RM BLA350 Linear HF amplifier
Oh we know how to have fun in the play-pen. Seen a couple of these and they are nicely made, by our Italian friends, pieces of equipment. Components are good and the build is such that should the owner decide to blow seven shades of you know what out of them, repairs are not too nightmare generating.
This amp had been in before after going up in a cloud of smoke whilst an external aerial tuning unit with a personality disorder was being used. One of the two SD2941-10 output MOSFETs had blown apart. The other tested okay. But, to be sure, both were replaced. And, yes, expensive at 120€ a shot. The amplifier tested fine.
After a few hours’ use and again following switching bands, there was a reported pop and a cloud of smoke. One of the SD transistors was dead, but the other was reading okay. So, let’s make one good pair, using the recovered working transistor from the original fault.
The manufacturers RM are very helpful and provided all the set-up information. In a hidden menu, you can power the output stage to set up bias for both transistors independently. It was found that one of the multiturn trimer potentiometers seemed to have a loose screw control and when knocked, the bias changed. May have been the cause of the failures from the start.
Nice amplifiers covering the various amateur bands, auto selecting and good protection features.