Hi, I was looking for some good wire wound resistor for my amp to be used on grid, plate, screen of KT88 tubes in my calss AB PP amp. I called this company.
http://www.precisionresistor.com/fi...r-SM-Series-Wire-Wound-Precision-Resistor.pdf
I spoke to one of their engineers who did not recommend wire wound resistors for audio application because he claims there is significant noise above 1 kHz. Are wire wounds really not appropriate for this application?
Thanks.
http://www.precisionresistor.com/fi...r-SM-Series-Wire-Wound-Precision-Resistor.pdf
I spoke to one of their engineers who did not recommend wire wound resistors for audio application because he claims there is significant noise above 1 kHz. Are wire wounds really not appropriate for this application?
Thanks.
Hi MGH
I think that's TOTAL trash.
What's the guy on about ?
Wire-wounds are well known to have WAY less noise than ANY other type of resistor.
As 'high value' anode loads etc. PERFECT !
Great for cathodes, as well.
The only thing to check is...
...Voltage Rating.
Some of the low-wattage ones...
...only have rating of 100v.
The popular 'Welwyn' green-ceramic wire-wounds, are like this...
3 Watt 100 Volts
7 Watt 200 Volts
10 Watt 500 Volts
14 Watt 750 Volts
Unfortunatly I don't see Welwyn producing typical high R load type values.
ERG is another brand to check ( US I think )
Also, most of the 'square cement' types available on eBay, are in my experience rated at 350 Volts ( check ! )
Some like this are available pretty cheap at high values like 100k 200k even 500k.
Aluminium-clad, are good as well, cheap on eBay.
Hope that helps.
Cheers.
Si.
PS... Morgan Jones, in his exellent book 'Valve Amplifiers' is BIG on using WW loads etc...
...there's a dude that KNOWS.
I think that's TOTAL trash.
What's the guy on about ?
Wire-wounds are well known to have WAY less noise than ANY other type of resistor.
As 'high value' anode loads etc. PERFECT !
Great for cathodes, as well.
The only thing to check is...
...Voltage Rating.
Some of the low-wattage ones...
...only have rating of 100v.
The popular 'Welwyn' green-ceramic wire-wounds, are like this...
3 Watt 100 Volts
7 Watt 200 Volts
10 Watt 500 Volts
14 Watt 750 Volts
Unfortunatly I don't see Welwyn producing typical high R load type values.
ERG is another brand to check ( US I think )
Also, most of the 'square cement' types available on eBay, are in my experience rated at 350 Volts ( check ! )
Some like this are available pretty cheap at high values like 100k 200k even 500k.
Aluminium-clad, are good as well, cheap on eBay.
Hope that helps.
Cheers.
Si.
PS... Morgan Jones, in his exellent book 'Valve Amplifiers' is BIG on using WW loads etc...
...there's a dude that KNOWS.
Thanks! That's what I thought. I asked the "engineer" if he knew anything about tube amplifiers and I was suspicious when he told me he knew enough, but didn't know what a plate resistor was.
How are noninductive WW resistors for grid and screen? I thought you have to have very low inductance or you could cause oscillations, so I am a little reluctant to use it. Some people seem to like carbon comps but heard they are not reliable.
How are noninductive WW resistors for grid and screen? I thought you have to have very low inductance or you could cause oscillations, so I am a little reluctant to use it. Some people seem to like carbon comps but heard they are not reliable.
Hi again MGH
Morgan Jones says inductance it so LOW it's not a problem...
...inductance seems to be one of the 'great audio myths' WW's are commonly stuck with !
Might affect an RF radio amp...
...Audio ?...
...Narr !
Morgan's THE man.
If you haven't got his book...GET IT !!!...NOW !!!
( I'm not his agent BTW...brilliant book...BRILLIANT )
0.5 deg phase-shift, worst case senario of inductance, @ 100Khz...no probs.
I just measured a load of UNUSED nos carbon-comps...
...ALL had drifted UP by as much as 30% !!!...
...some had gone COMPLETELY open-circuit.
Wouldn't go near 'em personaly.
These were brand new as well.
Stick a decent WW in...
...in 100 years time, it will STILL measure what it did today !
( now that aint bad )
If your doing a good job, don't skimp on the Watts rating ( not only for Voltage arc-over reasons ) Less heat, better dissipation...Less noise.
BINGO !
The golden age of wireless !
Cheers.
Si.
Morgan Jones says inductance it so LOW it's not a problem...
