Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jaster55 on December 30, 2016, 09:56:11 pm

Title: Erratic Voltage Readings
Post by: jaster55 on December 30, 2016, 09:56:11 pm

I just finished my Hoffman Princeton Reverb. Amp works fine and sounds amazing.
I took all the initial voltage readings comparing them to A Fender AA1164 layout from the Hoffman library.
All voltages are within 10% except V4 readings. Pins 1 and 3 are erratic pin 1 jumping all over between 150 and 350. I can not get a steady reading.
Pin 3 on V4 is doing the same... Reading between 1.8 and 3.0.
Pin 8 is the only steady reading that is not within 10%.  Should read 50 and it reads 60

I submitted my readings on the website

Does anyone know what would cause this???

Title: Re: Erratic Voltage Readings
Post by: sluckey on December 30, 2016, 10:31:53 pm

Pins 1,2,3 are the tremolo oscillator. They should be jumping around if the oscillator is working. Actually the voltages are smoothly changing at the tremolo speed but you would need an analog meter or scope to see that. A digital meter just makes it look jumpy because of the sample rate involved. Turn off tremolo with the footswitch and the voltages will quit jumping around.

Pin 8 is fine. Looks like you may be comparing voltage to the original Fender schematic. The note at the top of that schematic says the voltage readings are ±20%.