2. analog
  3. 125078-1452

Bad NOS tubes...

I just want to put this out there...as much as I would not like to...my head says otherwise. Tube buyers beware!!!

On 3/7/16 I bought 6 NOS Mullard 12au7 4003 tubes for my preamp from a vender out of Minesing, Ontario Canada... under the store front name of ’mullard.com’ http://www.mullardtubes.com/Mullard-ECC82-12AU7-CV4003/?ID=0&ProductID=153 and ’ tube products.com’ http://www.tubeaudioproducts.com/Mullard-Brimar/ProductDetail.aspx?CatID=65&ProductID=153#

The owner is one Alfred Kayser. On his site/sites he states all of his tubes are tested and matched for best performance values. Well,I went ahead and ordered and received said tubes. After 2-3 months of use I started to hear unacceptable levels of noise from my speakers,you know, the dirty sound of that dreaded tube noise of a scratching, distorted, dirty volume pot type of noise,which totally infringes upon the music. I went ahead and called Alfred and asked him about it and he just responded there is "nothing he could do" for me. Hey,no problem,but he advertised full-up tested tubes. If it was only one bad tube,I could understand,I’m a realist...things happen.

But!!!

Long story short,I came to find out that four of the six tubes are defective and are not what I paid for. Two are fine. So the moral of this story is...When buying tubes,do not go the cheaper route,find and use a "reputable" tube vender and save yourself some time,money and aggravation. Of course I will never use this guy again for any of my audio needs... Hope this is of some help to the Audiogon membership.

aolmrd1241
tomcy6's avatar
tomcy6
2,598 posts
 

Add me to the list of those who can hear differences between tubes and who enjoy fine tuning the sound of their systems with old stock tubes.

aol, Talk to Kevin Deal at Upscale Audio. He is the importer of PrimaLuna amps and the expert on them. He also has a great selection of NOS and current production tubes that are priced from very reasonable  on up.

He can probably tell you if there is a possibility that the tubes that went bad on you were not right for your preamp or if you just got some bad tubes, as you suspect.

Before you talk with him give the stock tubes a good listen and decide what kind of change in sound you want to hear with a change of tubes. He will give you his honest opinion, even if it’s not what you want to hear, which causes people to rant about him on this forum from time to time.

Buying old stock tubes does have risk. You can minimize the risk by buying from an established seller with a good reputation. Don’t let your bad experience sour you on tubes. They can definitely improve the sound of your system, IMHO.

Here are some other good sellers:

Tubemonger

Vintage Tube Services

Jim McShane

Brent Jessee

tzh21y
1,654 posts
 
Talk to Andy bowman at vintage tube services.  He will take care of you.
lewm
13,243 posts
 
Guys, Here are the facts as I see them:
(1) The OP bought 12AU7s for a preamplifier that presumably uses 12AU7s, so there is no question that he bought the right tube type. In terms of operating parameters, all 12AU7s are alike. (The OP should report to us if he changed tube types, but he did not say that he did.)
(2) A tube that looks good on a tester can only be relied upon to have been good at that moment. Tubes can fail unexpectedly and prematurely, whether NOS or current manufacture, but the hooker here is that 4 out of 6 tubes appear to have gone bad in such a short time. That defies the law of averages for tube lifespan, when tubes are used within the recommended limiting parameters.
(3) For this reason, we suggested that the OP might want to check out the voltages in his preamplifier; one cause of such a catastrophe would be abuse of the tubes, for sure. They DID last for more than a month before showing signs of early death.
(4) Against this hypothesis, the OP also tells us that his set of OEM tubes, presumably also 12AU7s, are all working fine after many more hours of use in the very same preamplifier. Moreover, he re-installed the OEM tubes and they are sounding fine.
(5) So, if we want to exonerate the vendor, one more hypothesis remains tenable: Perhaps something went bad in the preamplifier subsequent to the installation of the new tubes, something that killed 4/6 of them prematurely. If this is so, then the OEM tubes ought to go bad too, after a while. To test this hypothesis, I advise the OP to continue listening with the OEM tube set for a month or two longer; see how that works. Some or all of them will fail as well, if the preamplifier has developed a power supply problem. (This could involve either the filament supply or the B+ supply.) OR, take the unit now to a good technician for a check-up.

Peace. Out.
jea48
4,486 posts
 


aolmrd1241 said:

"After 2-3 months of use I started to hear unacceptable levels of noise from my speakers,you know, the dirty sound of that dreaded tube noise of a scratching, distorted, dirty volume pot type of noise,which totally infringes upon the music. "

~~

As someone earlier said the tube pins could be dirty. I would clean the tube pins with Isopropyl Alcohol. Then try them again.

I would like to know how the OP was able to determine all 4 tubes are defective.

I would suggest he find someone in his area to check the tubes.

I can't imagine buying vintage tubes and not owning a tube tester.

~~ 

The OP said he reinstalled 4 of the original tubes that came with the amp and the amp sounds fine again. I wonder if he then pulled one of the good tubes and then installed one of the bad tubes in it's place and then took a listen? (After cleaning the tube pins first).... If that tube did sound bad then pull it and try another supposedly bad tube and then listen to it again. Repeat the process until he has gone through all 4 tubes.

(Note: I don't know if this amp requires closely matched pairs of driver tubes. Or  closely match sections of each driver tube.)

~~

To the OP. I suggest you send an email to the tube vender you bought the tubes from with a Link to this thread. I think it's only fair the guy should have the right to defend himself.



  

aolmrd1241 OP
1,042 posts
 
Pins were clean. I swapped nos tubes one at a time and then listened...one at a time. Like I said 4 good and 2 noisy.  I have the 2 good nos Mullards running in the driver sockets and 4 stock ones in the 4  gain sockets  with another 12 hours of play time since I posted... Quiet as a mouse!


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