No More Hiss W/ New 12ax7 Tubes.

[bribrew1968]

DT50 212 --- amp went out on me after about 2 months, a quick gurgle as tubes burned out ... then nothing. Thusly, I looked at the tubes ... the EL's were glowing bright, 12AX7's were out. Went to Guitar Ctr and after being assured they'd work, I got the Groove Tube russian brand. I would avoid chinese brands also. Russian just seems better sounding to me. Easy to replace and took about 1 minute of careful pressure to install.  Unplug too ... duh?!  LOL. 

 

I immediately noticed that the factory 'hiss' was nearly gone (like 90%), and the sound was more colorful. I looked online and noticed the EH stock brand was much cheaper than the GT brand.

 

As well, each topology was more defined.  3 and 4 are now my fav's.  Wonder how the sound will be if I replace the EL's with a high quality brand?

 

Bribrew

[toneman2121]

http://www.thetubestore.com/12AX7-Tube-Review

[bribrew1968]

http://www.audioasylum.com/reviews/Tubes/Groove-Tubes/12AX7-M/tubes/172557.html

 

Found this too.  Still stunned by the quietness of this amp now (until I hit the strings LOL).  Mullard tubes seem to be the name everyone likes though.  I am impressed and just got a major education on pre amp tubes.

 

My DT50 212 sounds like a symphony ... of destruction ... LOL.

[toneman2121]

that site also has reviews of other tubes, 6L6,el34, etc,  http://www.thetubestore.com/Resources/Product-Reviews, 

[swing_girl]

DT50 212 --- amp went out on me after about 2 months, a quick gurgle as tubes burned out ... then nothing. Thusly, I looked at the tubes ... the EL's were glowing bright, 12AX7's were out. Went to Guitar Ctr and after being assured they'd work, I got the Groove Tube russian brand. I would avoid chinese brands also. Russian just seems better sounding to me. Easy to replace and took about 1 minute of careful pressure to install.  Unplug too ... duh?!  LOL. 

 

I immediately noticed that the factory 'hiss' was nearly gone (like 90%), and the sound was more colorful. I looked online and noticed the EH stock brand was much cheaper than the GT brand.

 

As well, each topology was more defined.  3 and 4 are now my fav's.  Wonder how the sound will be if I replace the EL's with a high quality brand?

 

Bribrew

 

 

Hi Bribrew,

 

I found your post while searching for solutions to DT50 combo amp hiss.  I would like to know if replacing the tubes just a process of unplug and plug in? Do I need to do anything like biasing the tubes? because I do not know how to do this.  Thank you for any advice.

[egkor]

For the 12AX7 tubes, it is remove & replace.

 

For the EL34 tubes, you would remove, replace, and check/set bias. Bias is best done by trained amp tech.

 

Tubes pull straight out to remove. Their pins are keyed so they can only be inserted one way in the socket.

 

Thier pins can bend & break, so be careful when re-installing.

[swing_girl]

For the 12AX7 tubes, it is remove & replace.

 

For the EL34 tubes, you would remove, replace, and check/set bias. Bias is best done by trained amp tech.

 

Tubes pull straight out to remove. Their pins are keyed so they can only be inserted one way in the socket.

 

Thier pins can bend & break, so be careful when re-installing.

Thanks.  I could not find any replacement tubes in music shops here; I removed the 12AX7s and plugged them in again, the hiss is mostly gone.  However, I feel that the volume seems to have dropped, could it be that I did not check whether the pins went into the same socket as before?

[egkor]

Swing_girl,

 

A tube will only allow itself to be inserted in the correct orientation in its socket.

 

I can't explain why you have a volume drop, this also might be why you percieve less hiss.

 

Check to see if you didn't accidentally put the DT into "low volume" mode at the front panel of the DT50.

 

:)

[swing_girl]

Egkor,

 

Thanks for your reply.  I put the tubes back in and they are secure.  The volume loss is a feeling I have but since I have not measured the volume level pre and post tampering the tubes, I have no idea how much is really lost.  However, I am very happy with the hiss much lowered.

 

:-)

[egkor]

swing_girl,

 

Removing and re-inserting the 12AX7 tubes should give identical before/after results.  This should not result in a volume loss.

 

I believe whatever the reason for the perceived/actual volume loss is also why the hiss is reduced.

 

I can't explain any of it as a result of only removing and reinstalling the (same) 12AX7 tubes.

 

But, if the hiss is reduced and the tone is still there (if it still sounds good) then, good!  :)

 

I have a DT50 Head, and it is noisy/hissy. So I know exactly what you mean by "hiss".  Once I start playing through it, I forget about the hiss.

 

May I ask, where are you that the music stores don't have replacement 12AX7 tubes?

 

Edit:  Also let me add, for the EL34 (big) power tubes, you can remove and replace the same tube(s) in the same socket(s) without a re-bias. But if you replace your EL34 tube pair, then a bias check/set is must-do.

