Sansui 2000 output transistor mismatch

[Dom123]

Hello AK'ers,

While revelling in mu AU-G90X, I needed a new project to fiddle with, so I just picked up a Sansui 2000 for the price of a couple of packets of cigs. It was saved at the last minute from a landfill and to the uninitiated looks a pile of junk. Surprisingly heavy.

It's in a sad state, but all knobs are there. The main issue is rust on the inside and a thick coating of a nasty sticky/oily layer all over the inside which I guess is tar/nicotine, and the plastic plexi outer front screen is missing. It looks to have been sitting in a damp environment for several decades... The outer cover is scratched and rough but a respray should sort that

Anyway I plugged it in via the DBT, which shone brightly, but then after 10 secs or so started to dim until fully out.
Wthout going into details, copious amounts of deoxit later, it produces music both channels. Doesn't sound too bad.
So the plan is to change all e-caps & replace all 2SC458 transistors. Several caps looked charred & have shrunken wrapping.

I've changed the electroylic caps on both power amp boards and on the power supply, as well as the 2SC458's on these board . These caps were gone ! Typically double reading of norminal value or even tripple for the 33uf ones !

The issue is that the output power transitors are wrong. One channel is a pair of 2SC1079, and the other channel a pair of 2SC889. Not good news. This looks to have been done many years ago.
The originals should be 2SC493, but according to AI, it says this is a misprint in the Sansui manual and they should be Toshiba 2SC793 ! I'm dubious about this.

So I think the best bet is to replace the output transistors before proceeding much further. I've read that Onsemi MJ15003's are a good sub. These are currently avialable at Reichelt for 7Euros each.
Can anyone confirm this is the most suitable sub, or is there something better ?

Also finally, is it worth investing much in this amplifier which must be 55 years old ? How would it sound compared for example to an AU-555A or a slightly later generation reciever such as a 661 for example ?

 

[petehall347]

which exact model is it ? if its 2000x outputs are 2SC793 or 2sd202 if its 2000a then 2sd202 the 2000 2sc493 according to the schematic

 

[Dom123]

It's the 2000, original model. I read that MJ15003 can be used as a replacement.

 

[Dom123]

I have left the two sc1079's on one channel, and fitted two 2S2793 that I happen to have lying around from a previous project. This is temporary measure. Both have higher specs than the original 2SC493 it should have.

I have just finished recapping the whole amplifier and swapping out all 2SC458. New bulbs everywhere.

What a pain to work on ! Solder wick was pretty useless. I have never come across an amp where the small caps were so out of spec, reading more than double original capacitance is most cases !

She sounds pretty good on some speakers in the garage. Equal volume both channels. I haven't adjusted the amp but centre voltage in balanced both channels. The tuner is excellent, great reception.

Feeling good about this project as this was one ratty and rusty amp saved from its final trip to the dump

There are a few issues though :
1) The volume gets loud very quickly, really limiting the effective use of the volume potentiometer
2) The sound is too bright for my liking, but I guess the tone controls are there for that. Reminds me of a 555a I restored

I guess the unbalanced output transistors would be changed.

 

[Dom123]

Been running the amp on my main system and frankly most of my previous comments aren't really justified.

This amp sounds phenomenal, really taken a back. I was running a marantz 1060 just before swapping over, which in itself is a another great sounding amp, but the 2000 just sounds better in all respects. The sound is so lush with deep bass, maybe not so sharp but really enjoyable. The highs are good with good detail also but definitely not over bearing or tiring. The good thing is that the background is really silent. 100% a keeper amp !

This is strange because I didn't like so much the AU-555A (of which I have had 4) and the sound is definitely more involving than my pristine restored AU-777.

This hobby is full of surprises. Next stop back to my AU-G90X, which hopefully will put things back into perspective.

 

[ConradH]

Sansui used at least three different outputs and I don't think the circuit is terribly fussy. Just be sure the voltage and current specs are sufficient. I also don't think matching is terribly critical, though I do at least test them and aim for close.

 

[Dom123]

Thanks for the response. Both pairs of outputs have higher specs than 2sC458.

Good thing is I can't detect any difference in sound output and sound quality between both channels, and the amp is drawing very little current and runs cool. I'm not sure to change the outputs now as this thing sounds so enjoyable.