Hi All,

I have what appears to be cement power resistors marked zero (0) ohms. They are in the output stage of a subwoofer amplifier that failed before its time (less than 3 years).

The amp failed in the wee hours of the morning some months ago, some hours after I left it powered up after turning off the signal source (our TV receiver).

The way that I could tell was that it sounded like a jet engine was going through field testing upstairs. At least to my sleep muddled ears!

Here's what the components look like:

I apologize for the blanked background. I took this image on my very cluttered workbench, and decided all of the cruft in the background was distracting.

There were two resistors with these markings in this amplifier. Both of them occur between power transistor pairs, as the PCB shows. The transistors are on the bottom side to allow heat sink contact.

I looked up the SQF 55 ceramic resistors online, and found their specifications:

However, this table shows that they have a minimum value of 0.1 Ohms.

My questions:
1) Am I reading the value correctly?
2) Anyone have an idea what purpose these serve in an audio output stage? Short circuit or overload protection perhaps? I looked up zero ohm resistors, and they claim to be used for current measurement and as links.

I'm mainly curious, but I'm working on some projects and am not above scavenging parts... If they turn out to be usable.

Thanks much,

Scott C.

 

Hello,

It says 0Ω15 , wich means 0.15 Ω
The Ω-sign is used as the decimal point.

The purpose depends on where the resistor is used in the schematic.

Bertus

 

Likely they are current balancing resistors for the power transistors.
They are usable, but I can't remember seeing that range of resistance used for anything except current balancing and current sensing. If you foresee that kind of application in your crystal ball, keep them.

 

I was just looking in my junk box for a 0.1 or 0.5 resistor at 5 watts. It was for current sensing for a 12 volt motor powered by a lead-acid battery (about 15 amps).

Keep it.

I agree with #12 that one of these resistors likely connects the emitters of the output power PNP and another for the NPN going to the red output terminal to the speaker (there might be a relay between the junction of the two resistors before the red terminal).

 

a piece of wire will do

 

Thanks Bertus, I thought there was a trick to reading the value. Much appreciated.

Thanks also to #12 and GopherT for shining a light on what it's for.

Scott C.

 

It says 0Ω15 , which means 0.15 Ω
The Ω-sign is used as the decimal point.

A similar form of that is 0R15
That is from the form: 2K2 or 1M5 for 2200 ohms and 1 point 5 megohms.