Sansui 9090: Original, everything works. Should I change anything?

IME, with sansui, they will misbehave sooner or late until properly reconditioned.
My experience is the opposite. Of the four I have owned (QR-6500, QR-4500, 2000A, 9090) none have needed any maintenance other than Deoxit.
 
Just got a meter that measures ESR. I kept the e-caps I pulled from the driver board. Also had a spare of each of the replacements, so I tested those also for comparison. Here are the readings:

Spec: 80V, 100µF Reading: 110.5µF, ESR=0.13 ohm Replacement cap ESR=0.09 ohm
Spec: 80V, 100µF Reading: 110.0µF, ESR=0.15 ohm

Spec: 6.3V, 100µF Reading: 98.9µF, ESR=0.29 ohm Replacement cap ESR=0.41 ohm
Spec: 6.3V, 100µF Reading: 95.0µF, ESR=0.30 ohm

Spec: 50V, 0.47µF Reading: 0.446µF, ESR=9.5 ohm Replacement cap ESR= 4.4 ohm
Spec: 50V, 0.47µF Reading: 0.474µF, ESR=9.3 ohm

So, all caps were within 10% of spec for capacitance. ESR is very close on the larger caps, smaller ones were double of the new one. Just wanted to share the data. This fits the pattern I saw when only measuring capacitance of old caps - the smaller ones (< 10µF) are most likely to be out of spec. Is there an acceptable range for ESR on e-caps?
 
I'm with you OP, my experience has been very good without resorting to full recapping, which I think can alter the sound, and not always for the better.

Then again I purchase gear with long term ownership in mind, so generally stick to good condition, indoor-stored gear. Haven't had any problems. Often with good quality capacitors, every single cap on even 40-50 year old equipment will test within spec.
 
I'm with you OP, my experience has been very good without resorting to full recapping, which I think can alter the sound, and not always for the better.

Then again I purchase gear with long term ownership in mind, so generally stick to good condition, indoor-stored gear. Haven't had any problems. Often with good quality capacitors, every single cap on even 40-50 year old equipment will test within spec.

Electrolytic capacitors have a working service life, anything outside of that is borrowed time and they are in a state of degradation..
For a unit from 1976, the caps will not all measure in spec. Some will but a lot wont, in some cases caps will show good capacitance but this does not mean the cap is good, it can mean that the cap has high internal resistance for example, I am always weary of a 40 year old cap reading higher capacitance than specified.

Putting new, and higher quality caps that were not available at the time of manufacture will bring the unit back to factory spec, and in some cases better than.
At no time in the hundreds of recaps I have done for customers have I ever experienced a unit which sounds worse after a recap and updating of ageing leaky semiconductors.
In every case I have documented improved performance.

I hear and see people saying "the caps all tested good", and I assume with a hand held meter of some kind, little attention is given to how the caps perform at their working voltage, ESR and most importantly, Leakage.

Its a free world and people are entitled to follow your preferred path, but in these cases I think its worth going into it with information from both sides.

I like to say, "your amplifier did not leave the factory with 40-50year old caps in it, so in order to maintain performance and reliability, updating components at the end of their service life is essential."
 
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