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Sprague KoolOhm

W

Winfield Hill

Jan 1, 1970
0
Does anybody know what became of the Sprague
KoolOhm non-inductive power-resistor line -- who
owns it now, what did it evolve into?

I don't think Vishay got the line, since apparently
Ohmite owns the tradmark. Did they discontinue
them? What happened?
 
W

Winfield

Jan 1, 1970
0
Re: Sprague KoolOhm, low-inductance jelly-bean power resistors from a
bygone era

Does anybody know what became of the Sprague
KoolOhm non-inductive power-resistor line -- who
owns it now, what did it evolve into?

I don't think Vishay got the line, since apparently
Ohmite owns the tradmark. Did they discontinue
them? What happened?

Nobody has responded to my post, so I'm emphasizing:
Sprague's famous Koolohm molded power resistors were
popular for decades, and were famed for performance
other resistors couldn't equal.

I've been measuring the self-inductance of all kinds
of wire-wound power resistors. Series inductance is
the parameter that limits the usefulness of modern
wire-wound resistors in many applications, from high-
current pulsing to H-bridge monitoring to RF to
vacuum-tube transmitter stages (oops)...

So far I've failed to find parts to equal these old
beauties, within a factor of 10 or more in most cases,
and so I wonder what's become of them. I'm asking
what we're all supposed to be using now. Consider:
the appealing thing about them was they were standard,
readily available parts, not special-order Aryton-Perry
windings with a high price and 1k minimum orders, etc.

I've got a few answers, but I really want to hear from
ya'll out there first. Somebody knows what went down,
and I'm eager to hear about it.
 
J

John Larkin

Jan 1, 1970
0
Re: Sprague KoolOhm, low-inductance jelly-bean power resistors from a
bygone era



Nobody has responded to my post, so I'm emphasizing:
Sprague's famous Koolohm molded power resistors were
popular for decades, and were famed for performance
other resistors couldn't equal.

I've been measuring the self-inductance of all kinds
of wire-wound power resistors. Series inductance is
the parameter that limits the usefulness of modern
wire-wound resistors in many applications, from high-
current pulsing to H-bridge monitoring to RF to
vacuum-tube transmitter stages (oops)...

So far I've failed to find parts to equal these old
beauties, within a factor of 10 or more in most cases,
and so I wonder what's become of them. I'm asking
what we're all supposed to be using now. Consider:
the appealing thing about them was they were standard,
readily available parts, not special-order Aryton-Perry
windings with a high price and 1k minimum orders, etc.

I've got a few answers, but I really want to hear from
ya'll out there first. Somebody knows what went down,
and I'm eager to hear about it.

They're not in the same power league, but Caddock makes some
thick-film power resistors that are flat up into the 5+ GHz range. The
smaller ones, like 950 ohms stuck in an SMA female, make nice 8 GHz
scope probes.

The MS series goes up to 22 watts.

John
 
W

Winfield

Jan 1, 1970
0
They're not in the same power league, but Caddock makes some
thick-film power resistors that are flat up into the 5+ GHz
range. The smaller ones, like 950 ohms stuck in an SMA female,
make nice 8 GHz scope probes.

Nice trick.
The MS series goes up to 22 watts.

Thanks, John! Yes I know about some modern candidates
resistors that are either low power, or rather expensive.
I'm wondering about modern low-inductance Jellybean parts.
 
L

legg

Jan 1, 1970
0
Does anybody know what became of the Sprague
KoolOhm non-inductive power-resistor line -- who
owns it now, what did it evolve into?

I don't think Vishay got the line, since apparently
Ohmite owns the tradmark. Did they discontinue
them? What happened?

Both ohmite and sei/stackpole still offer NI variant wirewound
resistors through distribution. Vishay have them too (NS NH from
Dale).

Some types in the Digikey catalog
Ohmite WNseries to 2W axial
Vishay NH series to 250W plate-mounting.

I recon there must be better non-inductive alternatives..

Is it ayrton-perry or aryton-perry? Seems to be some confusion there.
Always thought it was the first. BOTH are used in the Ohmite catalog.

RL
 
T

The Phantom

Jan 1, 1970
0
Re: Sprague KoolOhm, low-inductance jelly-bean power resistors from a
bygone era



Nobody has responded to my post, so I'm emphasizing:
Sprague's famous Koolohm molded power resistors were
popular for decades, and were famed for performance
other resistors couldn't equal.

I've been measuring the self-inductance of all kinds
of wire-wound power resistors. Series inductance is
the parameter that limits the usefulness of modern
wire-wound resistors in many applications, from high-
current pulsing to H-bridge monitoring to RF to
vacuum-tube transmitter stages (oops)...

