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ccockrell

DT50 112 humming badly - related to gain knob

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My DT50 112 started humming really loudly, all of a sudden.  It is only a couple of years old, and I don't gig with it, so it's been really taken care of.

It is humming really loudly, and the hum is affected by the GAIN knob.  If I turn up the GAIN, here comes the hum...but this is abnormally loud!

If I turn down the GAIN, the hum is reduced.

I'm guessing that it may be a ground issue, but I really don't know.  

Any recommendations on things to check or ground connections to tighten?

Thanks,
CajunChris

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How often do you play it since you got it?

When was the last time the tubes were replaced?

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Sound like a pre-amp tube to me, but no guarantee.

I would change and bias all power tubes and replace pre-amp tubes.

If this does not remedy the situation take it to an authorized line 6 repair shop.

Best of luck.

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Use the factory Electro-Harmonix tubes. These amps don't like modifications.

The digital and analog sections have to play nice with each other, so don't deviate from that.

 

12AX7EH Electro-Harmonix for the pre-amps

EL34EH Electro-Harmonix (matched pairs) for the power tubes

 

Have it biased by a Line 6 authorized service center. The high voltages in this thing are dangerous.

And it really hurts if you get zapped. Really hurts.

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The amp is only a couple of  years old.  I don't use the amp daily, but regularly.

There have been times when it's sat for weeks, then times when I play it 3-4 times per week.

And the hum is related to the gain knobs on both channels.  When I turn down the gains, the hum is reduced as well.  Would this narrow down which tube to replace?

I'm no expert, but it seems rare that a tube(s) would need replaced so quickly, doesn't it?

Thanks in advance for the info/advice!

CajunChris

 

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Tubes should be changed out every 18-months for regular gigging musicians,

every 20-22 months for weekend warriors and every 24 months for bedroom rock-stars.

 

You sound like a 20-22 month person. It's time for the tubes. Do not deviate from the

specified tube listed above. These are not the all analog tube amps of the 1960's and 70's,

you can't get away with the same kind of tube swapping we did back then. Stick to the specified tubes.

 

Go to a Line 6 authorized service center, as they will know the product and what to do with it.

Don't put this off, worn tube in an amp can be a bad thing for the amp.

 

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Good to know!  Thanks for the info.

With all of the talk about the vintage tubes being so sought after, I didn't realize that the newer amps' tubes needed to be changed this often.  I will try that.

I'm assuming that your recommend changing all 4, vs. changing them one by one until I find the "culprit", correct?

CC

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"... I didn't realize that the newer amps' tubes needed to be changed this often."---

It's always been that way, going back to the 60' and 70's, it's just the nature of tubes.

Most tend to forget that fact. I'm 60+, been dealing with tubes since I was 15 or 16.

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Use the factory Electro-Harmonix tubes. These amps don't like modifications.

The digital and analog sections have to play nice with each other, so don't deviate from that.

 

12AX7EH Electro-Harmonix for the pre-amps

EL34EH Electro-Harmonix (matched pairs) for the power tubes

 

Have it biased by a Line 6 authorized service center. The high voltages in this thing are dangerous.

And it really hurts if you get zapped. Really hurts.

Should I use the "soft, medium or hard" EL34EHs?

I like the tube crunch at lower volume levels, but I want to get what's best for the amp.

 

 

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Mediums, definitely mediums.

 

Besides the slight variations in the characteristic curves, that's another place where many problems

occur with other brands.

 

Those two aspects are amp killers when it comes to using something other than the specified tubes,... variations

in the characteristic curves between types brands and the gas-to-vacuum proportions.

 

That's why close enough with another tube,... isn't close enough.

 

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18 months between changes... wow.  I've had to change my dt25 tubes 3 or 4 times over the past 3 years.  I love these amps but they seem delicate.

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12-18 months if you're a gigging regularly musician.

 

No more delicate than any other tube for the last 50 years.

 

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