Use of non-Mesa tubes

[bgh]

I have a Mark-IV that was tubed with Eurotubes (2 EL34s and 2 6L6s). A while back I found a quartet of EL34s and one of 6L6s on sale - so I bought them. This was before I understood Mesa's used of fixed bias. I have no idea if either set is 'approved' for Mark-IV use. I now know that you are not supposed to use tubes that have not been tested for complicity with Mesa's biasing.

All of that said, I have 3 questions:

1. What would happen if I did uses some tubes that did not match the range specified by Mesa? If they were too cold, would the amp simply sound bad? If they ran too hot, would it harm the amp?

2. What sort of outfit could I take the tubes to in order to find out if I could safely use them in my Mark IV?

3. Are all Mesa's biased the same? Would 2 EL34s for my Mark IV work in say a Stiletto Ace?

Thanks in advance for your input.

 

[Audiokill]

1. Power tubes that are out of Mesa's specs will not harm your amp, but your tone may suffer. Cold tubes will sound too clean. Tubes running too hot will sound overly distorted and won't last long. Eddie Van Halen used to bias his stock Marshall head so hot that his tubes would fry within a couple weeks, but it was his true secret ingredient to achieving his legendary "brown sound" (Eddie never modded his Marshalls. That was disinformation spread by the band at the time to protect their Golden Goose). However, doing this to a Mesa will not sound good.

2. I've been wondering the same thing.

3. Any pair of Mesa branded power tubes will work fine in any Mesa amp, provided you aren't mixing up your 6l6s and el34s. All Mesa tubes of the same type are not quite identical, however. Some run slightly hotter than others, but all are within spec for your amp. Mesa rates tube bias by a color code system that looks like this;

White - hottest
Blue
Gray
Green
Yellow
Red - coldest

You'll find the color identification printed on a sticker on the base of any current Mesa power tube. With that said, don't go wasting your money buying up all the colors in an effort to see which ones you like best. You will probably hear very little or no difference in tone between colors. The color coding is only there to help you avoid mismatching your tubes.

Waste your money on a pair of Str-415's, instead. I'm jonesing for a couple of these bad boys right now. :twisted:

 

[Don]

1. Using tubes outside of Mesa's specs can harm the tubes and your amp.

2. I think anyone with a tube tested could compare the tubes to tubes that are within Mesa's spec.

3. Mesa amps using the same types of tubes are biased to use the same tubes as each other.

 

[bgh]

Thanks for the answers, guys.

The answer to #1 still eludes me - one response is 'yes' and one response is 'no'.

 

[daviedog]

Under biased...will red plate, hum,& finally blow a fuse.
Over biased...distorted weak.
The bias is determined(required) by the tube, not the amplifier. A well designed amp will have a bias supply to support the tubes installed.
No problem in the 60's with western manufactured tubes, hense, fixed bias supply for output tubes.
Today tube q/c questionable. Randy's trying to address that issue with tube inspections.
In 30yrs of playing mesa amps, I've never bought mesa tubes. I love my boogies and would not put them in harms way!!
Today's tubes are also handled with trim pots, but that is still a Fixed bias amp. You are just re-engineering it.

 

[HBob]

You need to know how your amp shipped. Mine uses a pair of red tubes and a pair of green tubes. I got tubes from eurotubes.com and they knew what tubes to send me based on which tubes came with the amp. You could maybe take your amp to an authorized repair shop and they could tell you. They could also see if your tubes fall within the ranges of the color coding that Mesa uses. Or maybe see if Mesa keeps records by the serial number of your amp. Then when you find out which color tubes go with your amp you can order new ones from someone like eurotubes. Bob at eurotubes loves the MK IV and has years of experience with that amp. He can tailor a set of tubes to make your amp do more of what you want and less of what you don't want.

 

[swbo101]

TudeDepot.com is very good, I trust them and have been buying tubes there for my Mark IV for years. They'll set you up.

 

[Whoopysnorp]

I think it's fairly unlikely that you will harm your amp by using non-Mesa tubes in it. There is a chance that you could get a set of tubes that runs too hot in that amp, which could lead to the tube failing, but your fuse SHOULD blow before any damage is done to the amp. I think it would take a pretty extreme mismatch to make this happen.

If you have a bias probe, you can easily test how well-suited your tubes are to your amp just by doing the usual measurements and seeing where they sit. If you don't have a bias probe and a digital multimeter, I'd suggest investing in one.

 

[daviedog]

Good point whoopy.
I bought a pair of bias probes from Hoffman Amplification for 17 bucks. You have to solder to assemble. Less than an hours work.
Before buying valves, GET RETURN privilege. Valves should be to 'spec' or they shouldn't be on the market..