How about some numbers? What inductances are you measuring and at what
frequency? Which resistors gave which numbers?
 
W

Winfield

Jan 1, 1970
0
The said:
How about some numbers? What inductances are you measuring
and at what frequency? Which resistors gave which numbers?

Big question, but I'll try to give some short answers.
Most power resistors are wirewound types. Exceptions
are wire-strip resistors with values below 0.3 ohms,
carbon-composition resistors, some metal oxide types,
and ceramic-composition resistors (rare). I eliminate
common film types, etc, from this list, because they
cannot handle high pulse-power or surge levels.

Unless they use a special winding technique, such as
Aryton-Perry, wirewound resistors have high inductances
compared to composition types, and typically become
inductive above 5-15MHz (1 to 5W parts with values
above 20 ohms) or above 0.5 to 5MHz (for values from
1 to 20 ohms). For example, standard 3-ohm wirewound
resistors I measured became inductive as low as 430kHz
(1.17uH for an Ohmite 10-watt part) to 2MHz (275nH for
an IRC 3-watt AS-2 part).

A 5-watt Sprague KoolOhm part measured 48nH, or about
10MHz, which is 5 to 20x better than those others. A
2-watt 3 ohm carbon is 2-3x better yet, about 20MHz.
A straight wire, bent and fixed in the same position
as the 2W carbon, had nearly the same inductance, 14nH.

Well, I am finding some low-inductance parts, even in my
own inventory. For example, DigiKey stocks Yageo's low-
cost RSF metal-oxide series, but only in the 1 and 2-W
sizes (Yageo makes them from 1/2W to 5W). In contrast,
the KoolOhm resistors went to 10 and 20W or thereabouts.
The cool thing about KoolOhm was that they were low-cost
standard high-power parts, yet you got low-inductance
Aryton-Perry windings, or the equivalent.
 
F

Fred Bloggs

Jan 1, 1970
0
Winfield said:
Does anybody know what became of the Sprague
KoolOhm non-inductive power-resistor line -- who
owns it now, what did it evolve into?

I'm sure somebody knows...
I don't think Vishay got the line, since apparently
Ohmite owns the tradmark. Did they discontinue
them? What happened?

There is an interesting history of Zandman and Vishay ( named after his
hometown in Lithuania) at www.fundinguniverse.com which covers a little
of the demise of Sprague. Sprague was just getting into semiconductors
at the time the founder R.C. Sprague retired in 1962 and his son took
over. It was a disaster from that point on with the company losing
hundreds of millions attempting to develop a semiconductor business.
Sprague ownership then passed to General Cable and from there to Penn
Central Railroad of all things. Penn Central eliminated everything
except for the capacitor product lines. That's all that was left when
Vishay moved in, looking to expand into the capacitor market, possibly
unimpressed with KoolOhm design or market share, although that
particular product may have been liquidated prior to Vishay's run to
take over the entire world of component manufacture.
 
W

Winfield

Jan 1, 1970
0
legg said:
Both ohmite and sei/stackpole still offer NI variant
wirewound resistors through distribution. Vishay have
them too (NS NH from Dale).

Some types in the Digikey catalog
Ohmite WNseries to 2W axial

Yes, I have some of the WN series, sadly DigiKey carries
only a few values, and the most interesting ones are out
of stock. In the 1-watt and below region, there are lots
of interesting surface-mount resistors. It's the higher
power levels and 0.4 to 100-ohm region that's difficult,
expensive, and hard to find in stock. KoolOhm, R.I.P.
Vishay NH series to 250W plate-mounting.

$100 is too expensive (Newark) for a Jellybean resistor!

But I like RCD's non-inductive HPD series, in TO-220 and
TO-247 cases, $6.50, etc., at Newark. Say, why does a
50-watt TO-220 power resistor cost more than a highly-
sophisticated 50W power MOSFET? Sometimes it makes sense
to rig a way to replace the power resistor with a MOSFET.
I recon there must be better non-inductive alternatives..

Let's keep looking.
Is it ayrton-perry or aryton-perry? Seems to be some confusion there.
Always thought it was the first. BOTH are used in the Ohmite catalog.

Aryton-Perry, I think, caps because they were two blokes.
 
F

Fred Bartoli

Jan 1, 1970
0
Le Wed, 07 Nov 2007 04:27:17 -0800, Winfield a écrit:
Yes, I have some of the WN series, sadly DigiKey carries only a few
values, and the most interesting ones are out of stock. In the 1-watt
and below region, there are lots of interesting surface-mount
resistors. It's the higher power levels and 0.4 to 100-ohm region
that's difficult, expensive, and hard to find in stock. KoolOhm,
R.I.P.


