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04-13-2023, 01:53 PM
Hi Guys
As TUT3 (The Ultimate Tone vol.3) shows, bias pots should be actual panel pots NOT small trimmer pots. The reason for this is two-fold:
The life cycle of most trimmers is 200-cycles (rotations). Yes, you can find a few with higher ratings, but panel pots are still better. The least expensive panel pot that does not even provide a life-cycle rating is typically good for 15,000-cycles. You are not likely to approach this number even if you change tubes constantly.
The ergonimics of trimmers is exteremely poor. A tool is needed to manipulate most of the available styles; some have thumb screws on them. Bourns offers a chassis mount holder for some of their models, and this fits into the same hole-size as a 1/4" jack. You still need a tool to set the trimmer and there is still not as good life expectancy as a panel pot.
Per TUT3's recommendation, the bias pot should have the same accessibility as the tubes. In most cases, this means the pot should be externally accessible with the best mounting position being on the tube plane of the chassis. The pots and tubes then have the same protection and the same accessibility.
ideally, there are meter jacks on the rear apron of the amp for easy monitoring of the idle condition.
As TUT3 (The Ultimate Tone vol.3) shows, bias pots should be actual panel pots NOT small trimmer pots. The reason for this is two-fold:
The life cycle of most trimmers is 200-cycles (rotations). Yes, you can find a few with higher ratings, but panel pots are still better. The least expensive panel pot that does not even provide a life-cycle rating is typically good for 15,000-cycles. You are not likely to approach this number even if you change tubes constantly.
The ergonimics of trimmers is exteremely poor. A tool is needed to manipulate most of the available styles; some have thumb screws on them. Bourns offers a chassis mount holder for some of their models, and this fits into the same hole-size as a 1/4" jack. You still need a tool to set the trimmer and there is still not as good life expectancy as a panel pot.
Per TUT3's recommendation, the bias pot should have the same accessibility as the tubes. In most cases, this means the pot should be externally accessible with the best mounting position being on the tube plane of the chassis. The pots and tubes then have the same protection and the same accessibility.
ideally, there are meter jacks on the rear apron of the amp for easy monitoring of the idle condition.
