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A public thank you to Jerrold Tiers

Discussion in 'Amps [BG]' started by orangechicken, Jan 8, 2013.

  1. orangechicken


    Dec 21, 2012
    Likes Received:
    This started as a PM to him, but hopefully it can encourage others.

    I had low-volume distortion coming from an Ampeg SVT-III Pro and searching the web lead me to believe it might be a bias issue (this amp had been carted around sometimes not-so gently which might've given the bias pot "drift").

    I found several posts by Jerrold Tiers with the info on rebiasing with just a meter (and a steady hand and a plastic potentiometer adjuster).

    After reading everyone else (and even him in several posts) saying to leave it to a tech to do, I decided to ignore that (due to a time crunch) and stick with "common" sense and his instructions: average of 25mV across each of the two banks of resistors with none going over 1.5x that.

    At first I was nervous when my first checks with my multimeter showed 0mV across the resistors. I verified my meter was working correctly and began to ever-so-slightly nudge the pot up, checking voltages each tiny movement.

    I eventually got to an average of 18mV and my next movement put a couple into the 40mVs so I clicked it back down to 18mV. Took a deep breath and plugged it back into the cab.

    The result: A buttery tone with no more distortion! :bassist:

    I'm a very happy camper now, but I don't want ignorance to bite me: Is there anything wrong with me leaving it at 18mV average? The amp sounds good (and the fan speed is normal so I don't expect any heat issues).

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