06-12-2018, 07:15 PM
As Jeffrey says, working out the value of two equal value resistors in parallel is easy - just divide by two.
Where the fun start is if the values aren't equal. The formula is then
1/Rt = 1/R1 + 1/R2 + 1/R3 etc.
However, normally you will only be concerned with two. If they are not the same value you will need to use that formula but it can be rewritten for two values as:
Rt = R1 × R2 / (R1 + R2)
which is much simpler. In practice, you will rarely need to use it. One case where you might is possibly to replace a critical high wattage cathode bias resistor when all you've got in a suitable rating is too high a value (but not much higher!)
You've got a lot of lower wattage rating resistors in various values, so the question is: What value resistor can you put in parallel with the one you've got to bring it down to the required value? Simple - take a rough guess and use the formula.
In this modern day and age you'd probably cheat and use an on-line calculator - of which there are many!
I've never encountered 'puffs' before, either. It is always 'puff' in the singular as a verbal version of pF (but you never, ever, write pFs, do you?)
'Uff' doesn't work in the same way but 'mike' is commonly used, as in 'a point one mike' - I don't think I need to explain why!
Where the fun start is if the values aren't equal. The formula is then
1/Rt = 1/R1 + 1/R2 + 1/R3 etc.
However, normally you will only be concerned with two. If they are not the same value you will need to use that formula but it can be rewritten for two values as:
Rt = R1 × R2 / (R1 + R2)
which is much simpler. In practice, you will rarely need to use it. One case where you might is possibly to replace a critical high wattage cathode bias resistor when all you've got in a suitable rating is too high a value (but not much higher!)
You've got a lot of lower wattage rating resistors in various values, so the question is: What value resistor can you put in parallel with the one you've got to bring it down to the required value? Simple - take a rough guess and use the formula.
In this modern day and age you'd probably cheat and use an on-line calculator - of which there are many!
I've never encountered 'puffs' before, either. It is always 'puff' in the singular as a verbal version of pF (but you never, ever, write pFs, do you?)
'Uff' doesn't work in the same way but 'mike' is commonly used, as in 'a point one mike' - I don't think I need to explain why!
