Can A Blown Power Tube Or Tubes Cause Damage To My Dt50 Head?

[Brazzy]

    I don't play everyday, but when I do it's for about an hour or two. I rarely run it with the Master Volume past 12 O'clock as with the Channel Volume, for now.

 

    I'm gearing up to get Biasing tools so I can be able to check and/or set it when the time comes for power tubes to be replaced. Any comments or recommendations are always helpful.

 

     If the fuse blows what should I replace it with, (value)? I haven't taken it out to look it over. I hope I don't need to but ya never know, it pays to try to be prepared.

 

 

I found this info pertaining to what to look for just before it come time to service the amp with new tubes. There's a lot more to the article. If you want to read it all click the link below.

 

Tube Frequently Asked Questions

Replace the tubes when:
* It is broken, and/or there is a white spot on the top or sides of the tube. The "getter" coating found in these areas is normally black or silver colored. By the way, a chocolate brown getter simply means the tube has had a lot of use. It still may test good.
* It tests weak or shorted. Always use a "mutual conductance" type tube tester for testing. Cheap emission type testers with "good/bad" meters are almost useless. Always replace a shorted tube, even if it tests good. Shorts can damage expensive amplifier parts.
* You cannot afford to lose your amplifier during a performance. Professional players minimize downtime by replacing the power tubes every few concerts, and by using several amplifiers. The price of tubes is cheap compared to the embarrassment of losing an amplifier on stage!
* The amplifier starts to sound bad, especially when first turned on.
So how do you know when tubes are starting to fail? Consider the following:

Small-signal (preamp) tubes (12AX7, 12AU7, 12AT7, 5879, etc.): You may hear a crackle for a short time after the amplifier is turned on. Then it quiets down. Or the amplifier may "howl" at high volumes, or buzz on certain notes all the time. These problems get worse, and eventually you will be replacing one or more tubes.

Power tubes (6L6, 6V6, 7027, 6CA7/EL-34, 6550/KT-88, etc.): Upon turning on the amplifier, the sound may be hazy, with flabby bass and scratchy treble. After about five minutes of this, the sound starts to clear up, and the amplifier sounds fine from then on. As the tubes get weaker, it will take longer for the sound to clear up. Eventually you have to replace the power tubes as a set. For reliability we strongly encourage you to replace all power tubes at a time, even if one or more tubes are still good. Also, make sure your technician set the bias correctly after they are installed. You may keep any good tubes as spares for emergencies, though.
 

© Doug Roccaforte
www.RoccaforteAmps.com

This article is written by Doug from Roccaforte Amps and was posted at the Harmony-Central Forums and was used for this site without his explicit permission.

[stumblinman]

The fuse ratings are on the back of the amp near the fuse holders. There is potential for a failed tube to damage an amp, but you really just have to trust that the fuse will blow before damage can occur.

[Brazzy]

The fuse ratings are on the back of the amp near the fuse holders. There is potential for a failed tube to damage an amp, but you really just have to trust that the fuse will blow before damage can occur.

 

Hey Thanks, I just took a look and took a picture so I don't have to move this Beast of an Amp Head again anytime too soon, LOL. Looks like it reads "T1.0AL / 250 V Slo-Blo Fuse".

[radatats]

When you are ready to change tubes...

 

http://line6.com/support/topic/3327-dt-50-25-tube-biasing-tips/

[Brazzy]

When you are ready to change tubes...

 

http://line6.com/support/topic/3327-dt-50-25-tube-biasing-tips/

 

Thanks for the reminder, I should have downloaded that when I visited that page you created a while ago, LOL. Awesome info Dude!!!

[stumblinman]

Hey Thanks, I just took a look and took a picture so I don't have to move this Beast of an Amp Head again anytime too soon, LOL. Looks like it reads "T1.0AL / 250 V Slo-Blo Fuse".

Fuse Rating DT50 Head.jpg

looks like you got both in the picture. The other is a 5A 250V slo blo below the plug. That's the one that blew when one of my power tubes went south.

[Brazzy]

looks like you got both in the picture. The other is a 5A 250V slo blo below the plug. That's the one that blew when one of my power tubes went south.

 

    Oh, I missed that one, glad you mentioned that. I was just reading an old post about the DT50 Tubes>> Here

   

I found this part interesting;

    "The two 12AX7 tubes are part of the power amp stage and not the pre-amp stage.  There are no tubes in the pre-amp stage,  One of the tubes brings the level from the solid state pre-amp stage up to that required to drive the power tubes and the other 12AX7 is an inverter."

 

  

Interesting old threads

Re: Another DT50 question

by Nick_Mattocks

on 2011-06-21 14:36:39

 

Bias is adjustable when the amp is running class A/B mode but not when running in Class A mode as I understand it.  There are bias adjustment pots and test points inside.

 

I don't know of anyone who has tried KT77s in their DT50.  I'm still on the original EL34s as fitted at the factory.

 

Pin for pin the KT77s are a match for EL34s.  However, even with EL34s there's a whole range of different spec valves available.   I wouldn't like to recommend that you try any other valve type than that which is already fitted - yes a different brand for sure if you wish, but the electrical specification should be the same as what's fitted to ensure that damage doesn't occur to your amp - particularly with respect to the output transformer.

 

You'd need to pose your query specifically as a question and you may get a response from Line 6 Customer Support who will be able to check out your question out with the people who will know whether you will be safe to try a pair of KT77 tubes

 

The two 12AX7 tubes are part of the power amp stage and not the pre-amp stage.  There are no tubes in the pre-amp stage,  One of the tubes brings the level from the solid state pre-amp stage up to that required to drive the power tubes and the other 12AX7 is an inverter

 

Nick

 

[TheRealZap]

+1 for quoting the great Nick Mattocks.

 

    Oh, I missed that one, glad you mentioned that. I was just reading an old post about the DT50 Tubes>> Here

   

I found this part interesting;

    "The two 12AX7 tubes are part of the power amp stage and not the pre-amp stage.  There are no tubes in the pre-amp stage,  One of the tubes brings the level from the solid state pre-amp stage up to that required to drive the power tubes and the other 12AX7 is an inverter."

[stumblinman]

+1 for quoting the great Nick Mattocks.

His disposition and exposition is missed.

[Brazzy]

When I was learning how to play guitar and use these Line 6 devices I would frequent this site to learn about things I didn't even have yet, LOL. Nick was one of those guys that wrote posts I would read and learn from. He wasn't the only one that taught me without knowing me though, there are plenty of knowledgeable people floating around here and I thank each and every one of them here and now. I still have a lot to learn, but You all have helped me greatly.

 

+1 for quoting the great Nick Mattocks.

His disposition and exposition is missed.