Electronics > Beginners
Trimpot rating when in place of two resistors??
Robbie010:
Hi All,
I have a schematic for my amplifier circuit board that shows two resistors on either side of an NPN transistor, 1 750ohm .25w and one 4750ohm .15w. However, on the actual circuit the resistors have substituted for a 10kohm trimpot for bias adjustment. I have been advised to replace the old carbon trimpot for a modern cermet one for good measure.
However, as the original resistors were rated at .25w each, do I need a .5w trimpot or .25w?
Thanks.
Brumby:
It's going to depend on the voltage across the pot.
Can you show us the schematic - and point out the relevant location?
Robbie010:
--- Quote from: Brumby on February 12, 2019, 12:54:26 pm ---It's going to depend on the voltage across the pot.
Can you show us the schematic - and point out the relevant location?
--- End quote ---
See attached.
The trimpot is used in place of R11 & R12 to the base of Q6, both resistors are .25w.
alex.martinez:
--- Quote from: Robbie010 on February 12, 2019, 01:03:01 pm ---
--- Quote from: Brumby on February 12, 2019, 12:54:26 pm ---It's going to depend on the voltage across the pot.
Can you show us the schematic - and point out the relevant location?
--- End quote ---
See attached.
The trimpot is used in place of R11 & R12 to the base of Q6, both resistors are .25w.
--- End quote ---
You should be good with a 1/4 W resistor. It's for bias, so don't expect a huge current through it.
Ian.M:
R11+R12 should *NOT* be replaced by a trimpot as that prevents the bias limiting safety circuit (D3, R13) working properly if you turn the trimpot too far.
Instead R11 should be replaced by the trimpot, wired as a variable resistor, keeping R12 as specified on the schematic.
Provided you refit R12, the trimpot's dissipation will be negligible as there should never be more than 4V across the Vbe multiplier.
Navigation
[0] Message Index
[#] Next page
Go to full version