No schematics, here is the info I have.
First check the serialnumber of your unit!
Up until now i´ve recieved comments of some users with sr.nrs. below FP-000400 to be in a somewhat different state and can look pretty messy, with components soldered even in mid air!
Mesa clearly did some hasty last-minute modifications to these units.
However, they assured me that the circuitry is the same as the later "Standard" Formula´s!
On these units i would recommend to only try replacing the resistor first as this might be enough for you without too much hassle.
That said you can read on:
Be save when you work inside your amp!
There can be lethal voltages present even when the unit has been off for a while.
If you don't know which precautions to take poke around the Internet, there's lot's of information about this.
All the mods are to be done at the tube-printboard.
I did try several other things at the main-printboard but with no significant results.
Using common sense and care is required, don't force things!
I do not take any responsability regarding this mod, you do this at your own risk!
There is something you should check for in your Formula first, at the tube-printboard:
-Check if there's a .01uF (.01K) capacitor placed instead of a .047uF (.047K) near the
middle relay (#5) at the tubeboard (see Fig. 1)
If not: replace for the .01uF(500-600 Volts), use a Sprague "orange drop" or preferably a
Xicon Polypropylene capacitor (Boogie uses these too)
Chances are there is already a .01uF in there, mine did not!
I placed mine at the back of the printboard since there is little space left over, my old
capacitor was damaged by one of the nylon studs which hold the printboard.
-Replace the 475Kohm grid load resistor (colorcoded: yellow,purple,green,red )of the first
lead gain stage for a 1 Megaohm 0,5 Watt (or 0,33 Watt) resistor (See Fig. 1)
-Replace the cathode bypass capacitor for this same stage from 1 uF to .47 uF (See Fig. 1)
use a Sprague/Vishay 173D 35Volt tantalum capacitor for replacement, to preserve the Boogie layout.
You could use an ordinary electrolytic too but this could sound differently.
Make sure to place the capacitor in the right direction (+ or -)
