Which resistor type for emitter resistor?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I'm working on my new hybrid amplifier. It will use 0R22 ohm emitter resistors. I don't want to use cheap and bad sounding types. I checked some Welwyn, Sfernice, Beyschlag types, but I have no experience with any of them. Any advice?
Please avoid the very expensive types, because I need 32pcs. for one stereo amplifier (2x900W/2ohms)

Sajti
 
why wind your own. You can buy Nichrome resistance wire, and measure how much you'll need to obtain desired resistance, cut all pieces to that length, and solder in place. Will be much more open sounding than the ceramic power resistors that are commonly used.
 
pjp said:
you'll get a resistor whose resistance varies all over the place as soon as you pass current through it.
"all over the place" or follows the temp coeff?

According to this table:
TEMPERATURE COEFFICIENTS OF RESISTANCE, AT 20 DEGREES C


Material Element/Alloy "alpha" per degree Celsius
==========================================================
Nickel -------- Element --------------- 0.005866
Iron ---------- Element --------------- 0.005671
Molybdenum ---- Element --------------- 0.004579
Tungsten ------ Element --------------- 0.004403
Aluminum ------ Element --------------- 0.004308
Copper -------- Element --------------- 0.004041
Silver -------- Element --------------- 0.003819
Platinum ------ Element --------------- 0.003729
Gold ---------- Element --------------- 0.003715
Zinc ---------- Element --------------- 0.003847
Steel* --------- Alloy ---------------- 0.003
Nichrome ------- Alloy ---------------- 0.00017
Nichrome V ----- Alloy ---------------- 0.00013
Manganin ------- Alloy ------------ +/- 0.000015
Constantan ----- Alloy --------------- -0.000074

http://www.allaboutcircuits.com/vol_1/chpt_12/6.html

Nichrome has a lot less change in resistance than copper at room temperature.

Nickel and Chromium atoms have the same electron seating arrangement (shell structure) as Nickel and Copper - hence Nichrome also has a wide temperature range where resistance does not change.
from
http://www.seed.slb.com/v2/FAQView.cfm?ID=397
 
There's nothing wrong with nichrome, but it's difficult or impossible to solder. Commercial resistors have certainly been made from it, but the leads would be spot welded. That's also true of the best modern resistance alloys- they have to be spot welded. I like Manganin because it's the original precision resistance alloy with low temperature coefficient, low thermal emf against copper, and you can solder it with ease. I've also made lots of resistors out of Constantan. It's only slightly harder to solder, has a good TC, but much higher thermal emf against copper- that's why it's used as thermocouple wire. That's also why it's very easy to get.

Though you can often get away with a short piece of fine gage resistance wire, and no coil at all, you're trying to make a resistor, not a fuse. You may want to go a bit heavier, hairpin the wire, then make a couple coils to keep the size down. The power handling will be much greater.
 
Magura, I'd try Omega Engineering, but anybody that sells thermocouple stuff will have it. I don't know if it applies to Constantan, but there's often two grades of wire, primary and extension wire. Extension wire is fine for resistors. Constantan is also sold under a variety of house names. Jelliff Alloy 45 is one of them, but Google should turn up lots of suppliers. Kanthal Palm Coast is another one- I've gotten Manganin from them in years past as well.
 
Conrad Hoffman said:
Magura, I'd try Omega Engineering, but anybody that sells thermocouple stuff will have it. I don't know if it applies to Constantan, but there's often two grades of wire, primary and extension wire. Extension wire is fine for resistors. Constantan is also sold under a variety of house names. Jelliff Alloy 45 is one of them, but Google should turn up lots of suppliers. Kanthal Palm Coast is another one- I've gotten Manganin from them in years past as well.


Thanks.



Magura :)
 
If you tin the ends of the wire with pure silver solder you should not have too hard of a time working with the resistors after that. The wire is made for high temp applications and should withstand the initial silver melting temperature. After tinning the silver will be easy to solder with conventional low temp solder for electronics. You will need a good silver flux and a clean flame.
The question that comes next is will the resistance change even with conventional solder as it wicks up the wire. Your length of nichrome or whatever is now contaminated along its length by a new substance with different properties. This sounds like a tedious bit of hard work.

Personally I like Mills resistors. They are expensive but you only need a few for the emitters. They are designed for audio signals.

Tad
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.