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Old 14th December 2012, 06:44 PM   #1
MGH is offline MGH  United States
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Default wire wound resistor

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/fil...n-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.
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Old 14th December 2012, 08:08 PM   #2
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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.
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Old 14th December 2012, 09:11 PM   #3
MGH is offline MGH  United States
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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.
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Old 14th December 2012, 10:12 PM   #4
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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.
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Old 15th December 2012, 12:10 AM   #5
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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.
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Old 15th December 2012, 12:25 AM   #6
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Quote:
Originally Posted by MGH View Post
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.
Wire-wound resistors have a little inductance that might affect an amplifier.

In practice I use them all the time with no problems.
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Old 15th December 2012, 12:33 AM   #7
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Wire-wounds ROCK !

Recently bought a pair of 500k WW's for an inverse RIAA...eBay.
Also just got 10 wire-wounds of 1,000,000 Ohms...NOS...eBay.
( WOW ! in series, a minimal-noise 10 MILLION Ohm resistor ! )

Is that a Strat Nige ?

Cheers.

Si.
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Old 15th December 2012, 12:35 AM   #8
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Under appreciated...m a y b e . . .
...certainly NOT under priced !
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Old 15th December 2012, 12:39 AM   #9
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Originally Posted by The Space Egg Corp View Post
Wire-wounds ROCK !
Is that a Strat Nige ?

Cheers.

Si.
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
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Old 15th December 2012, 04:35 PM   #10
MGH is offline MGH  United States
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May be someone can correct me. Is it the grid resistor than can induce oscillations if the inductance is too high?
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