LEAK PLUS 30 IQL IQR adjustment

[pentoad]

How do you do this with DMM or AVO if you don't have an ammeter and you don't want to play around with those "current links"?
I have included an attachment which has the instructions.

[GrimJosef]

Depending on which DMM you have it may well have an ammeter capability.

Harold Leak wasn't the sort of chap who put unnecessary things into his circuits (they cost money, and he cared about his money). So given that he's made the current links available they'll be there for a reason, which is probably that that's the easiest and most reliable way of measuring what you need to measure.

It seems from the circuit though, assuming it's this one https://www.angelfire.com/sd/paulkemble/sound7h.html, that there's also a 1ohm resistor, R56, in the relevant transistor's emitter circuit. if you measure the voltage across this then Ohm's Law will let you work out the current through it. That will be the collector current (which the instructions say should be set to 15-20mA) plus the base current. Strictly speaking we don't know how big the base current is, but it should be relatively small compared with the collector current so an approximation would be to neglect it and to set the controls for 15-20mV across R56. That would also involve assuming that R56 really is 1ohm.

So, we could get an approximate answer (neglects base current) which might be a bit wrong (if R56 isn't 1ohm). Or we could do the job as instructed.

Cheers,

GJ

[Electronpusher0]

You could try opening the link as instructed and inserting a 10 ohm resistor instead.
This will drop 100mV for 10mA so 30mA will drop 300mV. That level of drop will not affect the amplifier (when Quiescent) but allows you to connect a dmm across the 10 ohm on the 1V range and read 0.3V for 30mA

If your dmm has a mV range then you could measure across the emitter resistors R56 or R57 (1 ohm) instead of opening the links. That depends on the value of R56 and R57 having not drifted in value.
30mA across the 1ohm gives 30mV

Peter

Edit crossed with GJ, at least we agree.....

[snowman_al]

Measure the Voltage across the 0.5Ω resistors R52 or R53.
A voltage of 0.015 volts (15 milli volts) equates to 30mA current, by ohm's law.
Check both they should be very similar. Be careful to insulate the tips of your probes and take care not to short anything out taking the measurements...

Err, are we talking about the Stereo 30 or Stereo 30+ (plus) they are different? I've answered assuming it is a 30+.

[Electronpusher0]

True, R56 is 1 ohm on the stereo 30.

Peter

[pentoad]

It is the stereo 30 plus

[Electronpusher0]

Then SnowmanAl's advice in post 4 applies.

Peter

[pentoad]

Originally Posted by Electronpusher0

Then SnowmanAl's advice in post 4 applies.

Peter

Thank you to all, I will proceed as advised by SnowmanAl