Quote:
Originally Posted by Kamakiri
In the above marked diagram, the cap that I believe I'm referring to is C3/C4? Showing a reading of .0033 uF on that schematic.
I took a reading off the second cap, taken out of circuit, and this is what I've got.
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Yes, C3 and C4, however in the circuit I sent you a copy of, they are connected to the centre tap of the transformer rather than to ground. This means they don't have to deal with B+ in addition to the signal voltage, so can have a lower voltage rating versus your amplifier, but the function is exactly the same.
This is an RC network, and exists to roll off the high frequencies (above the audible band) to prevent the amplifier from oscillating under certain circumstances, for example really long speaker wires. You could calculate the roll-off frequency using the source impedance of the output stage, and the RC values, similar to designing a speaker crossover network, however I really don't think the actual value is too critical - it's just got to be enough to stop the amplifier from oscillating. I also think it's unlikely you will install the amplifier in an auditorium with really long speaker wires as per original design, so chances are you could get away with deleting this network entirely and not even notice it's gone.