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help figuring out what has this guy done with the NFBL in an amp

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ELS122:
I've built a replica of an amp guitalogist made a few years ago:
but I can't figure out one thing, and it's the only thing he didn't really show, is the NFBL switch, it has 3 positions, on-off-on, he says that "it switches between 2 NFBL resistors, you can also put it in the middle where there's no NFB"
which would make me think he has a resistor to ground before the switch, because originally the amp got the DC bias on the PI trough the OPT.
here's the shematic of the output of his conversion of the amp that was last filmed (only thing he changed is coupling cap values from 47nF to 100nF)


the original amp was a Grommes-50PG2 (or PG3)

here's my best guess to what he has done with it,


maybe you have a better guess to what he did with the NFBL switch.

duak:
The 1K0 resistor has to do two functions.  The first is feedback from the transformer secondary.  The second is to establish the correct voltage on the cathodes of the 12AX7.  Your modified circuit will vary the DC operating point of the 12AX7 and cause some significant pops when switched.   It might be possible to split the 1k0 cathode resistor into say 900R in series with a 100R and applying feedback to the resistors' junction (in essence a 'T' network) but there would still be a variation in the DC operating point. 

To your modified schematic I would add a capacitor of at least 10 uF between the cathode of the 12AX7 and the feedback resistors.  The 2k2 resistor from the cathode to ground should be 1k0, the same as before.  There might be a small pop when switching feedback from charging or discharging the new capacitor so I would add a 10k resistor from the right side of the new capacitor to ground.

The new capacitor's value of 10 uF will give a gentle boost to frequencies below 20 to 30 Hz depending on the gain.  If you think this affects bass response, try increasing its value.

TimFox:
Assuming the DC connections to the cathode of the input triode are correct in your first drawing, then duak is correct in saying that the 1k resistor sets the bias point, since the cathode current flows through it.
My guess about a switch is that it switched the right end of the 1k resistor from the 4 ohm tap (less feedback), to ground (no feedback), to the 16 ohm tap (more feedback).  These positions would have the same DC voltage across the 1k.

ELS122:
well the guy said he doesn't recommend no NFB, at all, so I doubt he would intensionally put in a feature he would not want anyone using.
and the switch has 3 positions : on-off-on
so I'm guessing he had the cathode to ground with a 2.2k resistor, and switched between 2 NFBL resistor values from the 16 Ohm tap. cause that would make the most amount of sence

trobbins:
Are you using exactly the same output transformer?
Do you know the level of feedback, and if the amplifier is confirmed to be stable?

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