Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Raybob on December 27, 2010, 04:44:24 am

Title: Hoffman AB763 [47K resistor to ground?]
Post by: Raybob on December 27, 2010, 04:44:24 am

I'm building a Hoffman style AB763 board with brown vibroverb tremolo and see a resistor that I'm wondering why it's there.  This is the 47K resistor from preamp ground to the end of the .1 cap from pin 6 of v4 going to the 220K mixing resistor.  What exactly, is the purpose of the 47K resistor?

Raybob

Title: Re: Hoffman AB763 [47K resistor to ground?]
Post by: sluckey on December 27, 2010, 07:27:17 am

It replaces the missing 50K Intensity pot in the orig AB763 circuit.

Title: Re: Hoffman AB763 [47K resistor to ground?]
Post by: Fresh_Start on December 27, 2010, 10:13:05 am

That resistor (or Intensity pot in the stock AB763 circuit) reduces the signal level hitting the phase inverter.  Some guys have put it on a switch to go from stock to higher gain.  YMMV.

Chip