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Emergency amp help: Fender DRRI, no sound, no AC light, rectifier lights up


Poparad

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I have a CD release show tomorrow with my band, and tonight during rehearsal one of my DRRI amps went out. I run two in stereo, so worst case I'll have to run one amp and crank it, but I prefer to run two, both for stereo effects and fuller sound.

 

The sound went out, the AC light is off, and all of the tubes went out, except for the rectifier tube, which still glows strong. Any thoughts as to where in the chain the problem might lie?

 

The tubes aren't too old (6 months), and are a good set (full compliment of gold pinned JJ's). I had the amp recapped last summer, too. I bought the amp new in 2002, and have gigged with it very heavily.

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Some/most amps have internal fuses. I dont know for sure if your does... But Since you are still getting power to some parts of the amp its a good chance a fuse blew.. But fuses generally dont blow for no reason.. If you are comfortable opening your amp up and pulling out the chassis(if need be, perhaps there are fuses located where you can see them?) then pull out the chassis and look for fuses and check them.. Personally I would replace it if it is bad and hope it was a isolated incident. If it blows again, then look at power tubes being the culprit..

 

Just a somewhat educated guess..

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I have a CD release show tomorrow with my band, and tonight during rehearsal one of my DRRI amps went out. I run two in stereo, so worst case I'll have to run one amp and crank it, but I prefer to run two, both for stereo effects and fuller sound.


The sound went out, the AC light is off, and all of the tubes went out, except for the rectifier tube, which still glows strong. Any thoughts as to where in the chain the problem might lie?


The tubes aren't too old (6 months), and are a good set (full compliment of gold pinned JJ's). I had the amp recapped last summer, too. I bought the amp new in 2002, and have gigged with it very heavily.

 

 

As ENdtime said, check fuses. It should be noted though that there is really no such thing as a "good set" of tubes. Tubes can and do fail at any time and for what its worth, the only tube i've ever had that never worked, as in dead out of the box, was a gold pinned JJ 12AX7.

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Fortunately the DRRI has the fuse right on the back by the power switch, so I can pop it out easily. However, it will have to wait until morning because I don't have any spares to try.

 

 

Thats the mains fuse.. There can be fuses inside the chassis.. If the mains fuse blew, the whole amp would be out.. Internal fuses typically take out sections I.E. the power section/board of the amp when a power tube goes bad..

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You've probably got two fuses. A mains fuse and a high voltage fuse. The mains fuse is probably fine. That's what's powering your heater circuit (that's why everything is powering up) but your high voltage side isn't powering up. That's your HT fuse most likely although Fender may not do it that way.

 

It could be something else but I'd start there. Luckily you have a backup amp. Get slo-blo fuses.

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Well, I opened up the chasis and there is indeed another fuse on the board, but it looks to be fine. The filament is intact as far as I can tell. Surveying all of the other pieces of the board, nothing is obviously burned out or damaged looking. In fact, everything still looks brand new. The power light is wired to one of the two power tubes, which explains why it's not lighting up. If the power tube is not getting any power, then the light obviously won't, either.

 

Since the fuse seems fine (although I'm going to get some spares in the morning to test out, and just to have on hand. I can't believe I don't already), I'm guessing maybe it's just a bad tube. I have a few old ones I can plug in and try. The trouble with the JJs I currently have in it is that the tips are painted with a silver coat, so I can't tell if they blew. I have had a blown tube before, and there's usually a scorch mark on the tip of tube (if I'm remembering it correctly. It's been a few years since that happened).

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Don't overlook the obvious: check and make sure that the speaker cable isn't unplugged from the back of the chassis, which can happen when it gets jostled around in transit. It's not likely, but check it anyway. I own a DRRI myself, and I forget whether the speaker is connected to the cable via clips, but check those as well...make sure the cable is attached to the speaker.

 

If all seems fine there, start with a known good 12AX7 or 12AT7, and start working your way down the line with it.

