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pingfloid 17th March 2004 07:18 PM

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?

Cheers

fdegrove 17th March 2004 11:49 PM

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.

Cheers,;)

316a 18th March 2004 12:25 AM

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 ?

316a

fdegrove 18th March 2004 12:33 AM

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...

Cheers,;)

316a 18th March 2004 12:55 AM

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

Sch3mat1c 18th March 2004 02:29 AM

It only needs to be 5W

pingfloid 18th March 2004 06:32 AM

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? :rolleyes:

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/

Brian Clark 18th March 2004 09:43 AM

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 :)

Brian.

fdegrove 18th March 2004 11:47 AM

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,;)

hacknet 19th March 2004 02:13 AM

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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