...inductance seems to be one of the 'great audio myths' WW's are commonly stuck with !
Might affect an RF radio amp...
...Audio ?...
...Narr !
Morgan's THE man.
If you haven't got his book...GET IT !!!...NOW !!!
( I'm not his agent BTW...brilliant book...BRILLIANT )
0.5 deg phase-shift, worst case senario of inductance, @ 100Khz...no probs.
I just measured a load of UNUSED nos carbon-comps...
...ALL had drifted UP by as much as 30% !!!...
...some had gone COMPLETELY open-circuit.
Wouldn't go near 'em personaly.
These were brand new as well.
Stick a decent WW in...
...in 100 years time, it will STILL measure what it did today !
( now that aint bad )
If your doing a good job, don't skimp on the Watts rating ( not only for Voltage arc-over reasons ) Less heat, better dissipation...Less noise.
BINGO !
The golden age of wireless !
Cheers.
Si.
Wirewound resistors with a low temperature coefficient--100 ppm or less are readily available and non-inductive windings. Mills, for example. They're inherently low noise and with low Tc, distortion is essentially non-measurable. Usually a nickel-chromium alloy, just like most metal film resistors and Vishay's foil resistors, which I think of as miniaturized wirewounds. I think they've been underappreciated.
Your main issue may be finding higher resistance values.
Your main issue may be finding higher resistance values.
Seriously off topic but...
Its a Peavey Patriot, had it about 15 years and it still plays like new.
See link below:
fleetwood mac the chain nigel playing along - YouTube
Some probably worthless generalizations-
Inductance of lower values is usually too low to worry about in the audio region.
Non-inductive winding patterns don't work as perfectly as one might like and can degrade things like self-capacitance.
Noise will usually be better than anything but metal foil ($$) parts.
Tempco will be better than any audio project needs.
Use caution if the WW is used for feedback around wide bandwidth parts like opamps. It may be audio, but you might be dealing with a 50 MHz GBW part that isn't aware of that!
The peak power handling ability of many WW resistors is extremely good- see Ohmite and Dale (Vishay) notes on this.
Given a roll of resistance wire, like manganin which is solderable, you can wind perfectly good WW resistors of any value you like and in any of the low inductance patterns you desire.
Inductance of lower values is usually too low to worry about in the audio region.
Non-inductive winding patterns don't work as perfectly as one might like and can degrade things like self-capacitance.
Noise will usually be better than anything but metal foil ($$) parts.
Tempco will be better than any audio project needs.
Use caution if the WW is used for feedback around wide bandwidth parts like opamps. It may be audio, but you might be dealing with a 50 MHz GBW part that isn't aware of that!
The peak power handling ability of many WW resistors is extremely good- see Ohmite and Dale (Vishay) notes on this.
Given a roll of resistance wire, like manganin which is solderable, you can wind perfectly good WW resistors of any value you like and in any of the low inductance patterns you desire.
A bit of inductance does little harm in audio, except in low impedance circuits, provided it is damped by some resistance too which is exactly what happens with a wirewound. Wirewound are usually the lowest noise resistors, because all you get is the unavoidable thermal noise. Other resistors have extra noise mechanisms too.
One proviso: it might be possible for wirewounds to introduce magnetic coupling between circuits so don't put them near each other and parallel unless a bit of coupling would do no harm.
One proviso: it might be possible for wirewounds to introduce magnetic coupling between circuits so don't put them near each other and parallel unless a bit of coupling would do no harm.
Hi Conrad.
SUPERSTAR !
Not worthless... GEMS !
Yep...I got some resistance-wire, & DIY hyper-matched source-resistors are in production...
...make your own resistors...
..." now that's DIY dude ! "
Flat-wound...& more acurrate than Vishay-foil...
...$$$$$$$$$$$$$$$$$$$$$$$ left over, to buy LP's with !
Hi DF96
Nice tip on the possibility of 'magnetic coupling'...
...hadn't thought of that one before.
Next board, designed with that in mind.
Thanks !
Cheers.
Si.
SUPERSTAR !
Not worthless... GEMS !
Yep...I got some resistance-wire, & DIY hyper-matched source-resistors are in production...
...make your own resistors...
..." now that's DIY dude ! "
Flat-wound...& more acurrate than Vishay-foil...
...$$$$$$$$$$$$$$$$$$$$$$$ left over, to buy LP's with !
Hi DF96
Nice tip on the possibility of 'magnetic coupling'...
...hadn't thought of that one before.
