how to find the negative feedback resistor value for 8 ohm output

[pc1093]

Hi all,
the original negative feedback resistor is 15K for the 16ohm output.
My output is 8 ohm. I have tried 15K and it does not work. The transformer has Self-oscillation.

So what is the resistor value for 8 ohm?
thank you

[sluckey]

10.6K would give the same NFB from an 8Ω tap as a 15K from a 16Ω tap. However, there is no reason why a 15K will not work on your 8Ω tap. I suspect you need to swap the OT primary plate leads.