Re: Pioneer receiver model SX636 amplifier bias question
- From: "Mark D. Zacharias" <spammenot@xxxxxxxxxxxx>
- Date: Thu, 16 Mar 2006 01:44:52 GMT
<captainvideo462002@xxxxxxxxx> wrote in message
news:1142445107.874278.126800@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I replaced two noisey intermittent preamp transistors in one channel of
this unit with NTE324's. These are supposed to be a direct replacement
for the originals. The unit seems to work well. All transistors in both
channels under quiescent conditions seem to run cool enough and there
is no noticeable distortion when driving the amps at sufficient volume.
However I have noticed that after a few minutes at sustained loud
volume the complementary output transistors on the repaired channel
seem to be running noticeably warmer than the other. They are nowhere
near "alarmingly" warm but just enough to let me know that there is a
difference. I have taken some comparative voltage measurements between
both channels and as expected have noted some differences. I have
attempted to tweak the bias pot on the repaired channel to even things
out between the two channels but it seemes like for instance if I
adjust the pot so that the emitter on one of the outputs matches the
same transistor on the the other channel it throws sonmething else off.
Should I just go for 0volts at the midpoint of the two outputs at the
big inductor or might there be more to it than that? Without the
service manual I don't know where to make the measuremenrt or what to
adjust it for. This appears to be a direct coupled amp with 4A fuses to
the speakers and without a capacitor on the output. I've seen
amplifiers of this type destroy speakers before so I don't want to make
a mistake with this. Can anyone advise me further. Thanks for any
assistance. Lenny Stein, Barlen Electronics.
Measure across the emitter resistors with no load. Adjust for the same as
the other channel. If the heating difference re-appears with a load, there's
a dc offset, maybe a small one but it can make a difference in effective
bias.
Mark Z.
.
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- Pioneer receiver model SX636 amplifier bias question
- From: captainvideo462002@xxxxxxxxx
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