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Advise on tube el34 and 12ax7

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Just got 2 Tung Sol 12AX7 and got it replaced with my existing EH tube.

However when I on it, I checked but notice it did not lit up which

I thought was normal as the last tube my last EH 12AX7EH tube is very dim/

But after around 5 mins, when I notice some burn smell and shortly there is a sharp pop sound coming

from my amp. I got shocked and immediately turn the power off.


The guy who told me the replacement of my preamp tubes, 12AX7 and 12AU7 was a simple task.

Just replace and not adjustable needed. Is that true ??


After I replaced with the old EH ones, everything was fine. The only prob. I guess must

be from the new Tung Sol preamp tubes I bought man.


Anyone can advise what happen ? Think I have to go back to the shop I bought it man !!

Is is a good idea to replace my stock 12au7 with EH reissue ones ?


Tks in advance  >:(


My earlier post >>


Would like to seek further advise of tube change as saw lots of post

on tubes. Current using A50T with Monitor 7 speaker.


Any suggestions and review on your recommendations ?


I am considering quad matched Mullard EL34, EH EL34H or the JJ KT77 ( reissue )

Feeling confused !!


Where is a good place to get in SG ?


Anyone used these tube above ? wondering how good a improvement would

it make ?


Is it a must to bias amp whenever changing new tubes ? Matched

tubes need bias too ?


Tks in advance !!  ;)



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Hi channelg

Welcome to Xtremeplace, where advice is by the bucket loads but not necessarily what you need.

Before anything else, what kind of sound are you getting?

And what improvements do you expect to get?

What kind of source are you using; CD or LP?

What kind of music do you listen to most of the time critically?

What type and brand of small signal tubes or input tubes are in the amplifier?

Mind you that different brands will give give different sonic results in different setups so YMMV. The only way is to try. However, do a search in other forums to get a general consensus. Also do take note that your small signal tubes also play a big part in giving you  your amplifier's sonic signature. Have I mentioned the internal passive components too?


Biasing is about ensuring all your power tubes are operating at their optimal based on the amplifier design's parameters. Basically, you set the amount of current that is going into your tubes. It should be all the same. Since it's quite tedious to measure it, most designs use voltages to represent the current drawn by each tube.

You do need to bias your tubes once a new set is replaced, a few times in fact, in my honest opinion.

The first time is usually 10 minutes after the amplifier is switched on.

The next is 1 hour later.

The third is a week later to make sure everything is stable.

Subsequently, every 6 months or 500 hrs as these tubes do wear out.


Try not to switch your amplifier on and off too many times as this can wear out your tubes faster.


Hope this helps.

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Hello ,

best tubes is Mullard EL34

you bias the tubes not the amp

some tube amp you can bias the tube , some can not.

those can not , you need to get a meter.


I am using this set up method


player > equalizer > active sub woofer > EL34 tube amp > book shelf speakers

Intergrated amp you have bass, mid and treble control.

tube amp does not have such control but the vocal is very live and real

if you add an equalizer you have the best of both worlds.

have a try.


EL34 tubes you can get at Martin in Burlington Square.

I got mine Selvantek quad for $50 only.


I enjoy most watching Concert DVD on 100" inch projection screen with such set up.

better than DVR DTS , with air con , feeling like in the pub.


just my opinion, as most tube lovers do not agree as they prefer pure and orginal music.


:D :D :D

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Nice amp. Used to own one.


Besides the tubes you mention, also consider the EH 6CA7.


And do consider changing your preamp / driver 12AU7 and 12AX7 tubes too.


Bias on the A-50 is easy since you have individual trim pots. Whether matched or not, you must still bias the tubes. Also experiment with different bias levels. As a starting point, try between 0.32-0.35V.



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  • 1 month later...

Hi, I am new for the tube AMP, I have planned to replace my RUBY 12ax7 HG tube to Tong Sol tubs that I heard peoples said it sounds better than RUBY's. Is there anyone know where can I buy these tubes in Singapore? One more question, my AMP is Dared I30 and vendor said it is auto biased, does it means I can swap the tube as long as model name is the same?? Thanks

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