Mesa boogie 50/50

[kurtdaniel]

ive seen a thread about a Bias mod on a 50/50.. here it is.. The Boogie Board • View topic - Bias mod on a 50/50 : how to do.. this will surely improve our amps performance and how we are playing guitar..

[kurtdaniel]

orayt!! tnx..

[Jazz P Bass]

Sure.
But start a new thread.

[kurtdaniel]

ive seen a thread about a Bias mod on a 50/50.. but its on another forum.. can i post the link here?

[steelhorse]

How would you bias a Boogie amp? I have a buddy who has one and he doesn't care for the tone and I suggested re-tubing and checking the bias then I remembered as a former MKIII owner I never did bias but I did always use MB tubes.

[stokes]

A lot of tube suppliers are selling tubes that are tested and graded to fit Mesa's bias range.GT has been doing it for years,in fact Mesa endorses the use of GT's.I have heard that Eurotubes and KCA are doing the same.I would have to think or at least hope the Mesa techs you mentioned are using tubes that fall into the peoper range,in which case you would be safe.I think you can attain better performance out of your tubes if you fine tune the bias.Even if I were inclined to use the Mesa system I would still have to check the bias to see where they were idling,which would just force me to tweak it anyway.

[jak0lantern01]

In light of the statement everyone is complaining about, shouldn't there really be more issues with Mesa amps? I mean, is everyone really using THEIR tubes or throwing non-Mesa tubes without properly adjusting the bias? Something just doesn't add up here. Plus, there is the reality that two authorized Mesa techs told me don't bother with Mesa tubes, it's all about the name and that's it. As I stated earlier, the non-Mesa tubes they tossed in sound great and haven't yet experienced trouble. Since we're on the subject of tubes, I wanted to get an opinion on how many hours people run their tubes before replacing (Pre and power). I'm sure you're not all waiting for failures before swapping. I average anywhere from 6-8 hours a week at jam-level volumes (I have to hear over the drums and everyone else).

[stokes]

Yeah, he should have said a lot of things.Mostly he should have kept his mouth shut.I cant believe someone with his background would make some of the statements he made in that paper."Clearly this is something most repair techs should not attempt".That is absolutely absurd.This "paper" was obviously directed towards people who have no idea what goes on in their amps,and scare them into using his tubes and putting amp techs out of business.

[Steve Conner]

Be that as it may, when the original bias voltage is altered far enough, it will compensate for the tube's abnormal performance and the correct amount of idle current flow may then be restored. Clearly this is something most repair techs should not attempt.

Surely Randall Smith meant to say "There's nothing better than an amp with permanently installed cathode resistors brought out to jacks on the chassis for plugging in a voltmeter, and a bias pot for each power tube with a wide range of adjustment too, so you can stick in any old tubes you found at a flea market and let them rip"

[Tom Phillips]

Pre-amp tubes don't require a bias adjustment if that's what you are asking.
Just use tubes that sound good to you.
Due to the high gain MB circuit you will need to use good tubes that are low in microphonics in the the front end of the pre-amp.

[jak0lantern01]

What about pre-amp tubes?

[stokes]

As long as your plates arent glowing red or orange you are safe.Dont confuse the normal glow of the heaters with a red plate.The plate is the large gray structure in the tube,it will look like someone hit it with a blow torch if it is running too hot.If it is have the bias set properly or the tube will fry,and may take other components with it.Groove Tubes can safely be used in a Mesa if they are in the #4 to 7 range.If that is what they put in there you should be okay.I dont care for this system,but it is safe.Like Drewl, I like to set the bias for what I think is the best performance.

[Tom Phillips]

My current approach to MB tube replacement:

I keep tubes in stock with a decent range of pre-tested and graded bias requirements. I can then select a set that works as well (or better) than the Mesa tubes. I still check the bias and make any required repairs, such as replacing burnt screen & hum balance resistors, before I button the amp up. This is the best solution for me and the customer. This doen't take me any more time because all my customers want the amp bench checked anyway. Sometimes they buy an additional spare set of tubes matched to those I install.
Customer gets a properly biased amp. No circuit mods required so no-one can ever complain that I voided their warranty, screwed up their amp, reduced the resale value etc.

Customers have brought in MB tubes. They don't all fit in a narrow bias range. See my earlier comments about the color coding.

Tom

[jak0lantern01]

But that's my point, or perhaps I wasn't clear enough. It was indicated that I didn't have to worry about the biasing. That's the part that scares me in their statements. These are the guys who fixed my amp. They didn't replace the tubes with Mesa's, and they sure as all hell didn't do anything to alter the bias. This leads me to a question: what are the negative effects of installing tubes without correctly setting the bias? I do have to admit, the EL34's they installed for me sound damn good, though.

[drewl]

You're wasting $$$ because Mesa charges alot for tubes.
You CAN use any brand, but as stated here they need to be biased.

Some people change tires and randomly inflate them without checking tire pressure, but we all know a properly inflated tire will last longer, perform better and safer....same with properly biased tubes.