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Old 22nd September 2012, 12:48 AM   #1
wanders is offline wanders  United States
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Default Resistor Alternative

In replacing a large can capacitor in my McIntosh C24 preamp, I burned out a 2.2k, 1w, carbon resistor that was attached to the old cap. It will be next week before I can get the correct part, but I'm very close (I think) to getting the unit operational and I don't want to wait for the part. I stopped by a Radio Shach and purchased two alternatives: 1) a 2.2k, 1/2 w carbon film, or 2) I can string together two 1k, 1w, plus two 100 ohm, 1w, medal oxide resistors. (1k + 1k + 100 + 100.) This would be a temporary fix until I get the right component.

I'd appreciate thoughts on which to use.

Thanks
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Old 22nd September 2012, 05:59 AM   #2
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Use option 3) two 2.2k 1/2W in series, paralleled with another two 2.2k in series.
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Old 22nd September 2012, 07:02 AM   #3
jitter is offline jitter  Netherlands
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1) No. McIntosh didn't use a 1 W resistor just for fun, so you're 1/2 W resistor might be overloaded.

2) Yes, this should work.
Since power is dissipated in four resistors instead of one, they might even be less than 1 W. For the 1k resistors, 1/2 W should suffice, for the 100R resistors 1/8 W is sufficient.

3) Yes, if the power the 2k2/1W resistor was designed to dissipate is somewhat less than 1 W (likely), this should work.
Because of tolerances, currents flowing through the parallelled resistors, aren't equal. Though, this is of little concern if the actual dissipation in the 2k2/1W resistor is not very close to 1 W.

Last edited by jitter; 22nd September 2012 at 07:07 AM.
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Old 22nd September 2012, 08:20 AM   #4
AndrewT is offline AndrewT  Scotland
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two 4k7//4k7 or three 6k8//6k8//6k8 or etc.....
or 1k1+1k1 or 390r+390r+390r or etc....

All will give roughly 2k2 and of higher dissipation rating.
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Old 22nd September 2012, 10:58 AM   #5
wanders is offline wanders  United States
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Appreciate all advice.

Quote:
Originally Posted by sofaspud View Post
Use option 3) two 2.2k 1/2W in series, paralleled with another two 2.2k in series.
Wouldn't two 2.2k in series produce 4.4 ohms resistance?
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Old 22nd September 2012, 11:12 AM   #6
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Did you forget a "k"? You end up with two 4.4k ohm series pairs in parallel for 2.2k ohm effectively. And power is more or less split across four resistors.
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Old 22nd September 2012, 12:53 PM   #7
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Quote:
Originally Posted by wanders View Post
Appreciate all advice.



Wouldn't two 2.2k in series produce 4.4 ohms resistance?
yes you are correct.
but if you parrallel 2.2k with 2.2k both 1W you end up with a 1.1kohm 2W resisitor.
add the same up again and series and 2.2k higher wattage....
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Old 22nd September 2012, 12:56 PM   #8
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woops.... sofa posted nevermind.
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Old 22nd September 2012, 01:07 PM   #9
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This reminds me of the; If you had a 5 and a 3 gallon bucket how do you measure out 4 gallons of water?

Not at all suggesting using a lesser rated part, but out of curiosity (because sometimes there are other constraints or desires) is it possible to post a partial schematic or sketch of how this 2.2K resistor is used?

Just re-read your original post where it seems possible this resistor is a bleeder across the large bulk cap, this would dissipate approximately half its rating for a 33V supply, or maybe its just part of a shunt regulator.


Many thanks
-Antonio

Last edited by magnoman; 22nd September 2012 at 01:14 PM. Reason: Read post again
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Old 22nd September 2012, 03:03 PM   #10
djk is online now djk
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The resistor is part of a CRCR filter feeding the 75V regulator for the entire B+ load.

Assume 10ma total current to be supplied, that would require 0.22W and a 1W part would be what I would use in that position.
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