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jws1982

Dead DT25 - What do you guys think?

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Hey guys,

 

I had my first problem out of my DT25 the other day, and it's a good one.   I turned it on, flipped the standby switch after it warmed up, got a loud hum from the speakers, then the amp shut off completely after a second or two.

 

Now it doesn't come on at all.  No power light, no sounds, pops, tube glow, nothing.  The tube protection fuse on the outside is fine (i replaced it just to verify), power cord's fine, tubes are fine (replaced those to verify as well), and speaker is fine. It was plugged into the amp properly too.  I haven't had much time to troubleshoot otherwise, but I did pull the chassis for a few minutes.  All wires/connections I could see looked good.  I didn't see any burn marks on the PCB's or components.

 

The problem feels like something early in the flow of the power section, like a blown fuse or component.  I guess i need to break out the multimeter and check some things.   Before I do though, are there any other internal fuses, or typical components that fail, that I should check first?  I must confess that I've never really dug into the internals of this amp, other than to bias the tubes.  It's been super-reliable so far, taking beatings from being lugged around for over a year.

 

For the time being, I've been using my backup amp, a Spider Valve 212 1st gen.  I must say, the POD HD500 going into the amp input of it sounds very good. :)   It stinks having to lug it through downtown Nashville though, even on a cart.  If I can't get the DT25 working again for a decent price, I may search out an SV 112 1st gen to replace it.  

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There are two fuses on the back of the DT25. One in a round receptacle labeled tube protection, and another directly below the power plug. That is likely the one that blew. My amp did exactly the same thing when my power tube went bad. Replace power tubes (and bias), replace fuse under power plug, and you SHOULD be up and running.

There are several old posts on this forum that state the current/voltage requirements of the fuses.

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There are two fuses on the back of the DT25. One in a round receptacle labeled tube protection, and another directly below the power plug. That is likely the one that blew. My amp did exactly the same thing when my power tube went bad. Replace power tubes (and bias), replace fuse under power plug, and you SHOULD be up and running.

There are several old posts on this forum that state the current/voltage requirements of the fuses.

Ahhhhh!!!!  I totally forgot about the fuse built into the IEC inlet!  Thanks for the reminder.  I'll check it tonight.  Then I get to find the actual problem that caused it to blow...

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I'm 99% sure, based on what you described, that a power tube change and fuse replacement will fix your issue. Like I said, that was identical to my experience.

 

Ahhhhh!!!! I totally forgot about the fuse built into the IEC inlet! Thanks for the reminder. I'll check it tonight. Then I get to find the actual problem that caused it to blow...

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IEC inlet fuse was blown.  I also found that the tube bias was way too hot.  The tubes tested fine in another amp, but I went ahead and replaced them in case of damage.  With new tubes, a new fuse, and a re-bias, everything's working great again.  

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Glad to hear it. Play on!

 

IEC inlet fuse was blown. I also found that the tube bias was way too hot. The tubes tested fine in another amp, but I went ahead and replaced them in case of damage. With new tubes, a new fuse, and a re-bias, everything's working great again.

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