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Old 17th March 2004, 06:18 PM   #1
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Default Choosing a suitable 50W cathode resistor

I am trying to find a 360 Ohm / 50W non inductive resistor for thisKT88 SE amp

Wich one would you choose from this list? (Vishai Components)

I think that maybe the RTO50 type would be ok, but there is also the RCH and RTOP that maybe could be fine.

What brand of resistors do you use for this purpose?

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Old 17th March 2004, 10:49 PM   #2
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Hi,

Quote:
What brand of resistors do you use for this purpose?
Jean Hiraga recommends Dale or Sfernice NI WW.
I think to Sfernice should be available in Spain and it wouldn't surpise me if they're part of the Vishay group of companis as well since Vishays' been gobbling up quite a lot of companies the past ten years.

The ones shown in the Vishay datasheet are thick film types, I never tried those but I hear WW is to be preferred.

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Old 17th March 2004, 11:25 PM   #3
316a is offline 316a  England
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Default Re: Choosing a suitable 50W cathode resistor

Quote:
Originally posted by pingfloid
I am trying to find a 360 Ohm / 50W non inductive resistor for thisKT88 SE amp

Wich one would you choose from this list? (Vishai Components)

I think that maybe the RTO50 type would be ok, but there is also the RCH and RTOP that maybe could be fine.

What brand of resistors do you use for this purpose?

Cheers
Hello ,
Why non-inductive , I would have thought a 50watt aluminium clad wirewound bolted to the chassis do the trick ? I believe the 'non inductive' metal film power resistors can be noisy but will inductance be an issue with a 360 ohm resistor ?

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Old 17th March 2004, 11:33 PM   #4
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Hi,

Quote:
Why non-inductive , I would have thought a 50watt aluminium clad wirewound would bolted to the chassis do the trick ?
Just like the HF correction cap across the primary of the OPT, the use of a non-inductive WW is part of the target here, namely to build a SE amp with as linear as possible response upto 100K Hz.

In his designs Jean Hiraga always recommends the use of non-inductive WWs.

Noise shouldn't be a big issue here as a NI WW should have no more than twice the noise of a regular WW resistor; 360 Ohm or 720 Ohm...

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Old 17th March 2004, 11:55 PM   #5
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Default Ah !

Quote:
Originally posted by fdegrove
Hi,



Just like the HF correction cap across the primary of the OPT, the use of a non-inductive WW is part of the target here, namely to build a SE amp with as linear as possible response upto 100K Hz.

In his designs Jean Hiraga always recommends the use of non-inductive WWs.

Noise shouldn't be a big issue here as a NI WW should have no more than twice the noise of a regular WW resistor; 360 Ohm or 720 Ohm...

Cheers,
...but yes 100kHz with SRPP ECC83 input stage ? More than marginal to say the least especially if the amp is preceeded by a passive line stage .

316a
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Old 18th March 2004, 01:29 AM   #6
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It only needs to be 5W
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Old 18th March 2004, 05:32 AM   #7
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Quote:
it wouldn't surpise me if they're part of the Vishay group
You're right Frank, both Dale and Sfernice are part of the Vishai group.
Does WW means WireWound? In that case they maybe inductive. Isn't it?

Sorry, my link to the Vishay was not the intended one. This is the correct one:

http://www.vishay.com/resistors-disc...ive/res10-10K/
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Old 18th March 2004, 08:43 AM   #8
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Quote:
Originally posted by Sch3mat1c
It only needs to be 5W
Hmm. 37.5 x 37.5 /360 = 3.9W. I would make sure that a 5W resistor is VERY well heatsinked running that close to spec since heating leads to derating

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Old 18th March 2004, 10:47 AM   #9
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Hi,

Quote:
Does WW means WireWound? In that case they maybe inductive. Isn't it?
WW means WireWound, the suffix NI stands for non-inductive.

That NI types are usually more than twice as expensive as the regular ones.
The way they arrive at cancelling out inductance is by coiling the ni-chrome wire twice, once going the other coming.
This is known as the Ayrton-Perry technique after its inventor.

Quote:
...but yes 100kHz with SRPP ECC83 input stage ?
Global NFB is applied and the amp does meet the target spec.

Quote:
I would make sure that a 5W resistor is VERY well heatsinked running that close to spec since heating leads to derating
That plus the fact that you need to consider fault conditions as well.

Cheers,
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Old 19th March 2004, 01:13 AM   #10
hacknet is offline hacknet  Singapore
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i`d prefer to use a couple of 2 watt carbon resistors in parallel. this way, you got no induction and you should be able to dissipate enough.

try maby 4 in parallel to be safe. value should be about 1.5k 2watts.
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