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Paulo
Reply with quote  #1 
Hi,
Can anybody help me about original power tubes on the Au-70?
In the schematic I found 7189 and in the service manual 7189A.
What is the correct part?
Thanks
Paulo
Isao Asakura
Reply with quote  #2 
Hello,

The differences between 7189 and 7189A are

7189's max screen grid voltage is 330V vs 400V of 7189A.  Also, pin 1 of 7189A is internally connected to pin2 (control grid), and pin6 of 7189A is internally connected to pin 9 (screen grid).   

Since AU-70's screen grid voltage should be 315V, 7189 might be adequate.  however, if your primary is 127V (like mine) instead of 117V, your screen grid might be running at much higher than 315V.  So, I would recommend to use 7189A rather than 7189.

Isao    
Paulo
Reply with quote  #3 
Hi Isao,
Thanks for your reply (help). When you say primary are we talking about inlet power transformer?

Paulo
Isao Asakura
Reply with quote  #4 
Hi,

I'm talking about the primary voltage of power transformer - should be equal to AC outlet voltage in your house.  It's supposed to be 120V in the US, but hardly ever.  European countries use 220V or 240V.

Isao
Paulo
Reply with quote  #5 
Hi again Isao,

I have 220V ac inlet, but I'm not sure if I understood your point of view. Independetly of ac inlet, AC power transformer gives you the correct voltage in the secundary for the main circuit, so you will have always the same voltage in the grid and plate of tubes.
Thanks
Paulo
Isao Asakura
Reply with quote  #6 
Sorry to inform you, but it's not correct.  If your primary voltage on your power transformer goes up, the secondary will be higher as well.  So, in my case, our house AC outlet measures 127V instead of 117V.  This 10V difference on primary will yield about 30 to 40V difference on the plate voltage.  Possibly, 20 to 30V difference on the screen grid.  

If your actual measurement of your AC outlet is 220V, you should not need to worry about this.  Your AU-70 should be set up with the 220V primary and you are all set.  You can use 7189 with no problem.

Isao    
Antonio
Reply with quote  #7 
Could one of you guys who is familiar with the AU-70 tell me what size fuse is supposed to be in it?  I replaced the tubes in mine, and blew the fuse after 45 minutes.  I don't know if it was even the correct one (bought used with no information and no tubes in it) and have since misplaced it....
Keeper
Reply with quote  #8 
Did you check the bias after installation of the tubes ?
If you check the service manual I believe all information you need will be found there.

If you need a service manual, operating manual
or other kind of literatures for Sansui and can't find a free copy I guess this is a very good good alternative.

http://www.obsinc.us/Dep_VOVS_Literatures.htm
Not free but very high quality. You can magnify several 100% for easy reading or print.

Free copies on the internet used to be blurred and hard to read

Click on any category and then do a search for the model and see what's available

Just a tip
Antonio
Reply with quote  #9 
You know what stinks?  I own the receiver, and the manual.  Neither is stamped with what the fuse should be.  I don't want to buy anything, and am hoping somebody who owns one can just verify the size.

I found a free manual for my AU-777.... I guess it's just hit or miss, with "free".

Thanks for the tips!  Hopefully I'll hear from someone who owns one/knows soon.  I think it's 3amp, but am not quite sure...

Keeper
Reply with quote  #10 
Quote:
Originally Posted by Antonio
You know what stinks?  I own the receiver, and the manual.  Neither is stamped with what the fuse should be.  I don't want to buy anything, and am hoping somebody who owns one can just verify the size.<br><br>I found a free manual for my AU-777.... I guess it's just hit or miss, with "free".<br><br>Thanks for the tips!  Hopefully I'll hear from someone who owns one/knows soon.  I think it's 3amp, but am not quite sure...<br><br>
I found a dirty manual and if you have the manual as you say you can see both in description and schematic it should be 3A main fuse.
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