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Sansui AU-70 Tubes Replacement and Alternatives

mozcho

mozcho

Well-Known Member
I just bought a Sansui AU-70, my first tube amp, the manual says the tubes used are:

7189 x 4
12AX7 x 3
6AN8 x 2

I'd like to know, do we have to get the exact models for these three types of tubes, or there are equivalents? I ask because tubes are not common in my country, it'd be easier if equivalents exist.

A second question, do I need to use the same brand for these tubes, say, the 7189s must come from the same brand?

Thirdly, if I change any tubes, do I need to do the biasing? I don't know what is this, I'm not an electronic guy.
 
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mozcho said:
I just bought a Sansui AU-70, my first tube amp, the manual says the tubes used are:

7189 x 4
12AX7 x 3
6AN8 x 2

I'd like to know, do we have to get the exact models for these three types of tubes, or there are equivalents? I ask because tubes are not common in my country, it'd be easier if equivalents exist.

A second question, do I need to use the same brand for these tubes, say, the 7189s must come from the same brand?

Thirdly, if I change any tubes, do I need to do the biasing? I don't know what is this, I'm not an electronic guy.
Click to expand...

1. Lots of equivalents for the 12AX7, but this is the most common tube type so you won't have to look far to find one.

2. 7189 can be replaced by the Russian 6P14P.

3. 6AN8 no substitute I know of and no longer made, but this is a low demand tube now which was made in large quantities in the past, and should be easy to find.

4. Same brand of tube is not necessary, but the amp will perform best if they have matching electrical characteristics. If you don't know what this means just google tube matching, or matched pairs of tubes, etc.

5. If the 7189 tubes are changed, yes the bias must be adjusted. Bias is a negative voltage which controls how much current flows through the tube. Since tubes are all a little different than each other, this must be adjusted each time an output pair is replaced. The other tubes do not have or need adjustable bias.

6. If the amplifier has not had the electrolytic and paper capacitors replaced, this must be done before you can consider it reliable. The AU-70 output transformers are sensitive to over current conditions, and nearly impossible to replace, so do not use this amplifier until a competent person has replaced the relevant components and declared it to be in good health.

I think you will need to make a decision to either find a tech you can trust it with, or learn enough about electronics to do the work yourself. If you take the second path I do not suggest learning on the AU-70, as too much can go wrong, and it is not really the best platform for learning.
 
Great advice from maxhifi. One other thing: the Sovtek EL84M is a fine replacement for the 7189 as well and is widely available. In fact, I suspect that it is probably a branded version of the Russian 6P14P-EV.
 
maxhifi said:
1. Lots of equivalents for the 12AX7, but this is the most common tube type so you won't have to look far to find one.

2. 7189 can be replaced by the Russian 6P14P.

3. 6AN8 no substitute I know of and no longer made, but this is a low demand tube now which was made in large quantities in the past, and should be easy to find.

4. Same brand of tube is not necessary, but the amp will perform best if they have matching electrical characteristics. If you don't know what this means just google tube matching, or matched pairs of tubes, etc.

5. If the 7189 tubes are changed, yes the bias must be adjusted. Bias is a negative voltage which controls how much current flows through the tube. Since tubes are all a little different than each other, this must be adjusted each time an output pair is replaced. The other tubes do not have or need adjustable bias.

6. If the amplifier has not had the electrolytic and paper capacitors replaced, this must be done before you can consider it reliable. The AU-70 output transformers are sensitive to over current conditions, and nearly impossible to replace, so do not use this amplifier until a competent person has replaced the relevant components and declared it to be in good health.

I think you will need to make a decision to either find a tech you can trust it with, or learn enough about electronics to do the work yourself. If you take the second path I do not suggest learning on the AU-70, as too much can go wrong, and it is not really the best platform for learning.
Click to expand...
Thank you for the valuable advice!
 
Dave451 said:
Great advice from maxhifi. One other thing: the Sovtek EL84M is a fine replacement for the 7189 as well and is widely available. In fact, I suspect that it is probably a branded version of the Russian 6P14P-EV.
Click to expand...
I read this:

"The afforementioned 6p14p is an equivelent, and the 6p14p EV is the 7189A equivelent. Do not mix the regular and A/EV versions." - https://audiokarma.org/forums/index.php?threads/7189-power-tube-alternatives.367075/

I'm a little confused.
 
mozcho said:
I read this:

"The afforementioned 6p14p is an equivelent, and the 6p14p EV is the 7189A equivelent. Do not mix the regular and A/EV versions." - https://audiokarma.org/forums/index.php?threads/7189-power-tube-alternatives.367075/

I'm a little confused.
Click to expand...

