MK 2C+ Class A question

[Henz]

You got the idea. The plates may be sitting at 350V WRT ground at idle, and the bias might be -60V on the other side so the voltage across the cap would be 350 - (-60) = 410V at idle. Then during transients you’ll see an additional 60V across the cap if you’re running at full power.

The film foil technology doesn’t help you here either, once the electric field breaks down the dielectric in even a tiny place you’re hosed. Metallized film caps have a self healing property where they can tolerate small areas that were broke down by the electric field

Ty for the advice with the upmost respect from you two. This is the first time, I think, that I ever heard about upgrading the the 30uf. Besides the obvious failing sign, bulging, what are the other symptoms as to which you describe? Thanks? Jim

 

[user 41014]

Ty for the advice with the upmost respect from you two. This is the first time, I think, that I ever heard about upgrading the the 30uf. Besides the obvious failing sign, bulging, what are the other symptoms as to which you describe? Thanks? Jim

It is an over voltage condition that does not effect the other two 30uF that see stepped down volts.

I did wonder if this only applied to the coli but this is the most common filter I see go visibly bad (bulging) and that goes back to my 100/60W 76 boogie.

In 1985ish dual 40uF caps were used, one underneath the PS board but 47uF is a standard and here is a mb draw up to replace the 1st filter. This gives 700V protection.

 

[Henz]

It is an over voltage condition that does not effect the other two 30uF that see stepped down volts.

I did wonder if this only applied to the coli but this is the most common filter I see go visibly bad (bulging) and that goes back to my 100/60W 76 boogie.

In 1985ish dual 40uF caps were used, one underneath the PS board but 47uF is a standard and here is a mb draw up to replace the 1st filter. This gives 700V protection.

Back when Randall, Mike and Doug were tweaking the idea of a C+, what % of plate dissipation were they shooting for with the 105 PT? I read in different threads here that Mesa biases amps on the cool side as opposed to the " nominal " 70%.

 

[user 41014]

Back when Randall, Mike and Doug were tweaking the idea of a C+, what % of plate dissipation were they shooting for with the 105 PT? I read in different threads here that Mesa biases amps on the cool side as opposed to the " nominal " 70%.

That is a good Q for mb. I just got my 1st 105 a couple weeks ago.
For class AB, my take is much much lower on any PT. Less than 50% I think puts you in the playing field.