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Old 4th November 2012, 04:35 PM   #661
44250 is offline 44250  Serbia
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Quote:
Originally Posted by nazirdigi View Post
hi apex sir,
can i use 500r pot instead 470r pot? because in here 470r pot is not god quality.
if yes what are the changes i have to make?
in what amplifier? if it is bias trim.pot. there should not be any trouble. to be sure,just decrease value of the resistor
in series with bias trim.pot for that 30 Ohm.
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Old 4th November 2012, 04:57 PM   #662
AndrewT is online now AndrewT  Scotland
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The tolerance of 500r pots and 470r pots effectively make them the same thing.
One swaps for the other.

+-10% gives a range for a 500r of 450r to 550r.
It is them adjusted to any value in that range when used as a trimmer.
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Old 5th November 2012, 01:44 AM   #663
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for apex hv25, the pot is for bias adjust.
so i have to decrease the 100 ohm resistor to 70 ohm, am i correct?
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Last edited by wattaniya; 5th November 2012 at 01:52 AM.
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Old 5th November 2012, 02:51 AM   #664
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There is no need to change R20.
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Old 5th November 2012, 04:55 AM   #665
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i changed 500r trim. for 1k trim. to get larger value of bias,with 500r it was to small. if that happens to you,set 100r resistor to a larger value,say 390r. if you get 30-50mA don't change anything.
.
have you matched all input 2n5551 and 2n5401 as close as possible? it has influence to a dc-offset
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Old 5th November 2012, 10:49 AM   #666
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thank u for the reply djk and 44250
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Old 5th November 2012, 04:31 PM   #667
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don't mention it.
.
.
it is important to match all input 2N transistors as close as possible,have you done it?
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Old 5th November 2012, 04:54 PM   #668
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hi 44250,
i checked all hfe from 2n tranies, but readings are different from one to one,
readings hfe's 187,195,198,180,176,200 like that.
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Old 5th November 2012, 07:12 PM   #669
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at least create a group of closest possible,say two 2N5551 of 193 and 190, with two 2N5401 of 189 and 192. second groupe could be for two 2N5551 of 173 and 170 with two 2N5401 of 169 and 172. First group would go to one chanel and second group in another chanel. be aware also that pcb is designed for 2SAxxx and 2SCxxx transistors that have different pinout. BC3xx also have different pinout compared to BC6xx -so you must check ALL transistor pinouts with scheme and apply it on pcb. i have done that and it worked from its first time.
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Old 12th November 2012, 06:01 PM   #670
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Hello.
This amplifier can be powered from a +/-93v supply?
Thanks.
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