Increase resistors wattages by combining them ...any reason why not to? (tube amps)

[Poppy]

Hi,


some resistors in tube amplifiers need to be able to handle some higher wattages, as you know. Is there any reason, why I shouldn't combine resistors to increase their max. power values? Or doesn't this create any difference or dangers and I don't have to buy the whole range of high power resistors of any value to be able to experiment at home without waiting for ordered parts all the time?


Thank you!


poppy

 

[myleftear]

As far as i know, you‘re good with it, except that you‘ll be using more parts, more space and a good calculator...
Diyaudiostore‘s universal PSU works this way and is recommended for Nelson‘s treasures, so:

 

[ubergeeknz]

Just beware that putting resistors in parallel will of course increase overall power dissipation capacity, but won't increase voltage isolation capability. However, resistors in series will achieve both.

 

[jan.didden]

Hi,


some resistors in tube amplifiers need to be able to handle some higher wattages, as you know. Is there any reason, why I shouldn't combine resistors to increase their max. power values? Or doesn't this create any difference or dangers and I don't have to buy the whole range of high power resistors of any value to be able to experiment at home without waiting for ordered parts all the time?


Thank you!


poppy

Do you know how to calculate the equivalent resistance from putting two or more in series or parallel? And how to calculate the equivalent power handling when the resistors are not equal?

Jan

 

[JonSnell Electronic]

Early solid state Television power supplies used a 270R 1W resistor from the 340volt HT to start the power supply oscillator. They used to use a 150k and 120k in series. Both rated at 1/2W and the higher valued resistor used to fail first because the inadequate wattage of the 150k resistor.
Be careful when deciding specific values.
Resistors in parallel just add the power ratings but resistors in series be cautious. The higher value resistor dissipates more power than the lower value. (Kirchoffs law) Isaac Physics

 

[ubergeeknz]

Early solid state Television power supplies used a 270R 1W resistor from the 340volt HT to start the power supply oscillator. They used to use a 150k and 120k in series. Both rated at 1/2W and the higher valued resistor used to fail first because the inadequate wattage of the 150k resistor.
Be careful when deciding specific values.
Resistors in parallel just add the power ratings but resistors in series be cautious. The higher value resistor dissipates more power than the lower value. (Kirchoffs law) Isaac Physics

Resistors in parallel just add the power ratings but resistors in series be cautious. The higher value resistor dissipates more power than the lower value. (Kirchoffs law) Isaac Physics

In parallel, they also won't dissipate evenly unless they're the same value. The smaller value in this case will dissipate more as it will carry more of the current.

 

[Mclaren2]

I don't like to put resistors in parallel to achieve a higher wattage dissapation.
If one should fail, the wattage dissapation of the other could increase dangerously.

 

[davidsrsb]

Series is better as modern resistors have limited maximum voltage. Derate the power a little as most resistors rating assumes a lot of heat goes down the leads.

 

[Speedskater]

Only a few resistance values have both a maximum voltage and a maximum power limit. For all other values, one of the limits will be reached before the other.

 

[ubergeeknz]

I don't like to put resistors in parallel to achieve a higher wattage dissapation.

If one should fail, the wattage dissapation of the other could increase dangerously.

Hm, that shouldn't be true in most applications. The voltage drop across the remaining resistor may increase, if there is a load in series, but in that situation, the current flow will also decrease.

 

[Ben Mah]

Provide a factor of safety of 2 or 3 (derate the power capacity) to lower the chances of failure. That will also keep the resistor temperature to a reasonable level.