500W PA amplifier with Limiter

[engel dela pena]

Originally Posted by apexaudio

Do not powering up without heatsink, drivers transistor work in class A.
Don't forget wire jumper on coper side pcb.
Don't forget to connect input GND.
Use 150R 20W on primar ac transformer.
U can use 100R instead fuses, I don't, but I made 1600 amplifiers still now.
Check DC offset before connect speakers, use 100uF bipolar if U want test amplifier without protect.
Good luck!
Regards

this is my heat sink
can i use step down transformer in testing since i don't have a variac
220v is our mains here i'm planning to step down to 110v,is this a good idea?
how about light bulb which is better to put in primary or in secondary?

[wg_ski]

If you use a light bulb limiter, you don't need to step it down first or use any DC protect. The light bulb is actually better than a variac. A lot of amplifiers will work perfectly at lower voltage and get unstable at full voltage. With a variac turned down it may behave, and then go bang very suddenly as it is brought up. The light bulb will let the amp get to 90% of normal voltage when it's idling, and bring it down automatically if it goes unstable.

[apexaudio]

Originally Posted by engel dela pena

this is my heat sink
can i use step down transformer in testing since i don't have a variac
220v is our mains here i'm planning to step down to 110v,is this a good idea?
how about light bulb which is better to put in primary or in secondary?

Just put 150R 10-20W in primary.

[apexaudio]

Originally Posted by wg_ski

If you use a light bulb limiter, you don't need to step it down first or use any DC protect. The light bulb is actually better than a variac. A lot of amplifiers will work perfectly at lower voltage and get unstable at full voltage. With a variac turned down it may behave, and then go bang very suddenly as it is brought up. The light bulb will let the amp get to 90% of normal voltage when it's idling, and bring it down automatically if it goes unstable.

I agree, but I don't use bulb, and can't suggest without my expirience. What will be bulb specify?

[andrewlebon]

hi engel dela pena
greetings use 100 watt bulb in series with primary winding

thanking you
andrew lebon

[apexaudio]

Bulb have positive temperature coefficient (PTC). When bulb is cold it have small resistance, when current rising bulb get hot and resistance is R=U2/P. U=220v, P=100w and R=484R when bulb bright, that resistance will drop voltage on primary and protect amplifier if something is wrong.
Resistance of 150R will drop voltage on primary if current rising. Voltage on primary will be U=220v-150RxI(A), voltage drop will protect amplifier is something was wrong also like bulb.

[electra_ina]

Originally Posted by engel dela pena

what particular ink are you using
that is not a ordinary silk screen embosed ink

I just print layout PCB, my friends is specially work in advertising which transfer in PCB. I don't know what ink in used..
Regards,

[elgafary]

goooooooooood

[apexaudio]

I don't see clear, but led must look directly to ldr, and light cause drop resistance of ldr.

[apexaudio]

Originally Posted by elgafary

goooooooooood

Give us some more words, what do you mean?