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Old 6th April 2015, 12:45 PM   #1
patnat is offline patnat  France
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Join Date: Apr 2015
Default Quiescent current Nytech CA 252

Hello,
I am new to the forum, I'm Patrick, I live in France and I bought my first amplifier built in 1983, is a Nytech CA252.
I change all chemical capacitors, and I would like set the quiescent current and AC midpoint 252 and 602 on a CPA.
The rest of my equipment consists of a platinum REGA P3 / 24, a preamp SANSUI AU 555A, a 3.5 NAIM CD player and a pair of FOCAL speakers.
Thank you for your answers.
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Old 7th April 2015, 04:46 PM   #2
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According to the schematic I found on the web:

Bias: Connect multimeter across R117 and R118, i.e. between the bases of TR105 and TR106. Adjust RV102 for a reading of about 8 mV. (If unstable / hard to adjust, turn off amplifier, turn pot from end to end, return to original position, turn back on and try again.)
Note - recommended bias current is only 10 mA, which is very low, but these amplifiers don't have much to offer in terms of heatsinking and I wouldn't want to risk blowing it up.

Symmetry adjustment requires some sort of sine generator and more importantly a dummy load (what were these units rated for, 4 ohms?) and an oscilloscope. I assume you don't have this kind of equipment? I would recommend just turning RV101 from end to end a few times and returning it to where it was.

Note that RV101/102 may appreciate a bit of a cleaning.
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Old 7th April 2015, 05:48 PM   #3
patnat is offline patnat  France
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Join Date: Apr 2015
Quote:
Originally Posted by sgrossklass View Post
According to the schematic I found on the web:

Bias: Connect multimeter across R117 and R118, i.e. between the bases of TR105 and TR106. Adjust RV102 for a reading of about 8 mV. (If unstable / hard to adjust, turn off amplifier, turn pot from end to end, return to original position, turn back on and try again.)
Note - recommended bias current is only 10 mA, which is very low, but these amplifiers don't have much to offer in terms of heatsinking and I wouldn't want to risk blowing it up.

Symmetry adjustment requires some sort of sine generator and more importantly a dummy load (what were these units rated for, 4 ohms?) and an oscilloscope. I assume you don't have this kind of equipment? I would recommend just turning RV101 from end to end a few times and returning it to where it was.

Note that RV101/102 may appreciate a bit of a cleaning.
thank you very much, I try at the end of the week.
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