 

Have you tried both the "Normal" and "Bright" inputs? If your "Bright" gives you sound, and the "Normal" doesn't, it's almost certainly a pre-amp tube failure.

 

I use JJ's as well, and I too have had them fail...preamp tubes, that is. Never had a GZ34 or 6v6 from them go on me yet. But at least 2 12AX7's have unexpectedly gone tits-up.

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OK, so I swapped out two extra sets of power tubes and nothing. I'm going to try some new fuses in the morning, as maybe it really is burned out but doesn't look that way.

 

 

Generally a Multimeter is the only sure way to check a fuse.

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Correct me if I'm wrong, but if the fuse goes...that's it. You won't even get the rectifier lighting up.

 

 

Depends on what they fused. If the heater circuit is live but your high voltage circuit is all dead your tubes will all light/warm up but when you switch off standby you'll get nothing.

 

Most amp builders/manufacturers have multiple fuses.

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My guess:

 

The 6.3 filament supply to all the tubes is either shorted (or more likely disconnected).

 

A tech can test for this with a mutimeter

 

The rectifier uses a different 5V filament supply off the power transformer(so it lights)

 

The pilot light and all the other tubes are fed from the 6.3v secondary.

 

That way you get NO SOUND and all but the rectifier not lit up.

 

 

You might need a new power transformer. This isn't such a bad thing. Replacing one with a better quality one upgrades the amp's sound a tad. They run around $100 but getting a tech to install one might be pricey.

 

Either the supply is shorted out or you have a bad power transformer. A burnt fuse wouldn't allow the rectifier to light up.

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My guess:


The 6.3 filament supply to all the tubes is either shorted (or more likely disconnected).


A tech can test for this with a mutimeter


The rectifier uses a different 5V filament supply off the power transformer(so it lights)


The pilot light and all the other tubes are fed from the 6.3v secondary.


That way you get NO SOUND and all but the rectifier not lit up.



You might need a new power transformer. This isn't such a bad thing. Replacing one with a better quality one upgrades the amp's sound a tad. They run around $100 but getting a tech to install one might be pricey.


Either the supply is shorted out or you have a bad power transformer. A burnt fuse wouldn't allow the rectifier to light up.

 

 

That makes sense. I just remembered that a rectifier tube heater circuit runs off 5v while the rest of the tube heaters run off 6.3v in many amps (barring elevated heaters obviously) so it very well could be the PT.

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Status update: I replaced the internal fuse and everything is working fine now. I guess that means the transformer is intact. I'm hoping it was just an isolated incident of a blown fuse. I'll have to play on it a bit today and see if it keeps.

 

Thanks for everyone's help!

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Ha! I was right...!

 

I'd like to thank everyone in attendance tonight.. Definitely props go out to Jesus and my dog Boozy...

 

 

Lol..

 

Hope it was isolated.. There actually has been a time or two when the fuse has blown and once I replaced it there have been no additional problems.. But other times, it ended up being the power tubes. Keep an eye on your power tubes and listen to make sure it sounds right.For example there have been times it blew an internal fuse and when I replace it, the amp works, but only 3 power tubes were running because it also took out a Screen Grid Resistor when the tube went bad. Also the tube would still light up, but when I took the amp off standby only 3 tubes had that slight blue glow. Also when you really crank an amp up and play some quick chugs or loud chords you can see the tubes kinda lighting up as they are compressing.. If you notice one tube isn't reacting like the others, then its possible its not working. There is also a way to read the SGR with A multimeter, but if I don't have one then I look for that little blue glow and also watch the tubes at loud volumes..

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In the past, I've blown a few grid resistors with bad power tubes. :mad: I fortunately do have a tube socket adapter for my multimeter that I use for biasing, so I should be able to tell if both tubes are getting full power.

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Both are fine, although they are running really cold. The bias is maxed out and they're only running at 20. Usually maxing out a DR would put them around 30+. Maybe they're getting worn out and that affected the amount of power being drawn? I had the amp up fairly loud when it blew last night.

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