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Old 30th April 2007, 11:37 AM   #1061
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Default Yes..i was distant from computers..i could not track forum

Your adjustment steps are fine Nordic..also the "special reduced current biasing", to find 50 miliamps is interesting too.

The off set multimeter will be there, connected into the output line, reading DC milivolts, only during those adjustments.... all multimeters must be removed, also the protective rail resistances must be removed after you finish bias and off set adjustment.

Remember to remove the input short you have made in advance to play the amplifier.

The standard biasing is 800 to 1100 milivolts measured over 10 ohms resistance.....but your heatsinks are not so enormous as we have dreamed.... a smaller current, when iddle, can be helpfull to maintain your temperature stable.

Are you using bias resistances?...or using diodes or VBE multiplier.

Before power the amplifier, i suppose you have measured resistance from plus to ground...from negative rail to ground...from positive to negative....and all those measurements made once more, but this time with ohmeter probe points inverted in polarity referenced the first measurements made. All
reading must be high...something over 30K....this will show you that no short is present into the board construction.

Before you remove your protective pillow (ahahahah) check for possible electrolitic condenser polarity inversion...and also check once more if they are 35 volts or much more related working voltage.

Beeing carefull this way...for sure you will not have surprises...well...are you sure the positive wire is really positive?
hehe....i happens dear Nordic....more often than you can imagine.

regards,

Carlos

.................................................. .................................................. ...

Greg

The standard biasing procedure, published in our home page, is correct.

The small reduction was "arranged" as i could see Nordic draws about the amplifier case, the enclosure...depending the way he will arrange the heatsinks..if fins in vertical or horizontal position, he will have reduced heatsink performance...also if he install some cover...something covering and creating problems to convection, the heat transfer to the air will be worst than we have imagined before.

I suggested to Nordic, to bias into a very small biasing point...and i hope he will not listen this amplifier with headphones using 100 miliwatts of power only...as under this power the biasing will be critical and some distortions in very low level signals may happens....the 80 to 100 miliamps biasing is much more safe..but iddle heat is bigger.....7 watts to the standard biasing...and 3 to 3.5 watts with stand by bias reduced.

Nordic environment is hot, as he told us...this turns things a little bit more problematic to heatsinking.

regards,

Carlos
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Old 30th April 2007, 12:07 PM   #1062
Nordic is offline Nordic  South Africa
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DC rails with baby transformer reading 31.6v.

Now going to drain voltages and solder in resistors' other leg to procede...
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Old 30th April 2007, 12:32 PM   #1063
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baah something is wrong

The 240v 60W bulb lit up to show innitial surge, then dimmed for about 4 seconds and lit right back up...

now it shows 10.3v over positive rail resistor and almost no voltage over negative...

Nothing smoked, burned or got hot due to current limit of bulb....
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Old 30th April 2007, 01:09 PM   #1064
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Default For sure, there are errors in the construction.


Base inverted related emitter....check circuit till you discover..do not give up, as there are errors.

It is normal to check, also double check, and not to observe that assembled transistors in the wrong way.

I have made that more than hundred times...
as i have constructed many amplifiers....experience do not make you better than others....the difference is that you will insist,beeing sure, that human errors are normal.

Please inform, once again, the transistors you are using....BC640 is a hell complicated, as i could find two different diagrams of leads in two different factories.

regards,

Carlos
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Old 30th April 2007, 01:31 PM   #1065
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Default Observe that some brands have different pin conections

If you are using one of those ones, better to check the base with our Multimeter.

Diode position...the base will be the one that will conduct to other leads.....and also will not conduct if you invert probe point polarity.

regards,

Carlos
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Old 30th April 2007, 01:32 PM   #1066
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Default Observe diagram, as invertion exists

regards,

Carlos
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Old 30th April 2007, 01:35 PM   #1067
Nordic is offline Nordic  South Africa
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I could fit bc640 pins in multimeter, it was ECB
Useing tip41 and tip42 BCE ????
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Old 30th April 2007, 01:37 PM   #1068
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Default Observe the detail...this confuses a lot.

regards,

Carlos
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Old 30th April 2007, 01:40 PM   #1069
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Default Check all them Nordic....a good idea is to remove and measure them outside the board.

Test the voltage amplifier one, and the output too.

Them check all resistances values.

Do not stop till you find an error..because for sure an error exist.

regards,

Carlos
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Old 30th April 2007, 01:46 PM   #1070
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for sure, poitive rail to ground measures only 12 ohm...!!!!!!!!
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