The 6P14P was the tube made for the Soviet proletariat, used in radios, phonographs and televisions of the 1960s and 1970s. It is a cheap mass produced tube.

The 6P14P -EV is a similar tube but was made to a higher standard than the ordinary 6P14P, and therefore can tolerate the conditions the 7189 is used at a little better. I agree with Dave that is best to use the EV version in your application as it will live longer and not create problems.

To be frank, it it were my own personal Sansui, I would seek out a quad of NOS 7189A tubes, but the Russian tubes do present a lower cost option.
 
maxhifi said:
The 6P14P was the tube made for the Soviet proletariat, used in radios, phonographs and televisions of the 1960s and 1970s. It is a cheap mass produced tube.

The 6P14P -EV is a similar tube but was made to a higher standard than the ordinary 6P14P, and therefore can tolerate the conditions the 7189 is used at a little better. I agree with Dave that is best to use the EV version in your application as it will live longer and not create problems.

To be frank, it it were my own personal Sansui, I would seek out a quad of NOS 7189A tubes, but the Russian tubes do present a lower cost option.
Click to expand...
I see, so 7189A (and 6P14P-EV) are usable on AU-70, not 6P14P? I'll take note of that.

If I need to buy from the bay, are there any reputable sellers that can be recommended? Or maybe I should join BT here and buy from members?
 
The Sovtek EL84M is a currently produced version of the 6P14P-EV. Made in the same factory. You may find them to be more available and better matched. I have bought the old Soviet tubes and gotten ones that are extremely mismatched.
 
mozcho said:
I read this:

"The afforementioned 6p14p is an equivelent, and the 6p14p EV is the 7189A equivelent. Do not mix the regular and A/EV versions." - https://audiokarma.org/forums/index.php?threads/7189-power-tube-alternatives.367075/

I'm a little confused.
Click to expand...

The advice is due to some changes to the pin connections.
https://audiokarma.org/forums/index.php?threads/7189-vs-7189a.668252/

http://www.bustedgear.com/res_Tube_...89A power pentode is,tube element, or to none.
Regards,
 
The 6P14P-EV will work. They are what I ended up using in the Sansui 500a, which required 7189a's. I did 2 different quads to get enough for current match. But are cheap enough no big deal. Pinout tie point as to @analogadict @larryderouin mentions above most likely needed. As 7189A are terribly expensive, even if you find a "matched" quad. Big fat chance they won't pull equal current.
 
mozcho said:
I just bought a Sansui AU-70, my first tube amp,

I'd like to know, do we have to get the exact models for these three types of tubes, or there are equivalents? I ask because tubes are not common in my country, it'd be easier if equivalents exist.

A second question, do I need to use the same brand for these tubes, say, the 7189s must come from the same brand?
Click to expand...

Did the Sansui come with tubes? if so why are you looking to replace them all?
 
Also anyone suggesting tubes and where to purchase them factor in that the OP is in Kuala Lumpur, Malaysia.

I'm not sure what the markets are like there price wise or if he/she would be better served purchasing in the larger Asia market which is closer.
 
Dswankey said:
Did the Sansui come with tubes? if so why are you looking to replace them all?
Click to expand...
I just bought it last week from a nice guy, everything was in good order originally. I worked wonderfully in my house when I brought it back. Two days later I changed to connect them to another pair of speakers, and here caused the trouble: the speaker connectors are not in banana plugs but in stock form (in fact the whole AU-70 is, he is the first owner from 1969, and he did not mod it except for tube replacement), after I screwed in the cables, and turned the amp 90 degrees clock-wise so that the front is facing toward me (my space is small and I can't move to the back of my rack to perform this), one of the cables for the right side just came off but I didn't realize it. I turned on the system and let it warm up for 5 minutes and started using it, then only I realized that the right side has no sound, and a visual check with a mirror revealed that one cable was off the terminal. I immediately power it off, wait for 30 minutes, then reconnect all cable securely. The second time when I power it on, I could hear the hum from the speakers. I took off the two output tubes and tried again, this time there was no hum at all coming from the left speaker. So I think the two 7189s for the right side is damaged, hence. I asked the seller but he did not keep any extra tubes, in fact, he is downsizing due to age, and he has sold his only tube amp to me,
 