$100 is too expensive (Newark) for a Jellybean resistor!

But I like RCD's non-inductive HPD series, in TO-220 and TO-247 cases,
$6.50, etc., at Newark. Say, why does a 50-watt TO-220 power resistor
cost more than a highly- sophisticated 50W power MOSFET? Sometimes it
makes sense to rig a way to replace the power resistor with a MOSFET.


Let's keep looking.


Aryton-Perry, I think, caps because they were two blokes.

Vishay, NS010 10W, 50 ohm 1% is stocked at mouser. $3

Lots of other (unfortunatly unstocked) values.
 
W

Winfield

Jan 1, 1970
0
Fred said:
Vishay, NS010 10W, 50 ohm 1% is stocked at mouser. $3

That sounds like a very useful part. Do we have
the part number right, I can't get it to come up.
 
W

Winfield

Jan 1, 1970
0
That sounds like a very useful part. Do we have
the part number right, I can't get it to come up.

Nevermind, you said Mouser! I looked up DigiKey.
 
J

John Fields

Jan 1, 1970
0
Big question, but I'll try to give some short answers.
Most power resistors are wirewound types. Exceptions
are wire-strip resistors with values below 0.3 ohms,
carbon-composition resistors, some metal oxide types,
and ceramic-composition resistors (rare). I eliminate
common film types, etc, from this list, because they
cannot handle high pulse-power or surge levels.

Unless they use a special winding technique, such as
Aryton-Perry, wirewound resistors have high inductances
compared to composition types, and typically become
inductive above 5-15MHz (1 to 5W parts with values
above 20 ohms) or above 0.5 to 5MHz (for values from
1 to 20 ohms). For example, standard 3-ohm wirewound
resistors I measured became inductive as low as 430kHz
(1.17uH for an Ohmite 10-watt part) to 2MHz (275nH for
an IRC 3-watt AS-2 part).

A 5-watt Sprague KoolOhm part measured 48nH, or about
10MHz, which is 5 to 20x better than those others. A
2-watt 3 ohm carbon is 2-3x better yet, about 20MHz.
A straight wire, bent and fixed in the same position
as the 2W carbon, had nearly the same inductance, 14nH.

Well, I am finding some low-inductance parts, even in my
own inventory. For example, DigiKey stocks Yageo's low-
cost RSF metal-oxide series, but only in the 1 and 2-W
sizes (Yageo makes them from 1/2W to 5W). In contrast,
the KoolOhm resistors went to 10 and 20W or thereabouts.
The cool thing about KoolOhm was that they were low-cost
standard high-power parts, yet you got low-inductance
Aryton-Perry windings, or the equivalent.
 
L

legg

Jan 1, 1970
0
Re: Sprague KoolOhm, low-inductance jelly-bean power resistors from a
bygone era



Nobody has responded to my post, so I'm emphasizing:
Sprague's famous Koolohm molded power resistors were
popular for decades, and were famed for performance
other resistors couldn't equal.

I've been measuring the self-inductance of all kinds
of wire-wound power resistors. Series inductance is
the parameter that limits the usefulness of modern
wire-wound resistors in many applications, from high-
current pulsing to H-bridge monitoring to RF to
vacuum-tube transmitter stages (oops)...

So far I've failed to find parts to equal these old
beauties, within a factor of 10 or more in most cases,
and so I wonder what's become of them. I'm asking
what we're all supposed to be using now. Consider:
the appealing thing about them was they were standard,
readily available parts, not special-order Aryton-Perry
windings with a high price and 1k minimum orders, etc.

I've got a few answers, but I really want to hear from
ya'll out there first. Somebody knows what went down,
and I'm eager to hear about it.

I think it's been quite a while since you could order non-inductive
Sprague resistors off the shelf. NI windings were always special
order.

Don't these wound things begin to look capacitive - Ayrton-Perry
having starts and finishes wound adjacent to one another on a fairly
large body?

It might be cheaper and more versatile to construct your own
non-inductive power pattern using penny smd parts on FR4

I had samples once of porcelain-on-steel thick film resistors that
you might look at.

http://www.rcdcomponents.com/rcd/rcdpdf/TP-TPS-FA048.pdf

You might arrange to get some kind of special terms, if you're
ordering for an educational facility - good targeted advertising.

http://www.welbornelabs.com/mills.htm

http://www.heiresistors.com/ovalstan.htm

http://www.upe-inc.com/resistors/

http://www.globar.com/ec/resistor.php.html

http://www.micro-ohm.com/powerceramic/ce.html

http://www.peccomponents.com/powerresister.htm?gclid=CMH7s83cyY8CFQS4hgod9RfEyw



RL
 
J

Joerg

Jan 1, 1970
0
Winfield said:
Does anybody know what became of the Sprague
KoolOhm non-inductive power-resistor line -- who
owns it now, what did it evolve into?

