Good day all,
I build this amplifier.Issue is after warp up 2 hours amp heatsink is 52degree and transformer 100++degree.i use 35vdc supply.in my mind maybe bias is high.can anobody suggest:
1.how to cek bias
2.how to add pot to tuning bias
Or correct this circuit.
I build this amplifier.Issue is after warp up 2 hours amp heatsink is 52degree and transformer 100++degree.i use 35vdc supply.in my mind maybe bias is high.can anobody suggest:
1.how to cek bias
2.how to add pot to tuning bias
Or correct this circuit.
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Place a 1k pot across D1 to bring the quiescent current down.
The output FETs can start to conduct with just 0.15v Gate to Source.
The output FETs can start to conduct with just 0.15v Gate to Source.
Thanks for reply Mr JonSnell,
Just for confirm,1k pot like picture?
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That circuit is pretty much the same as Hitachi app note for lateral mosfets.
Except it has two diodes for bias where app note had 1K trimmer.
I found they need very little bias to work.
The original circuit was well tried and tested. Maplin sold hundreds of that circuit.
Hi all.
After add 2k pot on D1(i dont have 1k pot).
My emitter voltage decrease from 22mV to 11mV. And heat sink temperature become less hot🙂..
But i measure 4 emitter voltage result is:
11.1mv
6.1mv
-9.5mv
-7.9mv
Which one i need to focus to trim pot for bias 50mA?
My emitter resistor value is 0.22ohm.
After add 2k pot on D1(i dont have 1k pot).
My emitter voltage decrease from 22mV to 11mV. And heat sink temperature become less hot🙂..
But i measure 4 emitter voltage result is:
11.1mv
6.1mv
-9.5mv
-7.9mv
Which one i need to focus to trim pot for bias 50mA?
My emitter resistor value is 0.22ohm.
Attachments
On the Maplin lateral mosfet they put a multimeter set to mA in series with positive power rail. The bias was turned up slowly until reached 100mA.
you measure each emitter resistor 0.22ohm voltage around 11mv, each mosfet bias current will be 50mA, you can set the VR to get this voltage.
Thanks for reply. Hope we all safe and strong in covid19 situation.
Yes i already tune using VR. My question is 4 resistor have 4 difference value. Is this normal? Or i need select lowest value of Resistor for tuning?
So you mean i need use another way to set bias. As i remember need put 100ohm resistor on power rail and measure that resistor voltage. Maybe i try later. Hopr somebody can teach me for detail using this way.
The Maplin lateral amp didnt have source resistors so had to be done a different way. You clearly have so just use volt drop across a source resistor to set bias current.
This is normal, you just watch the lowest resistor voltage reach 11mv, others over 11mv is ok.
I already insert 100ohm on both power rail.
And measure positive dc voltage. What for best voltage i need to set for my current amp?
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Mr nigel, what exact value across 100ohm resistor? Can you give some formula? Easy to me understand how many current need for each fet. Thanks