Grail Tone ? Get bias for your Mesa !

[Big Harry]

Yes , after few years of tweaking with my RKII dual rec combo , my amp technician stop my agony and did the bias in a less than 30 minutes .
Guess what ? Amp was set so cold (factory) , hell cold , pulling only 45%-50% of available power .
That's way I've tried to sell this amp several times .
Now , after bias has been done , I finally know what Mesa Boogie tone looks like .
It looks like very good tone , almost Grail tone !
Tubes become so alive and kicking , clean channel is simply beautiful , 3th an 4th channel rocks ,
, channel 2 is simply wild !
So , find your self proper technician and do the bias .

Actually do your self favor , and in return you will have a brand new amp , 5 times better than factory set up one .
Good Luck !

 

[siggy14]

You can order tubes that will make the bias hotter, this is what I prefer to do then mod my amp.

Yes , after few years of tweaking with my RKII dual rec combo , my amp technician stop my agony and did the bias in a less than 30 minutes .
Guess what ? Amp was set so cold (factory) , hell cold , pulling only 45%-50% of available power .
That's way I've tried to sell this amp several times .
Now , after bias has been done , I finally know what Mesa Boogie tone looks like .
It looks like very good tone , almost Grail tone !
Tubes become so alive and kicking , clean channel is simply beautiful , 3th an 4th channel rocks ,
, channel 2 is simply wild !
So , find your self proper technician and do the bias .

Actually do your self favor , and in return you will have a brand new amp , 5 times better than factory set up one .
Good Luck !

 

[Big Harry]

You're right , that's what I have done already ,replaced original with JJ high gain tubes .

 

[domct203]

You're right , that's what I have done already ,replaced original with JJ high gain tubes .

Interesting, I've never heard of "High Gain" powertubes. Preamp tubes yes, but not powertubes.

You can order tubes that will make the bias hotter, this is what I prefer to do then mod my amp.

What siggy14 is refering to is selecting powertubes that are outside of Mesa specs that will draw more idle cathode current at Mesa's non-adjustable fixed bias voltage.

After having adjustable bias in my Roadster for some months now I have found that I like 6L6GC's biased in around 50% Max Plate Dissipation, EL34's around 55-60% MPD, and JJ E34L's around 60-65% MPD. Any more than that is really pushing the Power Transformer beyond it's design specs IMO. YMMV.

Right now the Roadster is with my tech for Mercury Magnetics Transformer upgrades so I can properly run 6550/KT-88's. I am working with MM to design an upgrade Power Transformer for the Roadster that will allow me to run just about any Octal Socket Power Pentode!

Dom

 

[Big Harry]

That's good info , thanks .

 

[Pig Muffin]

if i wanted to have the bias mod done to my series 2 rectoverb head.....what the typical cost to have something like this done?

 

[domct203]

if i wanted to have the bias mod done to my series 2 rectoverb head.....what the typical cost to have something like this done?

My guess is somewhere in the $75-$150 range.

BTW- this will void your warrenty.

DO NOT attempt this yourself unless you are educated on working with tube amps. There are LETHAL voltages stored inside the amp, sometimes for days after being unplugged.

Dom

 

[Pig Muffin]

found a shop in cincy, chrome dome, that will do it for 50 bucks.....taking it after practice tonight. Hopfully my little 50 watter will sound a little better. prolly not but hell with it. lol.

thanks for the advice.

 

[domct203]

Make sure you educate yourself on setting tube bias. You can't just go aimlessly adjusting powertube bias...... Run too hot and you'll blow your powertubes, possibly taking out components in the amp. You will need a bias probe to measure idle cathode current as well as plate voltage to make accurate calculations.

Be careful, the B+ (plate) voltage in your amp is upwards to 480V, enough to stop your heart.

A quality bias probe makes these measurements both safe and easy.

Dom

 

[Pig Muffin]

i am going to have the guys at the shop do all of the work and set the bias to my EL-34's. Is there a percentage of plate dissipation i should have them set el-34's to?

 

[Pig Muffin]

basically, I dont want to touch anything, just tell them where to set it and take it home and play it.

 

[domct203]

The correct bias point of specific powertubes is set using a sine wave generator and scope to match the operational point of the amp.

But.....

General rule of thumb is to never exceed 70% of max plate dissipation. IME I like EL-34's around 55-60% max. YMMV as everyone has a different opinion of what sounds best to them. IMO Rectifiers sound best for Modern mode with a clean output section. The hotter you bias the quicker the powertubes will exceed that clean output and begin to distort.

Just keep an eye on the tubes to make sure they do not redplate while playing.

Dom

 

[Pig Muffin]

Ok, so I will tell the dude doing the work to set the plate level at like 60%, I will also keep an eye on the tubes to make sure they aren’t going haywire, do the tubes still have a chance of redplating at under 70% max? If so I will tell the guy to dial it in a 65% and keep an eye on them to make sure. If I stay under 70% then redplating the tubes shouldn’t be an issue right?

Thanks for chatting pretty much all day with me on this, you have been uber informative bro!

 

[domct203]

No prob, glad to help.

It really depends on the quality of the tube. Another thing to note is fluctuation in the supply (wall) voltage. The reason I bought a voltage regulator for my rig is due to seeing a voltage range of 110V-122V across the places I had been playing. That could be a difference of almost 50V at the powertube plates. This could change that % of Max Plate Dissipation into redplate territory if you are already close to 70%. If you choose to get up to 65% yes, keep an eye on those tubes.

I'm not trying to scare you, I just want you to be informed. I know guys who bias their amps at 70-75% and never have issues. I just wouldn't take that risk with my 2K amp.

Dom

 

[Pig Muffin]

i know the term is called redplating but what does it look like? I am assuming the bottom of the tube starts glowing red?

 

[domct203]

The internal structure of the tube that you can see, the grey colored box like structure, is the plate. It will glow cherry-red, like the coils on an electric stove or heater, hence the term red-plating.

Here is a example of the plates starting to glow:
http://lib.store.yahoo.net/lib/thetubestore/redglow.jpg

It's pretty much the death of the tube if it runs away and the whole plate glows, followed by the amps fuse hopefully.

Dom

 

[shytfayse]

Balls! That's just when the amp starts sounding really cool!