Next board, designed with that in mind.
Thanks !
Cheers.
Si.
Hi MGH
Is it the 'grid leak' resistor you mean ?
Anyway...
...these are always VERY high value.
It is possible to make this a wire-wound...
...I just scored a pair of 500k WW's on eBay ( 350volt, I think )...
There are lower voltage ratings out there as well.
But probably, you might want to use a 'High Stability' metal-film resistor.
This most likely has a 'spiral cut' anyhow, as well.
I don't think you're at all likely to get oscillations ANYWHERE using decent WW's.
Now trashey NOS carbon-compositions are another story...
...as said, I think before...
...we've measured 'brand new' NOS ones that are simply either WAY high (bad sign of stability), or just plain 'open circuit'.
I don't think you will have 'inductance problems' ANYWHERE with WW's...
...correct or 'over-rated' Voltage spec. is what's important...
...CHECK IT...not all WW's go to say 350v; I would prefer to see 500v or higher rating for a 350v PSU'ed amp.
The only real danger of inductance, I believe, is at very high frequencys, as said before...
...and very-low Ohm values, which aren't in most valve amps anyway.
Try it and see, is the best test.
You might be surprised to hear just how good WW's sound; especialy compared to rotten old carbon resistors.
Never need replacement either.
Well worth the extra 25cents !
Cheers.
Si.
Is it the 'grid leak' resistor you mean ?
Anyway...
...these are always VERY high value.
It is possible to make this a wire-wound...
...I just scored a pair of 500k WW's on eBay ( 350volt, I think )...
There are lower voltage ratings out there as well.
But probably, you might want to use a 'High Stability' metal-film resistor.
This most likely has a 'spiral cut' anyhow, as well.
I don't think you're at all likely to get oscillations ANYWHERE using decent WW's.
Now trashey NOS carbon-compositions are another story...
...as said, I think before...
...we've measured 'brand new' NOS ones that are simply either WAY high (bad sign of stability), or just plain 'open circuit'.
I don't think you will have 'inductance problems' ANYWHERE with WW's...
...correct or 'over-rated' Voltage spec. is what's important...
...CHECK IT...not all WW's go to say 350v; I would prefer to see 500v or higher rating for a 350v PSU'ed amp.
The only real danger of inductance, I believe, is at very high frequencys, as said before...
...and very-low Ohm values, which aren't in most valve amps anyway.
Try it and see, is the best test.
You might be surprised to hear just how good WW's sound; especialy compared to rotten old carbon resistors.
Never need replacement either.
Well worth the extra 25cents !
Cheers.
Si.
Thanks Space Egg. Please see the figure. I'm not sure what you mean by "grid leak" resistor, but I'm talking about 2.2 kOhm resistor (R6). I want to use noninductive WW resistor in this location.
In fact, I want to use noninductive WW for 100 Ohm screen resistor (R18) and 10 Ohm plate resistor (R12), as well.
Would you say noninductive WW are appropriate for all these locations provided the voltage and wattage requirements are met?
In fact, I want to use noninductive WW for 100 Ohm screen resistor (R18) and 10 Ohm plate resistor (R12), as well.
Would you say noninductive WW are appropriate for all these locations provided the voltage and wattage requirements are met?
Attachments
Hi MGH
Can you post a decent res. ( readable ! ) schematic of the WHOLE of the circuit you are interested in.
I don't think the 2.2k will have ANY 'worrying' inductance at all.
The smaller ones might...
...but again, perhaps ONLY an issue in a high-frequency RF amp.
I ain't the world's greatest 'expert' by a long-shot...
...but let's have a look at the whole schematic.
Be nice to see what you're making anyhow.
Cheers.
Si.
Also...where did the schematic come from ?
Is it a tested design ?
Is it a 'retro classic' etc. etc.
Can you post a decent res. ( readable ! ) schematic of the WHOLE of the circuit you are interested in.
I don't think the 2.2k will have ANY 'worrying' inductance at all.
The smaller ones might...
...but again, perhaps ONLY an issue in a high-frequency RF amp.
I ain't the world's greatest 'expert' by a long-shot...
...but let's have a look at the whole schematic.
Be nice to see what you're making anyhow.
Cheers.
Si.
Also...where did the schematic come from ?
Is it a tested design ?
Is it a 'retro classic' etc. etc.
I would post the whole schematic if I could, but it is a current production commercial amp. So I can't. These resistors are noninductively wound so I don't think there would be any issues at all, based on what you'r telling me.
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