18-06-2025, 04:33 PM
(This post was last modified: 18-06-2025, 04:35 PM by ppppenguin.)
Skeleton preset potentiometer aka variable resistor. Nasty little things. If it's setting the output bias, depending on how it's wired, it's a good way to destroy the output transistors. The examples I've sketched may not be exactly as in your set but they are typical.
In the very bad example, even a slight intermittent contact will kill the output transistors. In the better example at least it can't go open circuit but a bad contact can still cause way too much bias. Best way is to have a fixed resistor doing most of the job and the pot just trimming the bias.
It would be useful to know the make and model. Ideally a circuit (schematic) diagram, but we may be able to find that if we know the type of set.
In the very bad example, even a slight intermittent contact will kill the output transistors. In the better example at least it can't go open circuit but a bad contact can still cause way too much bias. Best way is to have a fixed resistor doing most of the job and the pot just trimming the bias.
It would be useful to know the make and model. Ideally a circuit (schematic) diagram, but we may be able to find that if we know the type of set.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
