On my Wurlitzer 546 amp, I had a side of one of the power amps dead. I found one of the output power transistors was gone, and I read that you needed matched pairs. I ordered a matched pair from a seller on this forum. While waiting for the transistors I recapped the amp.
When I got the transistors put her all together tried and found the PA where I replaced the transistors was crackling. I discovered it was the new transistors. So I found another set ordered them, same thing. I did not know if I was overdriving the transistors or the speakers. I changed the 1.8 ohm resistor on the input of the 2 pa transistors to a 5 ohm resistor, noise was gone, a little lower output level but the heat sink for the transistors was just warm. Changed the five ohm to 2.7 still good and housing was still slightly warm. Question I have is it normal to have to change the base bias of the power transistors when you change the transistor. These are not Wurlitzer parts but a replacement part.
David