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Ed_Dinning · 12th Sep 2019, 8:22 pm

Hi, if you have the circuit to hand, see if you can identify the feedback resistor from the op trans. replace with double the value for the 15R tap.
There may also be a cap involved in the circuit. This is often "tuned" by feeding a 1KHz square wave in and adjusting the cap for best waveshape on the output.

If you look at the details of the Mullard 5-10 amp it shows how the value changes with designed op impedance.

Ed

12th Sep 2019, 8:22 pm	#2
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Feedback Hi, if you have the circuit to hand, see if you can identify the feedback resistor from the op trans. replace with double the value for the 15R tap. There may also be a cap involved in the circuit. This is often "tuned" by feeding a 1KHz square wave in and adjusting the cap for best waveshape on the output. If you look at the details of the Mullard 5-10 amp it shows how the value changes with designed op impedance. Ed