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I thought I would double check, and found that the amp only draws big current when its turned on at the front panel. I can connect it to 12 volts without it being switched on and it does not draw the big current. Does this indicate anything ?

Thank you - I think I have located where the damaged track went on the power selection board. I used a strong mag glass and there is a very fine mark where the track was, so I have repaired that. The next will be your procedure for testing the bias circuit. The output transistors in this amp...

I used a solder sucker and removed all four from the PCB and tested them out of the amp one at a time and the tester said they were ok. I may remove and test them again to make very sure.

Thanks for the comments. Yes the heat sink starts to get hot the moment its connected to 12 volts even with the front power switch turned OFF. But it dose not blow the 35A power fuse. I checked the 4 x output transistors Motorola MRF455 which show ok. The tester checks for, O/C Junction: S/C...

Hi all, I have been given a Palomar TX5500 RF amplifier which has a fault. When 12 volts is applied it draws heaps of current. I have checked the 4 x MRF455 output transistors and the tester indicates that they are ok. The previous owner said it was working fine between 10m-30m and he...