Mesa Heartbreaker 12v power supply capacitor question

[MichaelNuzum]

I have a mid-90's Mesa Heartbreaker getting a full recap, and I have a question about one capacitor in the 12 volt supply for the footswitch. On the schematic, it shows two capacitors, and the only value shown is 1kuf@25V. On the board are two caps, the second one after the 100 Ohm resistor is the 1Kuf value, the first cap closer to the transformer is 150uf@100V. Interesting thing is the board has silkscreened identifiers and the slot is labelled 150uf@100V.

Has anyone seen this before? Is this a misprint at the factory? It just seems odd to drop the capacitance by almost a factor of ten, and at the same time spec'ing a 100V cap for a 12V system. Something seems off there. Should I trust the schematic, or what came stuffed and silkscreened on the board? (The current owner acquired the amp "blown up" so nobody knows if the system worked correctly when the amp was previously functioning.)

Similar but somewhat unrelated question, same amp, same schematic page, in the filament supply section. The schematic calls for a whole bunch of 6.8K@10V capacitors. The amp came with 6.8K@6.3 V caps. Now, doesn't a cap going across from +3V to -3V see 6V in operating range? Wouldn't that mean that under no stress normal operating conditions those caps are being run at nearly full rating? Or am I not doing the math right?

Many thanks in advance to anyone who can shed a little light on this for me.

The schematic is attached. The power supply is on page 8. I apologize for the extra pages.

[The Dude]

I would go by the silkscreen values on the footswitch supply caps. 1,000uf should be plenty of filtering for the FS supply. That said, i have no idea why they used a 100V cap there. Maybe they got a deal on them or had stock they needed to use up? If you don't have a 100V cap handy, measure the voltage there and use a cap that's rated higher. On the filament supply caps, I'd definitely use at least 10V caps there. If you're going through the trouble to change them, you might as well make it more reliable.

[MichaelNuzum]

Hey Dude, thanks. I worried about using the silkscreened value as it is only 150uf when the schematic shows the 1000uf value there. That's the part that has me scratching my head. I didn't know if that meant the designation for the 150uf cap was missing from the schematic, or if they were both originally rated 1000uf and the one got changed before they printed the pcb. The 100V rating just made it even a little stranger.

And yeah, I went ahead and ordered 10V for the filament supply. 6.3 volt rated caps just seem too small.

[g1]

mesa schematics are ok for general overview, but never rely on them if they disagree with the amp in front of you. In those cases, ask the factory for details or a schematic by serial #.

[DrGonz78]

Could they have had the pleasure of SGM being the one in charge of schematics over there at Mesa? I could just see him making a few minor adjustments to the schematic that are guaranteed to kick some ass.