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talwilkins

Dt-25 Humming Loudly In Triode Mode

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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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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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When I first got my DT25 I thought it was humming more than it should have been in Triode mode. (AB was quiet). To make a long story short, by putting new tubes in the problem was significantly reduced.

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Thanks guys!

I don't know if there is a difference between A and AB.

I'll check it out and keep you posted.

I will also check the tubes. I have recently had a blown fuse so there may be something with the tubes indeed.

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The hum gets worse in Class A.

Time for a tube change. If you've had a fuse blow for no apparent reason and you are hearing humming, get those power tubes changed ASAP. I had the same issue.

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talwilkins, How many approx. hours do ya think are on those tubes?

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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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Stumblinman … yes, that really makes a lot of sense to buy 4 at once. Good move.

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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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If anyone is unsure wether their tubes are performing as they should

Google orange vt1000

Expensive but could save money in the long run

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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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Ahhh .,… the old "melting tube problem".... a classic … will definitely cause performance deterioration …. lol !!!

 

Lucky you had the JJ's on hand.

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