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Dt-25 Humming Loudly In Triode Mode


talwilkins
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If it's recently started, I would lean towards eminent tube issues. Unless your amp has been subjected to abuse recently. Any difference between class a or a/b?

My DT-25 suddenly started humming loudly in triode mode. The penthode mode is still as quiet as ever.

Nothing really influences the hum. Even if I turn the master down completely it hums just the same.

What could be causing this?

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I don't know really.

I put new ones in somewhere at the beginning of 2013 i think.

We try to practice once a week, so I guess we played about 35 tot 40 times for 4 hours.

That would be 140 - 160 hours.

The I play a bit at home so I guess 200 hours would be a realistic guess.

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Tal …. I think a new set of tubes are in your cards? Keep the old ones for emergency spares. One suggestion from another forum member is to buy a matched set of 4 x EL84's then you have new spares when needed or an available pair for your next change over. Re-biasing is recommended with any tube change. As I mentioned before, my problem with humming in Triode mode went down "significantly" after a tube change but did not disappear totally. AB always remained virtually silent. The low level hum I still get a bit in Triode mode is more than acceptable compared to what I had before. Let us know how you make out with this problem after you put the new tubes in for our reference on this issue.

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That's how I do it, buy matched quad for quick swap should one fail during a show.

 

Tal …. I think a new set of tubes are in your cards? Keep the old ones for emergency spares. One suggestion from another forum member is to buy a matched set of 4 x EL84's then you have new spares when needed or an available pair for your next change over. Re-biasing is recommended with any tube change. As I mentioned before, my problem with humming in Triode mode went down "significantly" after a tube change but did not disappear totally. AB always remained virtually silent. The low level hum I still get a bit in Triode mode is more than acceptable compared to what I had before. Let us know how you make out with this problem after you put the new tubes in for our reference on this issue.

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I don't know really.

I put new ones in somewhere at the beginning of 2013 i think.

We try to practice once a week, so I guess we played about 35 tot 40 times for 4 hours.

That would be 140 - 160 hours.

The I play a bit at home so I guess 200 hours would be a realistic guess.

 

That's alot of hours of playing. Think you got your monies worth outta those tubes. Thumbs Up To YA.  I'm going to buy matched Quad set like Stumblinman suggests when I finally service my DT50 Head.

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I changed tube today and all is well :)

I started with measuring the bias on the old ones and Tube 2 was on 7,6 mV!

So, I took it out and found the following:

 

post-90313-0-04935800-1390144579_thumb.jpg

The glass of the tube is actually melted B)

 
Anyway, I still had some barely used JJ's and decides to give them a try.
I'm rehearsing tonight and can't wait to hear what they sound like!
I'll keep you posted.
 
 

P.s. Apparently I can't have the picture in the text without it also showing up under "attached thumbnails". A bit annoying <_<

post-90313-0-04935800-1390144579_thumb.jpg

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Good post talwalkins, I have already a spare set of original replacement tubes for my DT50 and am going to use them when the time is right for me, after that I'm going to use a different maker. I don't use my amp as hard as you do at the moment.

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Well, the DT-25 performed very nicely tonight.

The JJ's sound great! A bit clearer and an little bit more definition than the Electro Harmonix.

My presets needed a bit of tweaking because of it but I was very content in the end B)

of course it could also be just because they are new. I don't know really. T really hear the difference you would need two DT-25 amps with different tubes in them.

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