To Recap - A Question

[Family_Dog]

I am in the process of replacing the coupling capacitors and electrolytics in a Sansui AU-111. Sansui was very adamant about using specific caps in their circuit, and reading through the various web sites I have found, special mention of this was made too.

I've never really bothered about this, how critical would this be? I realise some people state that there is a definite sound advantage to using the correct caps, e.g. oil caps for coupling purposes, but is this really so critical? I want to recap this amplifier but I don't want to kill the so-called "Sansui" sound.

What say those that knoweth?

[Geek]

Hi,

Some good reading:
http://members.aol.com/sbench102/caps.html

[Family_Dog]

Geek,

Brilliant reading, thank you very much!

[gingertube]

If the SANSUI is full of those "oil" coupling caps that "infested" 1970's Pioneer etc. Japanese equipment then you have a job ahead of you (caps often had a Toshiba brand name). I started to recap a Pioneer Amp by testing each of those caps and replacing those that were leaky. After having to replace 8 of the first 10 tested I just replaced the lot. I had similar experience with a "Star 30". In both cases leaky coupling caps to the output stage were causing output tubes to cook. When I looked at other parts of the circuit I did'nt consider going over the top with replacement caps to be worthwhile and so just used common 400V Polyester. There was'nt really room for anything better anyway (Polypropylenes to suit are about twice the size).

Anything is better than those "Oil" caps. NOTE: these are NOT paper in oils or any of that flash stuff you see referred to in power supply threads here - I'm not certain what their construction actually was BUT they were rubish and I can say that 80% + off them are now No Good.

Cheers,
Ian

[DigitalJunkie]

I've seen those caps labled "Suzuki" in amps.. physically,and electrically leaky! Replace them,quick.

[Family_Dog]

I tested the coupling caps with a LCR meter and found in all cases they exceeded the actual capacitance as marked on them. Admittedly, this is not the most ideal way of testing the caps, but it certainly does provide an indication as to their efficacy. None of the caps looked suspicious either, so I powered up with a Variac and soon the sweet Sansui sound was evident.

AFAIR, the original caps are marked "Elna", I'm at work now so can't verify this. However, even the electrolytic filter caps seem to be doing their job properly, there is no hum evident at all. Voltages all seem good, but I am still busy running through the circuit.

The Bias voltages on the 6L6GC seem fair at around 47-49v negative, and none of the valves are glowing cherry red, so things don't appear too bad.

I might still consider replacing the coupling caps as they are old and quite liable to fail under stress.

-Eric