Sansui AU70 thoughts

[Sloper1940]

Goodaye all

First bit of help l need is to stop buying Sansui amps.
Second l just got a Sansui AU70 amp, very neat original condition.
Working but a little distortion in one channel.

My plan is to first clean it and replace the oil and electrolytic caps.
Any suggestions on type of film caps to replace the oil?

Should l replace the diodes as well?

l will check all the resisters are in spec.
Are there any problems or traps in these things?
And yes l will discharge the big caps before l start.



regards Bruce

 

[smurfer77]

Hi, congrats on your purchase. The AU-70 may be a bit of a rat's nest inside but it's truly one of the best amps I've ever heard.

First thing to do is replace all of the coupling caps, which is currently being handled by oil caps you have mentioned. Those can be replaced by polypro or polyester film caps. Any respectable brand will sound just fine. I prefer to use axial instead of radial caps for that, to make life easier and make the job look neater. It's not a bad idea to go up a little in voltage rating, but keep capacitance value as close as you can, unless you really know your schematics.

Here you can see my AU-70.

Diodes are somewhat optional. My recommendation is to replace them though... I had one go faulty in my TU-70.

Double check all of the plate resistors.

I'm told the cathode caps all need replacing (you will see each tube has a little electrolytics from cathode of tube to ground). I had no problems with mine but replaced them anyway.

I've had a lot of leaking brown dominoes caps (mica). So I replaced all of those too although people often say they are okay to leave alone.... i've found many bad ones in my gear from this era.

As for your specific problem, any chance it's a tube? tried swapping tubes around and seeing if channel changes? I assume you've fiddled knobs and switches a lot to see if it's related to dirty switches......but worth double checking that too

 

[Sloper1940]

Goodaye

This is the first tube amp or device l have ever owned,
l have fixed a number of SS Sansui amps and although l have a piece of paper saying l am trained, did a lot of digital stuff.
Relearning analouge has been slow and interesting.

Valve stuff, no idea.
So l am working on the KISS principle, do what l know, capacitors, diodes and cleaning.
l have a good repair shop which l will take it to, to adjust it and check it over when l am finished.

Not using it until its capped, but everything works so thats a good start.

l had read your thread a few times now and may need some help with the capacitor stuffing, pinouts and such.
But in saying that l was also thinking of hiding the new coupling caps underneath.
The only time l struck multi capacitence was with motor starting.

Also in the AU505's and AU555's l own l have cascaded the coupling capacitors lowering the noise floor and improving detail.
Can it be done in this amp?

My birthday is coming maybe the kids will get me new tubes.

PS one of my cars used to drive the roads of Calafornia.

regards Bruce

 

[smurfer77]

Goodaye

This is the first tube amp or device l have ever owned,
l have fixed a number of SS Sansui amps and although l have a piece of paper saying l am trained, did a lot of digital stuff.
Relearning analouge has been slow and interesting.

Valve stuff, no idea.
So l am working on the KISS principle, do what l know, capacitors, diodes and cleaning.
l have a good repair shop which l will take it to, to adjust it and check it over when l am finished.

Not using it until its capped, but everything works so thats a good start.

l had read your thread a few times now and may need some help with the capacitor stuffing, pinouts and such.
But in saying that l was also thinking of hiding the new coupling caps underneath.
The only time l struck multi capacitence was with motor starting.

Also in the AU505's and AU555's l own l have cascaded the coupling capacitors lowering the noise floor and improving detail.
Can it be done in this amp?

My birthday is coming maybe the kids will get me new tubes.

PS one of my cars used to drive the roads of Calafornia.

regards Bruce

Unlike the 505/555A there will be little benefit from playing with the cap coupling values/strategy. Just use as close to original C and increase V.