MT15 power tube question

[PB26]

Looking to pick up a used MT15 locally and its a version 1 with 6L6 tubes. I know there was a switch to 5881 at some point but I'm wondering:
-Is it the same amp apart from the new tubes, or did they tweak the guts of the amp for version 2?
-If I throw 5881s in there what is the bias value I need? I know the manual says 30 but is that for 6L6 or both 6L6 and 5881?

Thanks!

 

[Toolmaster Of Brainerd]

I don't know, but try emailing PRS customer support. They're usually pretty helpful.

 

[andy474x]

There have been some changes to the circuit along the the way, but not for the purpose of accommodating the different power tubes I believe, you should be able to swap out the 6L6's for 5881's with a bias adjustment.

That being said, and especially given the limited tube supply right now, I wouldn't worry about swapping them, I doubt you'll hear much difference. I have one with each and can't tell.

 

[Bogner]

If it sounds and feels good when you play it I would leave it alone and keep it as is until you have to change tubes.

 

[Goran Lorencin]

With the power tube swap you "change" the slight final tone nuance the amp can offer, for example my original 6L6GCs are sort of more "ruff/visceral/growly" sounding, and when I put in the TAD 6L6GCs (different/taller tube with the getter on the top, Rubys have it on the side) it becomes grainier/tighter, kinda bit more "British" if that is a thing. The difference is not night and day, but enough that you can feel the difference when you play. The 5881s are said to be a bit more powerful than the 6L6s, have not tried them yet, as I am quite satisfied with what I have making my sound. But the fun part is, if you have a bit of time&money and a purpose behind the act, you can really explore the sounds with swapping preamp and power tubes ... there are many, many, many, many possibilities as Commandant Lassard would put it

 

[jak3af3r]

The real question here is what plate voltages are they running to get two 6L6s down to "15 Watts?"

 

[Wyzard]

The 5881s are said to be a bit more powerful than the 6L6s

If we're talking about 6L6GCs, then it's the other way round. 5881s break up earlier and produce a bit less power.

 

[Goran Lorencin]

If we're talking about 6L6GCs, then it's the other way round. 5881s break up earlier and produce a bit less power.

Thanks for the correction, I think I read somewhere that they have a slightly higher wattage and break up later. Well, there you go, when learning from the internet and not checking facts.

 

[Wyzard]

Yes, the 5881 gives around 15-20 percent less output at full welly than a properly driven 6L6GC.

The 5881's alter-ego (i.e. same spec) is a 6L6WGB, just to further confuse matters.