Carbsandcaps
Super Member
I’ve got this hearhkit aa-21 and it have some power problems. I’ll explain what each channel is doing:
Channel 1: 15vDc at the speaker terminals. I’ve replaced all the capacitors and out of spec resistors. All transistors test good. I replaced the outputs which were blown at some point during my testing. Yes they’re germanium. I’ve replaced the bias diodes with ma-20 transistors as per the interwebs. All my other vintages seem ok and I’m scratching my head. This side uses the phase inverter switch if that helps. When you inveet the phase the voltage goes to the common terminal.
Channel 2: I have low voltage to the driver transistor (see pictures the other channel is correct -15v the bad channel shows -9v). Voltage comes back up when I disconnect the ground after R27 (.15ohm) or remove x8L transistor. Again all the resistors, transistors and capacitors are within spec. I’ll write voltages I have on the schematic.
I have no audio output from the channel 2. I don’t want to hook up a speaker to channel 1 because of the 15v at the speaker terminals
Channel 1: 15vDc at the speaker terminals. I’ve replaced all the capacitors and out of spec resistors. All transistors test good. I replaced the outputs which were blown at some point during my testing. Yes they’re germanium. I’ve replaced the bias diodes with ma-20 transistors as per the interwebs. All my other vintages seem ok and I’m scratching my head. This side uses the phase inverter switch if that helps. When you inveet the phase the voltage goes to the common terminal.
Channel 2: I have low voltage to the driver transistor (see pictures the other channel is correct -15v the bad channel shows -9v). Voltage comes back up when I disconnect the ground after R27 (.15ohm) or remove x8L transistor. Again all the resistors, transistors and capacitors are within spec. I’ll write voltages I have on the schematic.
I have no audio output from the channel 2. I don’t want to hook up a speaker to channel 1 because of the 15v at the speaker terminals