Generally I re-order the same parts when I am running low (metal film 0.25W, "MR25"), but recently when looking to bulk buy through-hole resistors, I noticed lower wattage resistors are now available. Normally Beebs use 1/4W resistors in most cases but I see you can now get 1/6W or even 1/8W resistors. Can these be used in place of 1/4W, assuming they are the same tolerance?
Sometimes I can't get the correct values in metal film, in particular the 1M5 used in the Econet interface, and for a long time I have been using carbon film instead (CR25). Are metal film and carbon film interchangeable in the Beeb world?
What Watt Resistors for Beebs?
- BeebMaster
- Posts: 7431
- Joined: Sun Aug 02, 2009 5:59 pm
- Location: Lost in the BeebVault!
- Contact:
- 1024MAK
- Posts: 12806
- Joined: Mon Apr 18, 2011 5:46 pm
- Location: Looking forward to summer in Somerset, UK...
- Contact:
Re: What Watt Resistors for Beebs?
Can you replace a component with one having a lower power rating?
This should only be done if you know the actual amount of power that said component has to handle (and I mean it's worse case situation). Otherwise you risk the lower rated replacement component letting out the magic smoke.
Note also, that the physical size and type affect the voltage rating.
Having said that, for resistors running off a 5V supply, if the resistance is 220Ω or greater, then (assuming no external source of power can be present) it's not possible to overload a ⅛W (125mW) resistor.
Metal film resistors are considered to be superior to carbon film types. However, unless actually specified, most resistors in 1980s computers are carbon film types.
The advantages of metal film compared to carbon film:
Mark
This should only be done if you know the actual amount of power that said component has to handle (and I mean it's worse case situation). Otherwise you risk the lower rated replacement component letting out the magic smoke.
Note also, that the physical size and type affect the voltage rating.
Having said that, for resistors running off a 5V supply, if the resistance is 220Ω or greater, then (assuming no external source of power can be present) it's not possible to overload a ⅛W (125mW) resistor.
Metal film resistors are considered to be superior to carbon film types. However, unless actually specified, most resistors in 1980s computers are carbon film types.
The advantages of metal film compared to carbon film:
- Can withstand a higher temperature,
- Lower noise,
- Smaller size compared to carbon types for the same power rating,
- Better voltage coefficient and temperature coefficient,
- Long term stability,
- Tighter tolerances available.
Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki - for answers to many questions...
Fault finding index • Acorn BBC Model B minimal configuration • Logic Levels for 5V TTL Systems
BeebWiki - for answers to many questions...
Fault finding index • Acorn BBC Model B minimal configuration • Logic Levels for 5V TTL Systems
Re: What Watt Resistors for Beebs?
It's also worth noting that most 0.5W (or some manufacturers give you 0.6W) metal film resistors are physically the same size as the common (and older) 0.25W carbon parts.
Re: What Watt Resistors for Beebs?
https://www.aliexpress.com/item/1005002670881002.htmlBeebMaster wrote: ↑Thu Dec 28, 2023 1:43 pm Sometimes I can't get the correct values in metal film, in particular the 1M5 used in the Econet interface
- 1024MAK
- Posts: 12806
- Joined: Mon Apr 18, 2011 5:46 pm
- Location: Looking forward to summer in Somerset, UK...
- Contact:
Re: What Watt Resistors for Beebs?
1.5M 0.4W 1% https://www.rapidonline.com/1m5-1-0-4w- ... pe-62-3701
1.5M 0.4W 5% https://uk.farnell.com/vishay/sfr250000 ... dp/9476512
1.5M 0.25W 2% https://uk.farnell.com/multicomp-pro/mp ... dp/3650155
1.5M 0.25W 1% https://uk.farnell.com/koa-speer-electr ... dp/3541172
1.5M 0.6W 1% https://uk.farnell.com/vishay/mrs25000c ... dp/9465537
For example...
Mark
1.5M 0.4W 5% https://uk.farnell.com/vishay/sfr250000 ... dp/9476512
1.5M 0.25W 2% https://uk.farnell.com/multicomp-pro/mp ... dp/3650155
1.5M 0.25W 1% https://uk.farnell.com/koa-speer-electr ... dp/3541172
1.5M 0.6W 1% https://uk.farnell.com/vishay/mrs25000c ... dp/9465537
For example...
Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki - for answers to many questions...
Fault finding index • Acorn BBC Model B minimal configuration • Logic Levels for 5V TTL Systems
BeebWiki - for answers to many questions...
Fault finding index • Acorn BBC Model B minimal configuration • Logic Levels for 5V TTL Systems
- BeebMaster
- Posts: 7431
- Joined: Sun Aug 02, 2009 5:59 pm
- Location: Lost in the BeebVault!
- Contact:
Re: What Watt Resistors for Beebs?
Thanks for the replies, I should have replied sooner myself.
I was on the wrong tack to start with, I'd always assumed that the wattage of the resistors was how much power they consumed, not how much power could be safely put through them! So I had best stick to 0.25W I think, not that I am planning to buy any more, I already have about a trillion of them round here.
Might get some metal film 0.25W 1M5 though, now I know where to get them.
I was on the wrong tack to start with, I'd always assumed that the wattage of the resistors was how much power they consumed, not how much power could be safely put through them! So I had best stick to 0.25W I think, not that I am planning to buy any more, I already have about a trillion of them round here.
Might get some metal film 0.25W 1M5 though, now I know where to get them.