Amps Not again, Line 6- DT50 this time.

[CapnDenny1]

Customer came and fetched his DT-50 Monday. I left it on the porch. He picked it up, and left a Line 6 - DT50 head. Same symptom, blows fuses. It doesn’t appear to be the ceramic caps. At least this one, being a full length head, isn’t all folded up. That will make it easier to debug.

I asked to let me know if the DT25 is fixed? I was concerned about the volume drop between modes. He said that was how it was.

D9F7DD02-5C69-42FC-B961-405C0064E99E by Dennis Kelley, on Flickr

 

[CaptainMoto]

The only thing I can understand in that picture is..............the bananas.

 

[OG_Blues]

I see that amp was made by Bogner for Line 6.
Bogner makes some pretty pricey amps under their own name/brand.
They should know what they are doing. Looks like a lot of relays in this amp too.
Time to break out your current limiter again!!!

 

[CapnDenny1]

I believe Bogner did the tube amp portion?

The relays are used to switch the preamp configuration, and the class A or AB, and the triode or pentode mode.

The DT-25 was a nice sounding amp. Just really complicated.

 

[OG_Blues]

The Manufactured by Bogner label is on the edge of the main PC board at the bottom of the picture you posted.
What is the tube complement?

 

[CapnDenny1]

It says it has 2 12ax7 and 2 el34 tubes.

 

[CapnDenny1]

I found a blown fuse. It had a 3A fuse on the ac input. It was supposed to be 5A slo blow. I don’t have a 5A slow blow so I put in a normal 5A fuse and the amp seems to be ok. So I ordered some of the correct fuses. I will check the bias current and put it back in the cabinet. Once the correct fuse arrives I will do a bit more testing.

I asked the customer if he was driving it really hard when it failed? He said no, all he did was power it up and it was dead. One of the issues in electronics is what is called “in-rush current”. When you power up a device it draws an initial current which is much higher than the normal operating current. This is a 50W amp, so even if you assume a power consumption of 200w at full power, that is less than 2A current draw. But at startup it may draw much more than 2A. It most likely draws more than 5A, hence the need for the slo blow fuse.

So basically it is important to use the recommended fuse, both in the current rating, and amount of time delay.

 

[aleclee]

I see that amp was made by Bogner for Line 6.
Bogner makes some pretty pricey amps under their own name/brand.
They should know what they are doing. Looks like a lot of relays in this amp too.

The Manufactured by Bogner label is on the edge of the main PC board at the bottom of the picture you posted.

The PCB might say "Manufactured by Bogner" (though I only see "Designed by Bogner for Line 6" in this pic) but I'm pretty sure it was L6 that did the PCB layout if not the actual manufacturing. At the time, Bogner had a deal with L6 for (his) tube amp design services and (L6's) distribution.

 

[CapnDenny1]

Put the correct fuse in. Checked the bias, all good. Put it back in the cab. Told the customer it was ready. Tested it.....and nothing but hum?

So I will take it back into the shop. Unless it accidentally falls down the stairs! Oh darn!

I hate these amps, but they do sound pretty good, and the variations are all a little different. But dang it, what a mess.

One of the things I like about tube amps, at least, normal tube amps, is that they are pretty simple. They are the result of 100 years of continuous improvements in design and materials and peaked about 50 years ago. But compared to things like this amp, and even more so, the newer modelling only amps, they are simple.

 

[OG_Blues]

The PCB might say "Manufactured by Bogner" (though I only see "Designed by Bogner for Line 6" in this pic) but I'm pretty sure it was L6 that did the PCB layout if not the actual manufacturing. At the time, Bogner had a deal with L6 for (his) tube amp design services and (L6's) distribution.

ya Alec - my bad - looks like it does say "Designed By" not "manufactured by" (partially obscured by the wire) - I jumped the gun. Can I blame my bad old eyes? Thanks for the correction.

 

[CapnDenny1]

What it should say is "Fixed by CapnDenny!"

It did not "accidentally" fall down the stairs. I found the issue. When I put it all back together I ended up bending the pins on the pcb for a 2 pin connector. It's the small white connector near the fuse on the left. Apparently, when I pushed it on, it went in a little way and then bent the pins over. So it seemed to be connected, but not far enough to make contact. I saw ti was a little misaligned, and when I pulled it off I saw the bent over pins. I straightened them out, and carefully put the connector in place, and she works now. Now PLEASE come take your amp away!

0C1AD7D1-6479-4ECA-B465-4EB55CC9BE72 by Dennis Kelley, on Flickr

 

[PapaRaptor]

Glad it was easily found!