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albedo039
Reply with quote  #1 
Greetings

I own a Sansui AU 111 and it appears that it still has the original tubes. My tech suggested that I should get new tubes but I am not shure what to look for. Okay, the tubes should be matched, but what else should be taken into consideration? Thanks in advance!

albedo039
Isao Asakura
Reply with quote  #2 

Hi,

 

You can find new 12AX7, 12BH7A, and 6L6-GC relatively easy.  But, you need to search harder for 6AQ8.  I have seen new ones on eBay before, but not regular bases.  You should be able to find used or NOS ones on Internet based tube stores. 

 

From my experience, original 12AX7, 12BH7A, and 6AQ8 tend to be still OK, but 6L6-GC's are usually worn out.  You can find NOS RCA 6L6-GC on eBay, but they are quite expensive.  If you want to use new ones, I recommend 6L6-GC's from JJ or EH.   

 

Before you fire your AU-111 up, I recommend to replace all coupling caps and 30uF 6WV cathode caps.  I also recommend to replace two 0.005uF on rectifiers.

 

Best,

 

Isao

 

Randall
Reply with quote  #3 
Hi Isao,

I have an AU-111 i'm trying to resurect. I am planning to follow your advice so I opened it up and noticed that someone alerady replaced the .3 output stage coupling caps with larger .68 caps. Will those be OK? It also looks like they removed all the 6uf 50v cathode caps from the entire amp. Should i put them back? Thanks for your help.

-Randy
Isao Asakura
Reply with quote  #4 

Hi Randy,

 

You should change the coupling caps back to 0.3uF.  Also, those cathode caps are for cathode signal path to stabilize the self bias voltage on cathode resistors, so you need to have them back.

 

Regards,

 

Isao   

Randall
Reply with quote  #5 
Isao,

Thanks for your help. I will add the 6uf caps and change the coupling caps back. (why would someone change the coupling caps to .68 to begin with? does it change the sound?) Do you recommend replacing all the suzuki oil caps in the amp? Also should i change all the coupling caps? There are a lot! Also what would you recommend for rectifier replacements? 1N5408's? Someone told me they thought that 1N4007 wouldn't be enough because of the voltage doubler. Thanks.


-Randy
Isao Asakura
Reply with quote  #6 

Hi Randy,

 

Higher values of coupling caps are supposed to improve the low frequency characteristics.  Well, you can do that on non NFB amps with little considerations.  However, the AU-111 applies the global NFB within the power amp section.  If this is a case, the combination of coupling caps (in each amplification stage) under the global NFB need to be maintained with the certain values - otherwise, the phase in low frequency will be shifted at the end.  This is the reason why you need to use the 0.3uF coupling cap.

 

Yes, IN4007 would be OK, but of course, you can use IN5408 as well.  If you like experimentation, try Fast Recovery diodes instead.  You might be able to notice the differences in sound - somewhat crispier.  Some people might like it, some might not. 

 

Sincerely,

 

Isao   

Randall
Reply with quote  #7 
Isao,

I did some searching online tonight but could not find 6uf 50v caps. Any recommendations on which brand and where to get them? Thanks again.

-Randy
Isao Asakura
Reply with quote  #8 

Hi Randy,

 

6uF, 50V caps???

 

Which cap are you working on?

 

Isao

Randall
Reply with quote  #9 
Sorry, I got it backwards. They are 30uf, 6V caps.

-Randy
Isao Asakura
Reply with quote  #10 

Hi Randy,

 

You can find those caps on http://www.mouser.com  Nichicon is a good brand.

 

I remember that one of well known amp designers said not to use cathode caps which are too much of over voltage capacity.  This means pick cathode caps like 30uF 6-25V, not like 30uF 50-100V.  He said large voltage capacity cathode caps don't sound good.

 

Regards,

 

Isao     

Randall
Reply with quote  #11 
Hi Isao,

Well its been a while and i'm finally ready to get back to work on my Sansui AU-111. I never did order those caps previously, so I was looking online to order them today and have been unable to find a 30uf 6v cap by nichicon. The only type I could find are tantalum foil caps by Kemet and they are very expensive. Any help finding the correct ones would be greatly appreciated. Thanks again.

-Randy



 http://www.mouser.com/search/ProductDetail.aspx?R=T197A306K006ASvirtualkey64600000virtualkey80-T197A306K006

Family_Dog
Reply with quote  #12 
Randy,

See my reply in the other AU-III thread.

-Eric

richard
Reply with quote  #13 
as we know the AU-111 pre-amp part using Five   ''12ax7 '',
but is any one know which '' 12ax7 '' ( they have 5 ) is using on AUX part ?????

rock
Reply with quote  #14 
My AU 111 needed new 6L6 GC week ago.

I adjusted the bias to read -44 vdc?Not sure if this was OK.

For your info0rmation,This unit was repaired before i got it years ago.

I noticed that right chanel is lower in amplification but still continue listenning to this amp despite.

Further checked when perorming power tube replacement,found volume control is 250 K Ohm B where the balance control is probably still original 250 K Ohm B.

The circuit diagram given 500 K Ohm B for the volume control.

Could this cause channel imbalance?

Your guidance would be highly appreciated.

Brgds,

Pks
Bud Rian
Reply with quote  #15 
I bought AU111 3 years ago but without top cage. I would be grateful if you could recommend, where to buy it. Thank you
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