Bias test resistors
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- StrummersOfThunder
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Bias test resistors
Regarding the 1ohm resistor from octal pin 8 to ground to facilitate easy calcualtion of bias current (1:1 mV/mA) in fixed adjustable negative bias set up.
Some call for 'current sensing' resistors ... where as lots of images just show regular metal oxide or metal foil 1% tolerance.
Also some say high wattage rating is needed but why would this be?
What resistors would the amp gurus favour here?
Can I safely just use plain jane metal foil 1/2-1 watt 1 ohm or do I ned to find something resembling a ochre coloured hot dog on the spit??
Thanks
Some call for 'current sensing' resistors ... where as lots of images just show regular metal oxide or metal foil 1% tolerance.
Also some say high wattage rating is needed but why would this be?
What resistors would the amp gurus favour here?
Can I safely just use plain jane metal foil 1/2-1 watt 1 ohm or do I ned to find something resembling a ochre coloured hot dog on the spit??
Thanks
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Re: Bias test resistors
In the mean time Ive just grabbed some 1% tolerance 2W metal film resistors.
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Re: Bias test resistors
'current sensing' resistors is just the term used for a resistor put in place so that you can measure the voltage across it, nothing special.
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- Jay
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Re: Bias test resistors
It will be fine in 'normal' temperature range. You can try to find the temperature coefficient of that resistor if you can find its spec. Even 1W is ample assuming the valve's max cathode current won't exceed, say 100mA.
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Re: Bias test resistors
These should be perfect.StrummersOfThunder wrote: ↑Sun Nov 03, 2024 6:59 am In the mean time Ive just grabbed some 1% tolerance 2W metal film resistors.
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Re: Bias test resistors
I love how stupid my questions look in retrospect.sizzlingbadger wrote: ↑Sun Nov 03, 2024 7:16 am 'current sensing' resistors is just the term used for a resistor put in place so that you can measure the voltage across it, nothing special.
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Re: Bias test resistors
You're providing a wonderful service for all of us who have no idea about this kind of thing!StrummersOfThunder wrote: ↑Sun Nov 03, 2024 7:58 amI love how stupid my questions look in retrospect.sizzlingbadger wrote: ↑Sun Nov 03, 2024 7:16 am 'current sensing' resistors is just the term used for a resistor put in place so that you can measure the voltage across it, nothing special.
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Re: Bias test resistors
The main concern is when the tubes fail and short out. Do you want resistors that will also burn out and need replacing or ones that will stand up to high current during failures? Some actually prefer to use low-wattage resistors here, to act like a rudimentary fuse but it’s probably a better idea to use 1W or more, unless you like replacing resistors every time you replace tubes.
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Re: Bias test resistors
I ask the questions SO YOU DON'T HAVE TO!jeremyb wrote: ↑Sun Nov 03, 2024 8:09 amYou're providing a wonderful service for all of us who have no idea about this kind of thing!StrummersOfThunder wrote: ↑Sun Nov 03, 2024 7:58 amI love how stupid my questions look in retrospect.sizzlingbadger wrote: ↑Sun Nov 03, 2024 7:16 am 'current sensing' resistors is just the term used for a resistor put in place so that you can measure the voltage across it, nothing special.
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Re: Bias test resistors
There are no wrong parts, you're just opening up opportunities for other future projects!StrummersOfThunder wrote: ↑Sun Nov 03, 2024 8:25 amI ask the questions SO YOU DON'T HAVE TO!jeremyb wrote: ↑Sun Nov 03, 2024 8:09 amYou're providing a wonderful service for all of us who have no idea about this kind of thing!StrummersOfThunder wrote: ↑Sun Nov 03, 2024 7:58 am
I love how stupid my questions look in retrospect.
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Re: Bias test resistors
jeremyb wrote: ↑Sun Nov 03, 2024 8:51 amThere are no wrong parts, you're just opening up opportunities for other future projects!StrummersOfThunder wrote: ↑Sun Nov 03, 2024 8:25 amI ask the questions SO YOU DON'T HAVE TO!
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