Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: xochipelli on March 25, 2024, 05:32:23 am

Title: Calculating variable NFB resistance on 5F1 champ with an 8 ohm OT.
Post by: xochipelli on March 25, 2024, 05:32:23 am

  I'm trying to wrap my head around a variable NFB on a fender 5F1 champ using a Mercury Magnetics 8 ohm OT.
  Now the Champ with a 4 ohm output uses a 22K NFB resistor so i'm guestimating that maybe  a 60ish K for an 8 ohm output?
Since this will be on a pot am i on the right track considering a 100K linear pot with a 10K resistor?
Ideally i would like the sweet spot located somewhere's near the 12 o'clock position on the NFB pot and not have the min/max positions to be unusable/sound like crap.
Any help would be appreciated - thx!

Title: Re: Calculating variable NFB resistance on 5F1 champ with an 8 ohm OT.
Post by: sluckey on March 25, 2024, 07:13:04 am

Just experiment. A 100K linear pot with a 10K resistor sounds like a good starting point. Set the pot to 12 o'clock and experiment with the 10K, changing its value up/down until you find your sweet spot.