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[MarshallJMP]

I think that it is down to the most inportant variable, transconductance. Ra (Anode resistance) never changes much and gain is always consistent. It is true though that lots of the older tubes hold strong and seem to last a longer while in that regard.
[/quote]

ra and gm do change with the voltage applied to the anode,the lower the voltage the higher ra will be and the lower gm will be.But µ=gm x ra (or max gain of the tube) will stay relatively constant.But if you use higher voltages the output gain Vo/Vi will increase and Dtot (distortion) will drop.This with the same Ra resistor.Just to be clear Ra and ra are not the same,Ra is the anode resistor and ra is the dynamic output resistance which changes with the anode voltage.

[Harley Hexxe]

Hey Richard,

     No...I never spray tube sockets! I learned about that with all tube amps. It is possible I did get a pair of duds, after all, I did order those from Musicians Friend. The tubes I have in there now are a pair of long plate JJ's. They're alright, but not quite what I want out of this preamp. I got these tubes, and several others from Doug's Tubes. I did order two pairs of the RI Mullards, and put them in the MP-2's. I also got a pair of his pricey Penta 12AX7's and put them in the original MP-1. I may swap those with the JJ's just to see if they make any difference.

    Now, here is a question for MJMP that I can't recall seeing in any of the posts in the past: We all know that the stock MP-1 doesn't supply the filament with the full voltage, is this also the case with the MP-2 and the Classic?

    Harley

[MarshallJMP]

The MP-1 classic and MP-2 do get the proper filament voltage.

[Rusty]

Rock 'n Roll.   

   

[rnolan]

Hey Harley, it's definitely possible they were duds, it does happen, even when they've been well tested etc. If you like how they sounded in the Classic, I'd give them another go maybe from a different supplier ? Did they have any guarantee ? Not sure what Doug's return policy is. There's more than one story here about tubes being duds.
If for example a tube isn't pumped enough (maybe some issue when it was made ?) it will burn out faster as less good vacuum. This is one of the main reasons the old NOS tubes last so long as they pumped them for much longer back then.  From an amp manufactures perspective, they probably don't want them to last more than a year or two so you'll have to buy new ones from them.

Like light bulbs, they can make them so they last for a very long time by pumping them more (as required for lights on ships due to vibration), same with tubes.

[rabidgerry]

I've never had tubes burn out that fast.  I had a valvestate with a JJ in there for years and also a sovtek.  They were still working when I swapped them.

I'll see how long the bugeras last for.

I'll be doing some tube rolling soon (thanks to SC) so it's all about to get very confusing.  But we'll see how long some of them last.

[rnolan]

Hey RG tht will be good feedback 

[Harley Hexxe]

Hey Richard,

      The tubes from Musicians Friend only had a 30 day guarantee I think, which is pretty much standard these days if any warranty is offered with tubes at all. I'm not sure if Doug's has any warranty. Because of the fact that people have been dishonest in the past with tubes, shops that sell them here don't have any warranty at all. This is why I don't buy them from Guitar Center, or Sam Ash. Their policy is a "No Returns" policy once you take them out the door. This is why I'd have to take my tube tester with me if I bought any from those places.
     I'm probably going to try another pair of Mullards in the Classic when I get around to it, but I still plan to experiment with other tubes in there to see if I can get more of what I'm looking for out of it. The Penta tubes sound really good in the MP-1, but then again, so did the GT Mullard RI's that were in there originally. The MP-1 has more low end EQ than the Classic. so I don't expect to be able to match that no matter what tubes eventually end up in there. It might be worth the effort to experiment with some of the more High Fidelity tubes on the boutique market. I suppose it will still be a crap shoot as to how long they will last though.

    Harley

[MarshallJMP]

Ruby tubes have a warranty of 6 months.

[rnolan]

Hey Harley, My take on the boutique market is there are NOS tubes around (which also may/not be duds (statistically some will be duds)), NOS tubes buy you longer life (and sometimes better metallurgy, they all had their own specialist  metallurgy departments back then). Other wise the "character" of a 12AX7 is what it is, the different designs sound a bit different in various circuits. I wouldn't expect a NOS Mullard 12AX7 long plate to sound that different from the re-issue (if the re-issue is good), but I wouldn't expect it to last as long (pumping/vacuum).
But Hey. roll a few tubes and hear what makes the classic how "you" want it  , and then tell us (not that I've got a classic, LoL, wouldn't mind though).

[Systematic Chaos]

... I wouldn't expect a NOS Mullard 12AX7 long plate to sound that different from the re-issue (if the re-issue is good)...

Night and day difference, believe me!

[rnolan]

Hey SC, so why ? they are supposed to be a re-issue. So is the design the same ? glass thickness the same? metallurgy the same ? Well I've no idea but from what you are saying (night and day difference (and I do believe you  )), then things "must" have changed..  I do love the new sensor re-issue though, they are still a very nice tube, though now maybe I need to seek out some NOS tubes (at great expense.... well I could I spose)

[El Chiguete]

... I wouldn't expect a NOS Mullard 12AX7 long plate to sound that different from the re-issue (if the re-issue is good)...

Night and day difference, believe me!

Ok so now its your dutty to comment more on this! jeje. I only ask to make sure if you are saying that the older ones are way better than the newer re-issues that some of the guys here love so much and because of this I want to try them out soon.

[MarshallJMP]

I have to agree with SC,i think the only thing they have reissued is the name,but that's it.Many people think these are exact copies of the original but they are not,far from.

[DorsetRatt]

With regard to NOS tubes I found the following resource which may be of use, about halfway down the page ...

NOS TUBES?  The hype, myth, and reality
http://www.guitaramplifierblueprinting.com/pastinfo.html

Due to my limited knowledge of electronics the article explains things in terms I'm more familiar with ...

Gain => Horsepower
Output => Torque
Transconductance => Acceleration

Note: There is an obvious bias towards Groove Tubes on this web page