Repairing an Acoustic Control model 120 bass amp head

[phatt]

Most poweramp designs use the differential input system which is just a high current opamp so any info you find on operational amplifiers is going to help in understanding how it works.

This might help get you started;
https://en.wikipedia.org/wiki/Direct_coupling

If you track down an internal schematic of the classic uA741 chip you will soon come to see the circuit of your amplifier is based on the same basic principal.

Read more here;
https://en.wikipedia.org/wiki/Operational_amplifier
Schematic of a uA741 is halfway down the page.

But to help simplify the idea down to a basic structure, look at this drawing;
http://ecircuitcenter.com/Circuits_Audio_Amp/Basic_Amplifier/Basic_Audio_Amplifier.htm

Phil.

[gbono]

I have used the 2N3440 (NPN) and the 2N4033 (PNP) to replace those RCA type numbers. You can get these parts from Digikey for $2 or less (not including shipping) - I believe Central Semiconductor is the last source for these metal can transistors. You press out the bad transistor from the heat sink (note the orientation of the tab on the can and the heatsink) - press in the new part - some fitting may be needed.