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Modification for Mesa Boogie .50 Caliber

1/1/2000 11:56 AM
Modification for Mesa Boogie .50 Caliber
Hi Guys  
First of all, best wishes for 2000!  
Does anyone know of mods that can be done to improve the lead sound of a Mesa/Boogie .50 Caliber with EL84 powertubes? It's got a very buzzy extremly saturated sound, not at all appealing.  
I want it to sound warm and tight and less saturated I've contacted several amp-customizers but all of them say it's virtual impossible to alter it. (Boogie's seem to be difficult to customize generally!) I don't mind sacreficing some tone in the clean mode. Can anybody out there help me, it's driving me mad!  
I have the official drawings for this amp from Mesa/Boogie.  
1/2/2000 10:46 PM

I have used a .50 cal for gigging for the last 10 years. Mine has the 6l6 output section. How loud are you using the amp? The louder you set it, the smoother/warmer the tone gets. Mine sounds amazing on 6 and higher. The tone gets buzzier at lower settings. This is not the amp to use in your livingroom, it was designed for club use. Are you using an extension cab? Try a Mesa theile cab if you find one. What preamp/power amp tubes are you using? I'm using the GT 7025 (JJ Tesla)currently in the preamp. The Sovtek 12ax7LPS is also nice. Mark
1/3/2000 7:07 AM
Gene F 6L6 M/B .50 Cal
I second that opinion - the 6L6 .50 cal is a loud and smooth gigging amp, good for playing clean-to-dirty funk, blues, R&B, jazz. This amp reminds me of a good loud Fender tone more than anything. But this ain't the amp for your ultra-saturated "Santana" Boogie sound...
1/3/2000 8:33 PM
Re: Modification for Mesa Boogie .50 Caliber
Thanks for your sugestion, but i'm aware that all amps  
sound at their best when crancked up.  
The "buzzy" sound i refer to is also present when crancked up.  
I have tried all kinds of tubes and it has already cost me an  
arm and a leg doing so.  
There are five 12AX7A Mesa tubes installed at the moment and  
four Groove tubes EL-84S (6BQ5) powertubes, bias rating #5.  
The .50 Caliber you had was probably a .50 Caliber+ which  
indeed uses 6L6 powertubes and has a lead master pot,and sounds very different from my version (i've A/B tested this!)  
However the preamp-section should be virtualy the same.  
I have tried it with an extention cabinet.  
I should mention that it is extremly sensitive when any effects-unit  
(Rocktron, Lexicon it doesn't matter)is connected in the send en return-  
jacks and overloads quickly and is therefore practicly unusable.  
Maybe there is something wrong here, but i don't know how i can check  
it for tolerable values (voltage, dB's).  
It has always been this way but i never cared for amp overdrive or effects before.  
If somebody has got some sugestions i'll be glad to here of them.  
Regards Andy
1/3/2000 10:10 PM

Right, mine is the .50+. I also have a .22 cal that uses the el84, has a similar preamp structure, yet sounds pretty good esp. when cranked up. My .22 doesn't have the EQ which is very necessary in these amps. Does your amp have the EQ? The .50+ has "auto select" which allows using the eq for overdrive only, if desired. This is how I run mine. Anything I use in my effects loop needs to be trimmed down quite a bit. I use an Alesis Midverb3 with input/output volume controls and it matches up nicely. You have some good tubes there so that can't be the problem. I used a 12AY7 a few times and this did tame that "high gain" sound  
a lot. The headroom in the clean channel suffered too much though to use all the time though. If your schematic does not show the voltages on the output tubes(it should) call Mesa and ask for them. It is possible that some resistors have gone out of spec. When my amps hit the 10 year old mark, the carbon comps had drifted in a few areas. In fact, one resistor in the .50+ is designed to burn/melt down during use! They have been great to me when I have needed tech help. Good luck, Mark
1/4/2000 8:12 PM

Thanks Mark.  
i agree, the equalizer is indeed necessary for controling  
the lead sound, mine has one too.  
I think i'll try that 12AY7 thing you mentioned (if i can  
get one overhere!)  
I've already measured all the voltages in the amp according  
to the schematic.  
I even contacted Boogie regarding some readings which i didn't trust.  
But these also turned out to be within tolerance.  
Indeed Boogie's technical service is great but only goes as far as a  
certain point,i believe my problem goes bejond that point.  
I even had this amp serviced by the local Boogie repair-centre,  
but they don't seem to care much and it sounds oke' to them.  
I know it's not!  
I also had a local amp goeroe take a look at it and he immediatly detected  
the bad sound, however he suggests to rewire the whole thing and i do not  
consider this an option as i like to keep it as original as possible.  
So the only way to solve this is to do it myself in some way.  
1/5/2000 1:19 AM

You may be right. Esp. since you have had a tech go over it. Maybe try R.G.'s tube amp debug for some ideas. You can also check that all the wiring to the pots/switches is done correctly or not cold jointed. I just thought of something. Try sending the preamp signal out to a different amp. Then try sending a signal into just the .50 power amp section. This might help locate which area the trouble is in, and save some time. The last resort may be to just go through the amp from the input jack, through the entire circuit. This will be a time consuming task. Let us know how you make out. Mark
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