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What would be a typical value for the bias adjustment pot of a 845 amp?

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Posted on April 20, 2016 at 14:09:35
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 I found a defective bias pot on the 845 amp I am repairing. The pot is not your typical USA made one so I am unsure of its value. The total resistance of the pot that I measured is 17k which is an odd number. The printing on the pot has 33k and some logo or maybe Chinese characters? I am not familiar with 845 amps so I wanted to ask youse guys. cheers, Dak

 

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RE: What would be a typical value for the bias adjustment pot of a 845 amp?, posted on April 20, 2016 at 20:12:41
Chip647
Audiophile

Posts: 2649
Location: The South
Joined: December 24, 2012
 There is little current required to set tube bias, so the value of the pot is just so you don't overload the bias circuit. A 1K ohm pot will cause a -100 volt bias supply to dissipate 100mA which is way too much. A 10K pot with a 10K resistor to limit the ability to set zero bias voltage will present 20K which will draw 5mA This is probably a good level.

 

RE: What would be a typical value for the bias adjustment pot of a 845 amp?, posted on April 20, 2016 at 21:12:57
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 Hi Chip and thank you for the recommendation. I will see how that one works and let you know. regards, Dak

 

RE: What would be a typical value for the bias adjustment pot of a 845 amp?, posted on April 21, 2016 at 19:07:30
Tre'
Industry Professional

Posts: 17297
Location: So. Cal.
Joined: February 9, 2002
 You might want to measure the good one on the other amp.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

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