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Karl vd Berg 4th January 2013 02:28 PM

Grounding a vintage amplifier
 
2 Attachment(s)
Hi folks,

Maybe this was already discussed, but I couldn't find the proper place.

I'd like to ask if can change safely my Sansui AU-317's power cord to a more robust grounded one.

The "original" (2nd picture) is not that robust anymore and I'm afraid it will break in the case sometime.

I want to put a 250V 10A with the yellow wire (1st picture) and ground it at the amp's chassis.

Is there anything I have to avoid with the AU-317??

jaycee 4th January 2013 04:38 PM

Make sure the signal ground is not connected to the chassis, otherwise you will probably get hum. Simply measure for conductivity between the case and the outer edge of one of the signal input sockets.

If there is a connection, you are best leaving the safety ground disconnected, but you can still fit an IEC socket which would allow you to use an IEC cable.

Karl vd Berg 4th January 2013 05:08 PM

Quote:

Originally Posted by jaycee (Post 3311033)
Make sure the signal ground is not connected to the chassis, otherwise you will probably get hum. Simply measure for conductivity between the case and the outer edge of one of the signal input sockets.

If there is a connection, you are best leaving the safety ground disconnected, but you can still fit an IEC socket which would allow you to use an IEC cable.

Excellent! So, if there isn't any conductivity between the case and both of the input socket (with gear switched on), it's safe to ground in the chassis, right?

And remember the Rotel? I followed your instructions and put another transformer, did the Bias adjust (totally out of specs!) and now it's sounds really nice!:) The other transformer didn't have any thermal fuse inside, so I had to change the transformer!

jaycee 5th January 2013 12:41 AM

You can test it while it's not switched on. Just use an ohm meter or so. A lot of Japanese amps did not have grounded cases.

Good news about the Rotel. They do have thermal fuses in the transformers but they are buried right inside the windings, so there's no chance of replacing them. Glad to hear the substitute works well. I have an RA-930 AX myself, a bit battered (the plastic base cracked and someone took out the rubber end cheeks) but it has a nice sound.

east electronics 5th January 2013 02:44 PM

Quote:

Originally Posted by Karl vd Berg (Post 3311085)
Excellent! So, if there isn't any conductivity between the case and both of the input socket (with gear switched on), it's safe to ground in the chassis, right?

And remember the Rotel? I followed your instructions and put another transformer, did the Bias adjust (totally out of specs!) and now it's sounds really nice!:) The other transformer didn't have any thermal fuse inside, so I had to change the transformer!


(totally out of specs!)

expected ...wonder why ? i think there is a bias stabilizer cap that goes bad ....if you also talk about the stupid yellow capacitor in the feedback of 100ufd/6.3 Volt is also joke quality and specs

it will be much better to replace those ...

Karl vd Berg 6th January 2013 03:22 AM

2 Attachment(s)
Quote:

Originally Posted by sakis (Post 3312122)
(totally out of specs!)

expected ...wonder why ? i think there is a bias stabilizer cap that goes bad ....if you also talk about the stupid yellow capacitor in the feedback of 100ufd/6.3 Volt is also joke quality and specs

it will be much better to replace those ...

Hello Sakis!

Yes! the bias was out a lot! Has to be 4mV and the right chnl. was 5.8mV, while the left chnl. was 38mV!

You might be right. Do you mean those tiny yellow/orange caps near the input source?? They are the only ones in that color, the others are Black Gate (the amp is from 1994 though!)

If those yellow are behind the bias stabilizer, I can put some Panasonics FC I still have... :)

east electronics 6th January 2013 12:57 PM

from 4 to 5.8 is no problem but 38 might be it seems that your amplifier doesnt use this typos of caps so you might as well be ok

the cap can be seen as the last cap to see in your phono stage right middle top side of your picture ...usually these are the caps that go bad ...

your version seems upgraded so nothing to be bothered


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