BN/2. Its bias circuit is different from mine, but it has also two (unlabeled) pads at the same place in the circuit. He tried shorting these pads with exactly the same effect. So if you have one of these PA’s, shorting these pads should be enough to disable the Doherty. Disabeling the Doherty improved linearity and increased output, especially at lower outputs, as was to be expected.