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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Need help with new tube for my amp

Josh05

Member
2013-05-22 3:40 pm
Hey guys, I've just recently brought a little desktop tube amp for my Grado SR225i's. I brought it off a website called Freds Amplifiers here is the exact model.

12AU7 Desktop Amplifier - $89.95 : Fred's Headphone Amplifiers

I'm really happy with how it sounds, my only complaint is having to wiggle or pull the tube out every now and then to stop the volume making a noise when i turn it up or down and to stop the occasional bit of noise coming through the headphones. So i was wondering if buying a better quality 12AU7 tube like this would be worth it or not? would it fix the problem and improve the sound? Any other suggestions and help would be awesome, I'm a massive noob with stuff like this. Thanks :)

Genalex Gold Lion 12AU7 ECC82 B749 Tubes Brand NEW Matched Sections | eBay
 
I doubt it's the tube. Noisy volume controls usually mean a dirty potentiometer or there's a bit of DC going through the controls. Being a new amp, a dirty pot is unlikely. There might be something wrong with the surrounding circuitry (bad solder joints or cabeling). Wiggeling the tube socket might just temporarily force the faulty joints together again. But it's hard to say without any schematics though.
 

Josh05

Member
2013-05-22 3:40 pm
I doubt it's the tube. Noisy volume controls usually mean a dirty potentiometer or there's a bit of DC going through the controls. Being a new amp, a dirty pot is unlikely. There might be something wrong with the surrounding circuitry (bad solder joints or cabeling). Wiggeling the tube socket might just temporarily force the faulty joints together again. But it's hard to say without any schematics though.

Thanks for the quick reply :) I might take it to a bloke my mum knows who is a retired electronics repairman, just thought i might as here first in case its an easy fix. Do you know if its worth replacing the tube in it with a better brand 12AU7 for better sound? Thanks.
 
Yes, I would check the tube socket and tube pins for corrosion and tight fit as well. Again, check these with the power off and the amplifier unplugged from the wall.

The amplifier seems to be powered by a 12V wall-wart. If the amp is plugged directly into a wall socket, it is possible that power switching transients from your mains is getting into the amp and causing occasional pops and crackles when other appliances in the house turn on and off.

Try using a different wall outlet or using a good, filtered power strip - the kind that you might use to protect a computer. Such power strips have transient protection that might help.

A UPS supply (like the computer backup power supplies) will provide very good isolation from line noise, but may be overkill.

The fireplace fan in my house causes the amplifier to really pop and sputter when it turns on and off - other heavy appliances such as a refrigerator, and even a simple lamp, can introduce noise when they turn on or off.

Good luck!
 
Thanks for the quick reply :) I might take it to a bloke my mum knows who is a retired electronics repairman, just thought i might as here first in case its an easy fix. Do you know if its worth replacing the tube in it with a better brand 12AU7 for better sound? Thanks.
Always a good idea to get a pro to take a look at it, but ask if you could take a look over his shoulder. Interestind stuff! :)
A 'better' brand doesn't give a better sound per se. It also depends on the way the tube is used within the circuitry. There are ways to make any tube amplify very linear, or to shine with all its non-linear glory. But heel, give it try. It's always nice to experiment.