NAD 3150

[poundy]

mmm i will,eventualy, trouble is i have 17 nads yet to fix 😱

 

[poundy]

The lamp will glow when you have bias current flowing. So not a problem.

Just remember to make sure the adjustment is still correct when on full mains as it can change with the higher supply voltage.

The centre pin of the resistor pack will go to the speaker output and so measuring from speaker + to that centre pin would always show as 0 volt. If the manual says to do it that way then it is wrong. You have to measure across one of the resistors which you seem to be doing.

8mv will about 36 milliamps current

A buzz 😀 a loud buzz, a quiet buzz. It needs quantifying and checking. Does it change with the volume control for example.

oh by the way the buzz dissapeared with those 10 loose joints😉

 

[poundy]

If the resistor is in series with a relay coil, sitting there running hot day in and day out, it could turn brown into violet easily. Discoloration is a sign of long term (over)heating. And if it does read 490 ohms that pretty much confirms that it’s running too hot - values tend to go *up*. Probably using 1/2 watt carbon film when they really needed 2 watt MOX or WW for long term stability.

it was def a 2w carbon installed

 

[wg_ski]

Carbon comp? Long term stability = crap. Par for the course.

mmm i will,eventualy, trouble is i have 17 nads yet to fix 😱

You’re going to be busy for the rest of your natural life.

 

[poundy]

ive already been busy for the first bit 😀

 

[poundy]

Carbon comp? Long term stability = crap. Par for the course.



You’re going to be busy for the rest of your natural life.

sorry yes composite

 

[Mooly]

mmm i will,eventualy, trouble is i have 17 nads yet to fix 😱

So that is why the price has increased, shortage of supply 'cos someone is buying them all up 😀

oh by the way the buzz dissapeared with those 10 loose joints😉

Well that's good 🙂

sorry yes composite

Composite as in carbon composition... NAD use those things? Carbon film is fine but not the other. That's very 1960's.

Carbon composition, you could keep it original:

 

[poundy]

no they don't look like that ,not the 2-4w ones anyway.
they are all one colour, blue mainly and have the resistance written on them

they are quite crumbly if you pick at them

 

[wg_ski]

Those all blue ones are metal oxide. If they are “crumbly” then they are of poor quality. Even the cheap Yageo ones I use hold together quite well - even when overloaded.

 

[poundy]

your quite right they are
funny one service manual says metal film the other metal oxide

 

[Mooly]

Metal oxides were used a lot in older TV's as they are good at withstanding high temperatures and demanding spiky fast risetime voltages that were often encountered.

 

[poundy]

i take it they are not realy used these days then, replaced with film?

 

[Mooly]

More a case that the applications that used them have disappeared I think. Things such as line output stages on CRT based TV's although they do still turn up in switching power supplies which see the same very high voltage very fast rise time pulse waveforms. Thy do have their uses still.

 

[poundy]

i must admit i dont see them in anything i work on after about 85'

 

[Mooly]

You won't find many in audio gear, there is just no need to use them for these applications.