DT50 replacement EL34 matched tubes tolerances

[muljator 0]

HI

I just got new JJ EL34 matched power tubes to install in my DT50.

When i went to bias the tubes i found out that the difference bettwen my matched pair is about 3mV.

I could set one tube to 36mV but the other would be 39mV.

Is this considered a normal tolerance for matched tubes, and will there be any trouble with my amp becouse of this missmatch?

The EHX tubes i had in the amp had a 0.3 mV difference.

Thx for your replies!

[Brazzy 439]

That's a good question. I posted my findings when I bought a pair of matched tubes. I'll dig up the post later. I had a similar mismatch if my memory serves me.

I put the matched set of tubes in my DT50 after I had an issue with the sound cutting out etc. After putting them in and biasing It worked, then shortly after that no sound again. I ended up having to send it in to Line 6 to get it fixed. Ultimately I wasted my money on those tubes, biasing tool, and my time.

I hope you get 'er fixed up this amp sounds fantastic when it's right and the one I got fixed has been working great. I'll be watching your thread too.

 

On another note, just recently I put an Electro Harmonix Tube EQ in the FX Loop of the my DT50HD and Peavey Valveking II 20 Mini Head and was really impressed with how they sound with those 2 extra tubes after the preamp.

 

My findings on the biasing, the following link should take you to the specific post:

http://line6.com/support/topic/6699-dt50hd-output-suddenly-went-silent-any-ideas-why-and-more/?do=findComment&comment=61241

[psarkissian 316]

This is the reason I tell people to use the EH tubes and not JJ's,

Groove Tubes or Mesa. A bias range+/- 3mV is too much. Bias distortions may

occur. Use the specified tubes. These are not tube amps from the

1960's where you can get away with tube swapping like this.

[Brazzy 439]

Oh crap, I misread this thread, lol. I missed the JJ part since the topic heading had EL in it. Oh well, lol.

 

To clarify on my end. I never used JJ tubes in my DT50. I bought what was advertised as ultra matched EH EL power Tubes for the DT50 and still had a very large mismatch. So I have to question wheater I was not getting the correct tubes even though I did as much as I could to get the original replacements. I seriously think I was sold tubes that were not as advertised, buyer beware.

 

To the original poster. I seriously recommend you let Line 6 fix your amp as this is what I did.

[muljator 0]

Oh crap, I misread this thread, lol. I missed the JJ part since the topic heading had EL in it. Oh well, lol.

 

To clarify on my end. I never used JJ tubes in my DT50. I bought what was advertised as ultra matched EH EL power Tubes for the DT50 and still had a very large mismatch. So I have to question wheater I was not getting the correct tubes even though I did as much as I could to get the original replacements. I seriously think I was sold tubes that were not as advertised, buyer beware.

 

To the original poster. I seriously recommend you let Line 6 fix your amp as this is what I did.

My amp is not malfunctioning i only wanted to replace the tubes :).

The guys i bought the tubes from said that they consider 3mV difference very well matched tubes :(.

That's why i asked what are your guys opinions and experiances.

Im gonna experiment a bit with the original and JJ tubes to see if i can see a difference in sound and hum, i just wanted to see if it's dangerous to have 'unamatched' tubes in the amp, if it can lead to malfunctions.

[Brazzy 439]

My amp is not malfunctioning i only wanted to replace the tubes :).

The guys i bought the tubes from said that they consider 3mV difference very well matched tubes :(.

That's why i asked what are your guys opinions and experiances.

Im gonna experiment a bit with the original and JJ tubes to see if i can see a difference in sound and hum, i just wanted to see if it's dangerous to have 'unamatched' tubes in the amp, if it can lead to malfunctions.

 

Your right in that my amp must have been malfunctioning since I had some weird noise and pop and then intermittent sound loss. So when I put those new tubes in there that may have temporarily got things working but the real problem was still there.

 

Good Luck with your testing, If my memory serves me spaceatl has been using JJ tubes in his DT's for a long time now. I'm sticking with what Line 6 recommended since it works for me.

 

Try to let us know what you find out.

[psarkissian 316]

The guy you bought the tubes from might think +/- 3mV is fine

for matched pair tubes, but it's over the bias spec for DT50's.

 

I get too many DT50's across my bench that are blown because

of using JJ's, Mesa and the occasional Groove tube. Part of that

is incorrect biasing.

 

These aren't the same old tube amps we used to have in the

1960's and 70's. Can't get away with doing the same kinds of

tube swaps we used to do back then.

 

Best stick with the EH's and have it biased correctly by a Line 6

authorized service who will have the correct test and service info.