NFB resistor value

[acheld]

I'm planning to build a Hoffman 5F6A Bassman.   

The output transformer I have supports 2, 4 and 8 ohm speakers and I plan to use the 4 ohm line primarily, with a switch for using an 8 ohm speaker as an alternative.

The negative feedback resistor (R41) is listed as 27k.  I believe this is set based on an 8 ohm load.   Should I change the value of this resistor, say to 39k, because I am using the 4 ohm tap?

Somewhere, someone (I can't find the post) said to always use the 4 ohm tap as the source of NFB.  I'm not quite sure what that would mean.   My plan would be to use the active lead (at the speaker jack), regardless of which tap is being fed to the jack.  Is this the correct method of implementing NFB while using selectable speaker loads?

https://el34world.com/Hoffman/files/Hoffman_5F6A.pdf

[sluckey]

The original 5F6A had a 27K NFB resistor and used a 2Ω speaker load. So, I would use a 27K connected to the 2Ω tap just like Leo did. Then use whatever speaker load (2. 4, or 8) you choose. The tap you connect the NFB resistor to has nothing to do with the speaker load you choose.

[vampwizzard]

I'm planning to build a Hoffman 5F6A Bassman.   

The output transformer I have supports 2, 4 and 8 ohm speakers and I plan to use the 4 ohm line primarily, with a switch for using an 8 ohm speaker as an alternative.

The negative feedback resistor (R41) is listed as 27k.  I believe this is set based on an 8 ohm load.   Should I change the value of this resistor, say to 39k, because I am using the 4 ohm tap?

Somewhere, someone (I can't find the post) said to always use the 4 ohm tap as the source of NFB.  I'm not quite sure what that would mean.   My plan would be to use the active lead (at the speaker jack), regardless of which tap is being fed to the jack.  Is this the correct method of implementing NFB while using selectable speaker loads?

https://el34world.com/Hoffman/files/Hoffman_5F6A.pdf

Rob Robinette gives some values to look at for the 5f6a vs JTM45 at varying outputs https://robrobinette.com/5F6A_Modifications.htm#3-Way_Negative_Feedback_Switch

[acheld]

Many thanks.

I'm going to start with standard Bassman value off of the 2 ohm tap, but this information should make it easy to increase the NFB in the future (if desired) without changing the resistor.