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Old 29th December 2014, 04:46 PM   #1
DjLeco is offline DjLeco  Romania
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Default Labgruppen LAB4000 TD class

I have repaired today one Labgruppen LAB4000 amplifier, TD class amplifier.

Is supplied at +/- 155Vdc, and the trouble was in low frequency classB part amplifier.

I have replaced all 10 pairs of MJL21193+MJL21194 trannies, with brand new ones, I replaced some 18kOhms/2W resistors with 4 W ones and some 15V zenner 0,5 W (faulty) with 1,3W ones, recalibrated the +/- 7,5Vdc window, and bias after, and go to tests, each channel separately on 4 ohms dummy load:

The amp is able to deliver 98-99Vrms continuously on 4 ohm, and 104Vrms at clipping threshold, couple tenth of seconds until thermal limiting occurs.

So 100Vrms on 4 ohms is ok for one old amplifier like that.

Now I listen it on speakers, the sound is neutral, flat, a little lazy on high spectrum (above 12kHz), but pleasent to the ears.
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Old 2nd January 2015, 07:40 AM   #2
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Very nice Leco, show the waveform at collectors also.
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Old 2nd January 2015, 04:59 PM   #3
DjLeco is offline DjLeco  Romania
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Unfortunately, the amp is back at work, canot make any other measurements...
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