RM HLA300 low power output.

[Stuuk]

R37 is part of the base bias / feedback circuit for one of the sd1446 RF power transistors.
It connects via a capacitor from the collector to the base then another resistor connects from the base to ground.
I've checked all the components around the transistors and they all seem to check ok.

 

[Robb]

But you haven't checked those transistors . . .

 

[Stuuk]

Solved

Ok looks like I found the problem with some help from Andrew at RM (nice chap)

At some stage someone has replaced one of the SD1446 transistors
This is obviously a different batch from the rest and has a different gain letter.
I didnt spot this but Andrew did from a picture

We're pretty sure this is causing the low power output due to the imbalance.

I guess the only real fix will be to replace all the SD1446's with a new matched quad set duuuuh

Not sure the amp is worth spending the money on as the SD1446's are very expensive in the UK.

Cheers

Stu