Author Topic: Mullard 12AU7s Have Arrived!  (Read 16834 times)

tanchiro58

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Re: Mullard 12AU7s Have Arrived!
« Reply #30 on: February 02, 2008, 06:31:10 AM »
Hi Ken,

Have you tried rolling with Tungsram 12AU7s yet? IMO I prefer Tungsram's sweetness over Mullard NOS.

Tan

Bigfish8

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Re: Mullard 12AU7s Have Arrived!
« Reply #31 on: February 04, 2008, 05:21:53 PM »
Hi Ken,

Have you tried rolling with Tungsram 12AU7s yet? IMO I prefer Tungsram's sweetness over Mullard NOS.

Tan

Hello Tan:

I have been out of the audio picture for approximately a month as I was only obtaining a hum (no sound at all) from my preamp.  I sent it back to AlexG of Odyssey and he determined the problem to be oxidized tube pins.  Unfortunately, I did not know that I needed to clean the pins with a deoxidit and then polish them with a contact enhancer.  Anyway, the wife tells me the preamp is back home and I am looking forward to getting back home and listening to some tunes. 

Until I read your message I had not even heard of Tungsram 12AU7 Tubes.  I will have to put them on my list to try.  Also, why I was talking with Alex he recommend the new JJ 802s which are the long plate version of the standard 12au7.  He claims they are darn good and reasonably priced!

Take Care,

Ken

Offline Carlman

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Re: Mullard 12AU7s Have Arrived!
« Reply #32 on: February 04, 2008, 07:32:44 PM »
Wow, Ken... those must have been the dirtiest pins in the world!   :shock: 
It has not been my experience that dirty pins cause a preamp to hum with no other sound.
-C
I really enjoy listening to music.

tanchiro58

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Re: Mullard 12AU7s Have Arrived!
« Reply #33 on: February 04, 2008, 11:30:31 PM »
Wow, Ken... those must have been the dirtiest pins in the world!   :shock: 
It has not been my experience that dirty pins cause a preamp to hum with no other sound.
-C

Carl,

It happened to my tube amp before. I did not get a hum but a buzzing sound and sometimes no sound at all. It was the dirtiest tube socket (one only) I ever had. I thought my tube was kaput but I got solution from my friend by cleaning it with deoxidit.

Offline Carlman

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Re: Mullard 12AU7s Have Arrived!
« Reply #34 on: February 05, 2008, 05:19:55 AM »
I had no idea we were such a dirty bunch! ;)
 :lol:
I really enjoy listening to music.

Offline richidoo

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Re: Mullard 12AU7s Have Arrived!
« Reply #35 on: February 05, 2008, 06:31:15 AM »
On tube power amps were have a B+ fuse which when blown stops the music, but the hum can still be heard. I wonder if such a fuse is in your preamp? It is good to have you back Ken, I was wondering what happened to you!

Bigfish8

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Re: Mullard 12AU7s Have Arrived!
« Reply #36 on: February 05, 2008, 06:41:25 PM »
Wow, Ken... those must have been the dirtiest pins in the world!   :shock: 
It has not been my experience that dirty pins cause a preamp to hum with no other sound.
-C

Carl:

I was totally shocked when Alex called me and told me what he had found to be the problem with my preamp.  I played the system on a Monday before I left home.  When I returned on Friday I turned the system on and after warm-up all I got was a hum (volume controlled) in the right speaker.  I changed tubes from Mullards to Amperex and with no change in the hum (no sound but hum).  I spoke with AlexG on Saturday and he was able to hear the hum through the telephone and said send the preamp back to him. 

After receiving the preamp Alex called me and reported that the preamp was now working fine.  He said he cleaned the tube pins with deoxit and then polished the pins with a contact enhancer.  Alex also told me that the pins on the JJ Teslers slightly larger in diameter than the pins on the European NOS Tubes.  Therefore, he claims I need to be very careful when rolling tubes to ensure the pins are seated well and making contact.

Anyway, I learned from the experience and will not, I repeat will not, roll tubes without cleaning the tube pins and polishing them with a contact enhancer.  I, having an engineering background, prefer to have an explanation why the Mullards worked fine for 2.5 months and then suddenly I get the hum.  The only things I can think of are that I moved the preamp in cleaning it and possibly the room experienced colder temps that week because it was the only cold spell we have had.  Other than those two things all I did was turn the unit on and off.

Oh well, I hope it works well when I get back home tomorrow night!

Ken