[swing_girl]

egkor,

 

I have no idea why removing and inserting the same tubes got rid of the hiss, the tubes were not loose when I removed them.  The tone is still there so I am happy that most of the hiss is gone; even if the trade off is a little bit of volume loss.  I play with clean tones a lot so the hiss was really annoying.

 

I am in HK and there are two big music shop chains, they both have no stock of any 12AX7, or other tubes for that matter.

 

I am not going to touch the power tubes, they have a metal cage around them and I know nothing about re-biasing tubes.

 

Thanks again for advice :-)

[egkor]

Hi swing_girl,

 

HK! I have visited there in years past.

 

I hope I have been helpful to you.

 

My best wishes to you!

[CipherHost]

Hong Kong?

[mtreehugger]

egkor,

 

I have no idea why removing and inserting the same tubes got rid of the hiss, the tubes were not loose when I removed them.  The tone is still there so I am happy that most of the hiss is gone; even if the trade off is a little bit of volume loss.  I play with clean tones a lot so the hiss was really annoying.

 

I am in HK and there are two big music shop chains, they both have no stock of any 12AX7, or other tubes for that matter.

 

I am not going to touch the power tubes, they have a metal cage around them and I know nothing about re-biasing tubes.

 

Thanks again for advice :-)

 

swing_girl,

 

the only way that re-seating your pre-amp tubes could make any difference would be if there were a bad connection.  It is possible for the pins or their mating contacts to become corroded or tarnished, compromising the electrical connection.  This is rare, though, unless your amp is over 5 years old.  But if you are close to the ocean and your amp is exposed to salty air, then it's much more likely to occur.  

 

However, re-seating the tubes would tend to either eliminate static or other noise, or possibly boost power--if a pin wasn't making contact before and some of the signal was getting lost (can't say if this is even possible, as I'm not fluent in the operation of the pre-amp circuit).  It would not be likely to reduce hiss and volume.  The only scenario where that could happen is if somehow your connections were originally fine, but when you re-seated the tubes you either bent a pin or somehow introduced dirt or other contaminants into the electrical connection(s).

[swing_girl]

swing_girl,

 

the only way that re-seating your pre-amp tubes could make any difference would be if there were a bad connection.  It is possible for the pins or their mating contacts to become corroded or tarnished, compromising the electrical connection.  This is rare, though, unless your amp is over 5 years old.  But if you are close to the ocean and your amp is exposed to salty air, then it's much more likely to occur.  

 

However, re-seating the tubes would tend to either eliminate static or other noise, or possibly boost power--if a pin wasn't making contact before and some of the signal was getting lost (can't say if this is even possible, as I'm not fluent in the operation of the pre-amp circuit).  It would not be likely to reduce hiss and volume.  The only scenario where that could happen is if somehow your connections were originally fine, but when you re-seated the tubes you either bent a pin or somehow introduced dirt or other contaminants into the electrical connection(s).

 

I think you are probably right; I could have bent a pin when I re-seat the tubes.  The tone is still good and I am happy that loud white noise style hiss is mostly gone.

[mtreehugger]

I think you are probably right; I could have bent a pin when I re-seat the tubes.  The tone is still good and I am happy that loud white noise style hiss is mostly gone.

 Just curious--where is your pentode/triode switch set, and does the amount of hiss change when you switch it?  (this is a power tube thing, not a pre-amp thing, but still...)

[swing_girl]

 Just curious--where is your pentode/triode switch set, and does the amount of hiss change when you switch it?  (this is a power tube thing, not a pre-amp thing, but still...)

The hiss was very loud in both modes and also across all 4 amp types before I re-seat the pre amp tubes.  Like I said, I may have bent some of the pins but I am happy that hiss is almost all gone and the drop in volume is hard to measure, it is not very significant but it seems to be there only.

[mtreehugger]

The hiss was very loud in both modes and also across all 4 amp types before I re-seat the pre amp tubes.  Like I said, I may have bent some of the pins but I am happy that hiss is almost all gone and the drop in volume is hard to measure, it is not very significant but it seems to be there only.

 

With what you're reporting, I'm now doubting you bent a pin.  If a person is at all careful, it's next to impossible to bend a pin.  If you are in a coastal area where the air is salty from the sea, your electrical contacts would probably tend to pick up more contaminants and corrosion than average.  when you re-seat your tubes, you are actually cleaning those contacts, so doing what you did would be a good thing, and one that you probably should repeat if you encounter those same symptoms in the future.

[swing_girl]

With what you're reporting, I'm now doubting you bent a pin.  If a person is at all careful, it's next to impossible to bend a pin.  If you are in a coastal area where the air is salty from the sea, your electrical contacts would probably tend to pick up more contaminants and corrosion than average.  when you re-seat your tubes, you are actually cleaning those contacts, so doing what you did would be a good thing, and one that you probably should repeat if you encounter those same symptoms in the future.

 

You are right, I live right next to the sea.  I am not a technical person who knows about tubes and schematics; I will find someone more knowledgeable to do it if the hiss returns.  Thanks  :)  :)  :)