mozcho said:
I just bought it last week from a nice guy, everything was in good order originally. I worked wonderfully in my house when I brought it back. Two days later I changed to connect them to another pair of speakers, and here caused the trouble: the speaker connectors are not in banana plugs but in stock form (in fact the whole AU-70 is, he is the first owner from 1969, and he did not mod it except for tube replacement), after I screwed in the cables, and turned the amp 90 degrees clock-wise so that the front is facing toward me (my space is small and I can't move to the back of my rack to perform this), one of the cables for the right side just came off but I didn't realize it. I turned on the system and let it warm up for 5 minutes and started using it, then only I realized that the right side has no sound, and a visual check with a mirror revealed that one cable was off the terminal. I immediately power it off, wait for 30 minutes, then reconnect all cable securely. The second time when I power it on, I could hear the hum from the speakers. I took off the two output tubes and tried again, this time there was no hum at all coming from the left speaker. So I think the two 7189s for the right side is damaged,
Click to expand...

Okay, however I don't think what happened would affect the 12AX7's and I could be wrong or the 6AN8's.

Curious how accessible are tubes in your country?
 
Dswankey said:
Okay, however I don't think what happened would affect the 12AX7's and I could be wrong or the 6AN8's.

Curious how accessible are tubes in your country?
Click to expand...
I am new in tubes so don't have a clear picture yet. There are audiophiles around in this country, a small fraction of them have tube amps. How big is the market—I don't know yet, but my rough estimation is that for a country of 30 million population, the decent audio equipment market might be smaller than 10% of New York City's. The biggest three cities here might have some shops that sell tubes, but I know many audiophiles and repairers here source their parts from the internet. The seller of the AU-70 has given me a shop in downtown, I wish to visit within these two weeks.

I really envy those who are in the US and Canada, where wonder deals often are reported, and many models and rare parts are much more accessible with prices that are more realistic too! I can't even get DeOxit here, have to buy from Amazon, and some sellers don't even want to ship it here.
 
mozcho said:
I am new in tubes so don't have a clear picture yet.... The seller of the AU-70 has given me a shop in downtown, I wish to visit within these two weeks.
Click to expand...

This is good new for someone who is new to tubes, I suggest before you purchase any new tubes visit this shop and explain what happened. I'm sure they'll inspect the unit to see what might of caused your issues and ascertain if there was any damage, and more importantly test all the tubes.

A lot of times the tubes will test fine.

Sansui's of that era was known for their quality engineering and my guess is that your AU-70 is a nice unit so do the right thing and have it looked at by someone.

On another note their is a dedicated sub-forum here at AK "Exclusively Sansui" that has a lot of knowledgeable Sansui enthusiasts who provide great suggestions and ideas.

https://www.audiokarma.org/forums/index.php?forums/exclusively-sansui.39/
 
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mozcho said:
I just bought it last week from a nice guy, everything was in good order originally. I worked wonderfully in my house when I brought it back. Two days later I changed to connect them to another pair of speakers, and here caused the trouble: the speaker connectors are not in banana plugs but in stock form (in fact the whole AU-70 is, he is the first owner from 1969, and he did not mod it except for tube replacement), after I screwed in the cables, and turned the amp 90 degrees clock-wise so that the front is facing toward me (my space is small and I can't move to the back of my rack to perform this), one of the cables for the right side just came off but I didn't realize it. I turned on the system and let it warm up for 5 minutes and started using it, then only I realized that the right side has no sound, and a visual check with a mirror revealed that one cable was off the terminal. I immediately power it off, wait for 30 minutes, then reconnect all cable securely. The second time when I power it on, I could hear the hum from the speakers. I took off the two output tubes and tried again, this time there was no hum at all coming from the left speaker. So I think the two 7189s for the right side is damaged, hence. I asked the seller but he did not keep any extra tubes, in fact, he is downsizing due to age, and he has sold his only tube amp to me,
Click to expand...

This fault does not sound like bad tubes to me. Taking it to a tech is the correct course of action- good luck!
 
also inclined to agree it doesn't sound like a tube issue. If this has a phase reverse or a speaker selector switch, that might be the issue. Bad connections will make the channel seem dead.
 
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