Which one is the bias pot?

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Posts: 7
Joined: Tue Jun 26, 2012 12:00 am

Tue Aug 27, 2013 5:59 pm


unless i'm blind, i'm reading both as pr1, so if you know which one is the bias pot , please tell me if it's in the first pic, or the 2nd pic

This is a blackstar series one 100.

Posts: 77
Joined: Mon Jun 14, 2010 12:00 am
Location: NW England

Tue Aug 27, 2013 11:38 pm

Not familiar with the insides of the Series 1, but I'd go for the pot on the board that houses the output valves.

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Joined: Tue Jul 16, 2013 4:43 pm

Mon Sep 09, 2013 6:04 pm

For regulating de bias you have to use this pot

The other one is for regulating the hum.

Blackstar recommends a measure of 100mV (in a S1 104EL34) in the CON1, see http://i39.tinypic.com/2lm9pw6.jpg (Top left in the picture)


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Joined: Fri Oct 18, 2013 1:56 pm

Wed Oct 23, 2013 7:01 pm

K, here's the real deal on these PR1 pots. The pot closet to the pre-amp tubes is a balance adjustment between the pairs of EL34's. The pot located under or next to the cooling fins of the trans is the bias adjustment. If you have a bias probe you'll want to check a tube on the left & on the right to insure a balance between the pairs. My Series One 100 is running @ 452 plate volts so I assume yours will be in that neighborhood also. I've got mine biased @ 38 mV but I think I'll back it down a bit to extend tube life.
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