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Audio and Video Talk
The Vintage Audio Section
Any amp geniuses here willing to give advice?
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<blockquote data-quote="Rick" data-source="post: 847079" data-attributes="member: 17143"><p>I got hold of a Technics SU-8088K that I'm trying to repair.</p><p></p><p>I really like it and would love to get it working but its becoming a bigger challenge than I could imagine. I have repaired many amps and generally have a decent understanding but the circuitry in this thing is confusing me me they are using things like 2 diodes in series in single packages all over the place as well. Also, made in 1979 most of the transistors used are now obsolete, I have had to substitute best I can spending many hours immersed in data sheets.</p><p></p><p>I have the preamp section working perfectly now, its just the power amp, biasing seems to be an issue, after shorting out and wasting 8 X MJ15003/4 I have learned one lesson at least to power up though a 100W light bulb.</p><p></p><p>Below is one channel, bias is way too high, all damaged components have been replaced I switch on and it goes almost straight into thermal runaway, could be oscillation but I cant see anything on the scope.</p><p></p><p>I'm looking at how to modify and lower the bias.</p><p></p><p><a href="https://postimg.cc/image/4ghqesaid/" target="_blank"><img src="https://s26.postimg.cc/pq5cpmqt5/SU-8088_K_One_Channel.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></a></p></blockquote><p></p>
[QUOTE="Rick, post: 847079, member: 17143"] I got hold of a Technics SU-8088K that I'm trying to repair. I really like it and would love to get it working but its becoming a bigger challenge than I could imagine. I have repaired many amps and generally have a decent understanding but the circuitry in this thing is confusing me me they are using things like 2 diodes in series in single packages all over the place as well. Also, made in 1979 most of the transistors used are now obsolete, I have had to substitute best I can spending many hours immersed in data sheets. I have the preamp section working perfectly now, its just the power amp, biasing seems to be an issue, after shorting out and wasting 8 X MJ15003/4 I have learned one lesson at least to power up though a 100W light bulb. Below is one channel, bias is way too high, all damaged components have been replaced I switch on and it goes almost straight into thermal runaway, could be oscillation but I cant see anything on the scope. I'm looking at how to modify and lower the bias. [url=https://postimg.cc/image/4ghqesaid/][IMG]https://s26.postimg.cc/pq5cpmqt5/SU-8088_K_One_Channel.jpg[/IMG][/url] [/QUOTE]
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Audio and Video Talk
The Vintage Audio Section
Any amp geniuses here willing to give advice?
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