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Old 6th April 2013, 11:51 PM   #1
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Default power resistors in power amps

I am making a mouser order for general experimentation purposes. I have put a great many of suggested transistors in my cart, but now I need to make sure I have enough resistors.

In my tube amp component stash, I have a healthy supply of 2 watt metal oxide resistors, a similar stash of 1/2 watt metal film, and a decent pile of 5 watt wire wound.

I lack resistors below about 10 ohms, and really anything below 100 in much variety of values. I know that the emitter resistors in the output section are quite small, and need to have some degree of power handling, right?.

What would be a good selection of values/power ratings to get me going? Think 100 watts or less of output if that matters.
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Old 7th April 2013, 01:22 AM   #2
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Hi Dan
Emitter resistors discussed here: Emitter resistor at output stage transistor.

and Doug Self here: Distortion In Power Amplifiers
0.22R to as low as 0.1R at 5 watt are common values for this section of circuitry.


Cheers / Chris
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Old 7th April 2013, 03:20 AM   #3
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I'm looking for metal plate/element emitter resistors, but i can't find seller everywhere.
Why they don't longer produced?
Noble is very good, but no seller on the web.
Yageo have only a few value low too. Not good if you are many transistors parallel
Futaba can't find everywhere.
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Old 7th April 2013, 03:58 AM   #4
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Quote:
Originally Posted by Dan Moos View Post
I know that the emitter resistors in the output section are quite small, and need to have some degree of power handling, right?.
What would be a good selection of values/power ratings to get me going? Think 100 watts or less of output if that matters.
I've worked on an amp with MJ15024-25 output transistors that used two each 1 ohm 5 w in parallel to make .5 ohm @ 10 w on each output transistor. These were flameproof wirewound resistors, I believe. Other schematics I've looked at used .39 ohm 5 watt or .33 ohm 5 watt. The higher the emitter resistance, the less sensitive the amp is to matching the output transistors, IMHO. At least the amp I worked on that had the .5 ohm 10 w, the factory had stated any transistor bought from them with the right PN would work without matching.
I monkey with battery chargers and car ignition circuits also, and have found it convenient to keep around 1 ohm 25 watt and 2 ohm 20 watt resistors, also. A resistor in series with the diodes in a battery charger keeps from burning up a $100 power transformer if lightning shorts out the diode. And you can't buy ballast resistors for cars anymore from the auto supply that last more than a year outside: the crimped connections corrode over. I had to make a 1.6 ohm resistor with solder joints. The 12v battery chargers for sale now are full of electronic control gimmicks that you can't leave plugged up in a lightning storm.
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Last edited by indianajo; 7th April 2013 at 04:05 AM.
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Old 7th April 2013, 04:05 AM   #5
Zero D is offline Zero D  United Kingdom
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@ Walkalone

Here's one company who makes them WELWYN Just one example of many values etc available WH10 0R2 JI - WELWYN - RESISTOR, 15W 5% 0R2 | Farnell United Kingdom

WELWYN in CHINA Sales :: Welwyn TT & lots of other countries
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Old 7th April 2013, 08:31 AM   #6
hahfran is offline hahfran  Germany
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It seems that paralleling a bunch of metal film or even better carbon film resistors , carefully selected for equal resistance, yields a better sonic quality. For ex. 4 1 ohms parallel yield 0.25 ohms
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