DjLeco
Moderator
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.
[Youtube] https://www.youtube.com/watch?v=o8lNBT513I4&feature=youtu.be [/Youtube]
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.
[Youtube] https://www.youtube.com/watch?v=o8lNBT513I4&feature=youtu.be [/Youtube]