Rabies,
I use to be just like you, crazy over the bias thing, jumping from Amp to Amp always in search of the next best thing. What I found out of all the amps was mesa was my thing, second thing I learned is ditch the crap *** tubes any company ships with there amps, unless they are shipping good stuff.
Here is what I have learned about the bias thing, first off with an amp that makes mostly pre-amp distortion, you actually want the power section to be cold, not super cold and I will admit with stock mesa tubes it will be super cold, however they have changed that in the last two years since people were complaining and jumping ship to tubes from other tube companies. This has been confirmed by Trace at voodoo amps about the bias being hotter now.
But the reason you want the power section to be cold is, alot of preamp distortion+power distortion=mush.
Now if you are planning on keeping the gain way down on any of your amps, and I dont mean half way down, i mean down to the point that it makes just as much as say a Marshall Plexi without power tube distortion, then yes you want to get your bias hot so you get that power amp distortion cranking as well. Now since you listen to metal, I am gonna take it you like the preamp distortion.
Even Bogner backs this up, he may not tell you directly, but typical EL34 bias should be 35 to 40, however read the uberschall manual and it tells you flat out, bias it around 25 +/- 3, so anywhere from 22 to 28 and that is considered cold.
Mesa Ships usually with a bias of about 19 to 24, however range on 6L6's is 30 to 35, so has you can see there is really no difference between the Mesa fixed Bias and the Uberschall adjustible bias when you go by the manfactors instructions.
Now to VHT, Diezel, Engl, etc. honestly yeah they sound tight as hell with gobs of distortion, however they just have this solid statish vibe to them. yeah they are still warm, but not as warm as a mesa. However they are passible and good amps, just not warm enough for me.
Bogners are the only other high gain amps that i feel are warm enough that I have personaly played or heard live, I had the uberschall great amp, however very dark amp, by cranking the mid's or I should say the presense I could get it close to the recto, but it still was not a recto!
As to the Rivera I have never played any of there high gain stuff, but I have heard good stuff about them, but then again it is usually from the people that play diezels and ENGL's etc...
As to Slipknot, Tool and you saying good things about these amps. You I dont know that well, but I have seen your postings and I am gonna take it you are early to mid 20's still trying to find your tone and letting peoples opinions sway you to much without actuall faqs to back it up.
Slipknot, well lets just says they are whores, they will endorse anything if they get paid enough. Best slipknot tone, first album, James Root into Mesa DC10 and Mick used a Marshall JMP-1 into a mesa 2/90 power amp.
Tool, you can not judge his tone by the Diezel alone, last I heard he is still mixing amps together, more then likley if he is using that marshall still, well that is were his warmth comes from.
Bias mod, here is my take on it, like I said I was like you, went crazy about it for awhile, but then did research and found out you want that bias cold on a high preamp gain beast.
If you want to bring the bias up on a mesa amp, Order yourself any tube brand you want, tell them it is going in a rectifier, mark or whatever amp you have and tell them you need something to bring the bias up a little warmer.
Any good tube dealer should know the spec's of mesa's and give you the right tube to help the bias out. I know the tube store does, Eurotubes does, the tube depot etc..
As to your JMP-1 going into the mesa and squealing etc.. Honestly dude the amp is not made for that, do yourself a favor, go pick up a used Mesa 50/50, the older ones that only took 6l6'S can usualy be purchased used anywhere from $400 to $500. Order some tubes from a good tube company and tell them you want to get the bias a little warmer in it and you will be set.
I am also not biased just towards mesa, it is my main sound, however I do have some JCM800's sitting in my room, I love the peavey 5150's for a different style of music and I have a bogner XTC in my room. But my main stays are mesa and the amp I always go back to.
rabies said:
all Randall momma has to do is introduce adjustable bias trim pots like all the other brands and I'll stop complaining.
they've brainwashed everyone into thinking it's "easier" to switch out power tubes and just flip a switch but it's also "easier" to have crap tone as the bias ranges on EL34's and 6L6's are different. ask stokes if you don't believe me.
honestly, how hard is it to bias an amp that has external bias points like the Marshall TSL100, Randalls or newer Diezels?
Einstein (Herberts notes in brackets) has external bias points and its trimmer is accesable from the top
http://diezel.typo3.inpublica.de/tech-corner.3.0.html
The MTS amplifiers are designed to accept a variety of different tube types. EL34, 6L6, 5881, 6CA7 and 6550 are among the possible choices.
http://www.randallamplifiers.com/about/warranty/manuals/RM100manual.pdf