I don't think Vishay got the line, since apparently
Ohmite owns the tradmark. Did they discontinue
them? What happened?

Only the caps are left of Sprague. To me it all looked like a major
corporate shriveling-up process. Maybe one of those 3rd generation
downfalls.

I used to buy Dale for low-L resistors, they come in a heatsink
mountable enclosures:

http://www.vishay.com/docs/50013/rh.pdf

Look for N, NI parts that are low-L, maybe they are low enough for what
you need to do.
 
T

The Phantom

Jan 1, 1970
0
Big question, but I'll try to give some short answers.
Most power resistors are wirewound types. Exceptions
are wire-strip resistors with values below 0.3 ohms,
carbon-composition resistors, some metal oxide types,
and ceramic-composition resistors (rare). I eliminate
common film types, etc, from this list, because they
cannot handle high pulse-power or surge levels.

Unless they use a special winding technique, such as
Aryton-Perry, wirewound resistors have high inductances
compared to composition types, and typically become
inductive above 5-15MHz (1 to 5W parts with values
above 20 ohms) or above 0.5 to 5MHz (for values from
1 to 20 ohms). For example, standard 3-ohm wirewound
resistors I measured became inductive as low as 430kHz
(1.17uH for an Ohmite 10-watt part) to 2MHz (275nH for
an IRC 3-watt AS-2 part).

What do you mean, they "become" inductive? All my wire wound resistors
are inductive from the lowest frequency, achieving a (very low Q) series
resonance at some higher frequency, where they are capacitive for a while.
A 5-watt Sprague KoolOhm part measured 48nH, or about
10MHz, which is 5 to 20x better than those others.

I don't understand "...measured 48 nH, or about 10 MHz...". Do you mean
"...measured 48 nH, AT about 10 MHz..."?

Why don't you sacrifice (sob!!) one of your Koolohms and see how it's
built?
A
2-watt 3 ohm carbon is 2-3x better yet, about 20MHz.

Again, I don't understand. What is happening at 20 MHz?
 
J

john jardine

Jan 1, 1970
0
Winfield Hill said:
Does anybody know what became of the Sprague
KoolOhm non-inductive power-resistor line -- who
owns it now, what did it evolve into?

I don't think Vishay got the line, since apparently
Ohmite owns the tradmark. Did they discontinue
them? What happened?
Farnell stock as standard, the planar, non inductive, thick film types,
BPC(Bi tech) and (Tyco) MCP. These are quite cheap and have proved
surprisingly rugged.
 
W

Winfield

Jan 1, 1970
0
The said:
What do you mean, they "become" inductive? All my wire wound
resistors are inductive from the lowest frequency, achieving a
(very low Q) series resonance at some higher frequency, where
they are capacitive for a while.

Now, now, you know exactly what I mean. Low-value power
resistors are well characterized as a resistance in series
with an inductance. They "become" primarily inductive
above f = R / 2pi L, where the inductive reactance exceeds
the resistance.
I don't understand "...measured 48 nH, or about 10 MHz..."
Do you mean "...measured 48 nH, AT about 10 MHz..."?

No. A good LCR meter will show the same value for series
inductance over a wide range of measuring frequencies (to
be sure of the measurements, I do a quick check to verify
that I'm measuring with a high enough frequency to get a
sizable phase shift from the inductance, e.g. 5MHz or more
if needed). --- Sorry, here's a missing datum, the 48nH
measurement was on a 3-ohm 5-watt KoolOhm resistor, so
f = 3 / 2pi*48nH = 13MHz. Oops, where'd 10MH come from?
That was from an earlier 66nH measurement, except after
re-zeroing the meter I got 48nH. There are just too many
numbers floating around. :)
Why don't you sacrifice (sob!!) one of your Koolohms
and see how it's built?
Yep!

L = R / 2pi f = 23nH, or 2x better than 48nH (another
measurement yielded 66nH, hence the 2x - 3x estimate).

The carbon is close to a piece of similarly-shaped wire.
Again, I don't understand. What is happening at 20 MHz?

The breakpoint frequency. It's convenient to say the part
acts primarily as a resistor until a 3dB point, afterwhich
it acts primarily an an inductor. Plot Z vs. frequency: a
straight line from DC to a breakpoint, then rising with f.
You know the drill, I assume.
 
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