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Old 22nd September 2012, 11:29 AM   #3121
naf is offline naf  Indonesia
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Yes 1K+220 is perfectly OKAY(I am doing this too). In fact, you may need to modify these values after checking the initial bias, which may not be optimum at first.

Board looking good with parts.
Thank you Shaan,
Ok, i'll go with series resistor.
Anoter question do i need little heatsink on BD139/140?
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Old 22nd September 2012, 02:12 PM   #3122
shaan is offline shaan  India
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Do i need little heatsink on BD139/140?
Yes. 1"x1" heatsink will do. I used "U" shaped small heatsinks which aren't too good, a little more hotter than I like. But I did this so that the VAS bias would stabilize quickly.
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Old 22nd September 2012, 02:22 PM   #3123
shaan is offline shaan  India
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Hi naf. The zeners seem to me to be 1/2 watt rated. You should use a 1watt one.

With 470ohm feed resistor, the dissipation is over 400mW; although less than 500mW, having a larger dissipation margin is good for long term reliability as 1W zeners have thicker wires that can help transfer much of the heat to the copper quickly.
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Old 22nd September 2012, 03:04 PM   #3124
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Shaan. thanks for your information, i'll paralell the zener and add little heatsink to VAS tr.
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Old 22nd September 2012, 03:41 PM   #3125
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i'll paralell the zener
??
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Old 22nd September 2012, 03:55 PM   #3126
shaan is offline shaan  India
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I'll paralell the zener.
NO NO NO! DON'T!

Read this to know why you should not:- Can you parallel zener diodes?
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Old 22nd September 2012, 04:01 PM   #3127
naf is offline naf  Indonesia
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??
dear Esperado,
as i'm new to this electronic world.
i think by paralelling the zener it will increase watt rated, just like paralelling elco to increased capacitance.

edit:
Shaan gave me link about paralelling the zener, now i know why.

Last edited by naf; 22nd September 2012 at 04:14 PM. Reason: correction
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Old 22nd September 2012, 04:03 PM   #3128
naf is offline naf  Indonesia
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NO NO NO! DON'T!

Read this to know why you should not:- Can you parallel zener diodes?
thank you Shaan, now it's clear to me.
i learn something new.

Last edited by naf; 22nd September 2012 at 04:15 PM.
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Old 22nd September 2012, 04:18 PM   #3129
shaan is offline shaan  India
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thank you Shaan, now it's clear to me.
i learn something new.
Happy to help.
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Old 23rd September 2012, 09:21 AM   #3130
naf is offline naf  Indonesia
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Shaan, here my progress on building..
sorry don't have chance to source 1W zener :-(
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