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05-03-2023, 11:52 AM
Hi Guys
When selecting power resistors, look at the dimensions for the prospective devices, assuming you are doing a search at Mouser or Digikey.
Note that both suppliers offer free shipping for orders over C$100.
When using their search engines, first select the type of part you are looking for: 'passive', then select 'resistors' or 'through-hole resistors', then select 'in stock'. Sometimes the system will not highlight the 'apply' button unless two parameters are chosen, but it is best to select only one parameter at a time for filtering. Trying to narrow the search too quickly often leads to 'no parts found'
Another detail regarding resistors is that they have voltage ratings.
Most 1W metal-oxide resistors are rated for 350V yet they generally work without issue in typical tube amps with 500V supplies. It is better to select the larger body (approx. 15mm x 4mm) instead of the smaller, newer ones (7mm x 3mm) as the larger has a higher voltage rating. In positions where the voltage across the resistor will be low even if both ends are at high-voltage, you can get away with the smaller body provided the device is elevated.
In other places, I have written about thermal management for diodes, zeners and transistors inasmuch as all devices rely on their leads for their main heat transfer path. Therefore, it is advisable to retain as much lead length as is reasonable for the application.
When selecting power resistors, look at the dimensions for the prospective devices, assuming you are doing a search at Mouser or Digikey.
Note that both suppliers offer free shipping for orders over C$100.
When using their search engines, first select the type of part you are looking for: 'passive', then select 'resistors' or 'through-hole resistors', then select 'in stock'. Sometimes the system will not highlight the 'apply' button unless two parameters are chosen, but it is best to select only one parameter at a time for filtering. Trying to narrow the search too quickly often leads to 'no parts found'
Another detail regarding resistors is that they have voltage ratings.
Most 1W metal-oxide resistors are rated for 350V yet they generally work without issue in typical tube amps with 500V supplies. It is better to select the larger body (approx. 15mm x 4mm) instead of the smaller, newer ones (7mm x 3mm) as the larger has a higher voltage rating. In positions where the voltage across the resistor will be low even if both ends are at high-voltage, you can get away with the smaller body provided the device is elevated.
In other places, I have written about thermal management for diodes, zeners and transistors inasmuch as all devices rely on their leads for their main heat transfer path. Therefore, it is advisable to retain as much lead length as is reasonable for the application.
