Mini Rectifier Tube Replacement

[e32lover]

Hi, I have been having some problems recently with my mini, when I power on, it will take a long time to warm up during which time it will crackle heaps. I think finally the tubes died, because I was playing it and over about 30 minutes i slowly lost most of the gain, and got some strange reverberations etc.

I have never changed the tubes on an amp before, but is it true the mini's are a DIY tube replacement, just plug and play?

Just have a couple of questions, how can I tell which tubes are stuffed? The amps is only a year old so would i start by replacing just the power tubes? And if so do I need to buy a matched pair? Or can I just replace one?

Also the tubes are stamped "Mesa Engineering" Do I have to buy mesa tubes or can I just get any brand of suitable tubes, if so what works well?

Im lost without my mesa, this thing is the best invention since the wheel.


Hmm, just had a quick look, these mesa jokers want $100 for a matched pair of mesa EL84 6bq5 tubes in Australia, when they are selling for 30 bucks in the USA! I can get a matched pair of JJ's for about 25 bucks, would they sound any different to the mesa's? I already paid 1700 bucks for my recto, now their trying to rip me with the tubes as well.

 

[bandit2013]

When it comes to power tubes, always replace them as a matched set. Stick with Mesa to keep your warranty in check.
I have a new Mark V, Original power tubes did not make it past 2 months. I did not opt for replacements from Mesa.
Since I do not have a mini Rec, all I can do is offer suggestion.

Depending on how long you had your mini, they tubes may be covered under warranty. (not sure how that applies outside of the USA). Easy way to find out which tube is the bad one, power up the amp, and play though it. Position the amp such that you can see the power tubes. The one that begins to glow bright red is the one needing replacement. (Large metal plates inside the tube will heat up red hot, not the heater filament that will always be orange in color). When the tubes are cold, does the amp sound better, and when it warms up it looses its character, power tube issue (usually). If it takes a while for sound to come out, that is may be a characteristic of cathode stripping (takes longer to generate the electron field which requires a longer heating time to boil off electrons). Sometimes associated with change in tone, typically flat in sound lacking high end.

I have been lurking in the Carvin Forums for a while, the V3M uses the same power tubes EL84. Many have switched from the PM tube to JJ and like the difference in tone. If you are considering JJ (eurotubes) I would check out their website, they may have a specific tube for fixed bias Mesa's. All of Mesa amp designs use a patented fixed bias circuit. With a fixed bias, you need to use tubes that meet the criteria used by Mesa. Eurotubes (JJ) should have something for your application. JJ tubes may be a good choice. Just keep in mind that all tubes even of the same model may not work well (depends on the distortion characteristic, i.e., early, mid, late).

 

[Addictedtokaos]

Loss of gain is most likely V1 or V2 (tube 1 or 2. look in your manual for numbering). Not the matched pair of EL84s.

its handy to have tubes you know are good before you start try and find the problematic tube(s). The preamp tubes are 12ax7s. and the power amp tubes are EL84s (do not confuse with EL34s).

First, If you dont have 2 or 3 new 12ax7s on hand I would order some, order 5 if you can afford them. Tubestore.com, Dougstubes, Tubedepot are all great places with fair prices to order from or If you go into your local guitar shop they should have some - what prices they sell for is anyone's guess.

Once you get some new tubes, take the cover off you mini.
See here http://www.youtube.com/watch?v=hO0AW0gZWo0

Next turn your amp on normally with speaker connected and start playing until you start to experience the symptoms. Once the issue starts happening, put your amp in standby (no need to turn off with preamp tubes) and swap V1 with one of the new (good) tubes. Take it of standby and try playing again. If the problem is gone then you found the tube. If its still there. Put the OLD V1 back in that you just took out and take the good tube and try it in V2. Keep going until using this swap method until you find the problem tube. Take some time to watch some videos on youtube on how to remove and insert preamp tubes if you havent done it before. The secret is to NEVER force anything. If it wont go, you dont have it lined up properly.


Another method of testing for faulty tubes is by having the volume up to a comfortable loud setting. Now start tapping/flicking the tubes starting a V1. Seehttp://www.youtube.com/watch?v=zb7HHi-Ryq8 and skip to 4:30. Doing this to the tubes one at a time should cause it to act up when flicked.

Just an FYI, Mesa currently uses JJ's in for 12ax7. They run some test on them as shown in the youtube link above and then stamp them as Mesa tubes. If you take some time to read here in the forums you will quickly realize there are many options for preamp tubes, not just JJs.

Good luck!