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Old 27th January 2006, 02:33 PM   #1
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Default Emitter Resistors

What would be a good choice for emitter resistors in a 50W-100W design?
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Old 27th January 2006, 02:54 PM   #2
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Anything in the range 0.1 ohm to 0.47 ohm, it's a trade off of temperature stability and distortion. Higher the resistance better the temp stab.
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Old 27th January 2006, 04:59 PM   #3
CBS240 is offline CBS240  United States
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One must consider Zout when choosing this value.
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Old 27th January 2006, 05:15 PM   #4
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Not really, since they are inside the negative feedback loop.
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Old 27th January 2006, 07:41 PM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
for your range of power it looks like a 1pair or 2pair output stage is suitable.
I suggest about 3W wire wound.

I have seen on this forum a suggestion that the emitter resistors should be non inductive but I cannot confirm this.
If non inductive is important then wirewound is not suitable unless they are specially wound to eliminate inductance. I believe a few manufacturers can supply this specification.
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Old 27th January 2006, 10:02 PM   #6
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It is neither expensive nor particularly complicated to make them non-inductive if one does that this way as I am doing last 20+ years. If you use metal-film 1% 1/2W resistors, this way you have practically non-inductive 5W resistor that occupy les space and is much cheaper than some exotic "audiophile-grade" types. Please note that there are TWO emitter resistors of 0,1 ohm on the picture! This might be useful idea for someone.
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Old 27th January 2006, 11:17 PM   #7
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Default RCD

I just bought a lot of 100 RTD135, 0.4 Ohm, 3W for $12.00. Think they will work OK?
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Old 27th January 2006, 11:26 PM   #8
anatech is offline anatech  Canada
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Hi hawkfeather,
Yes. As long as the value is okay. Are they the flat "plate" low inductance resistors?

-Chris
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Old 28th January 2006, 12:02 AM   #9
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Default RCD info...

Hey Chris...

I'm attaching the data sheet... seems like they are pretty decent ones. Guess I got a good deal after all!
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Old 28th January 2006, 12:32 AM   #10
anatech is offline anatech  Canada
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Hi hawkfeather,
Quote:
INDUCTANCE: small sizes have inductance of 1- 50uH typ.
May or may not present a problem.

-Chris
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