My periodic Mesa rant

[Leo_Gnardo]

had to open my big mouth!

Got a Mark IV, thought I was slick finding a shorted V2b orange coupling cap, but I was getting nothing from Channel 2.

Ugh oh, switching problem? Tons of Vactrols! Yikes!

Well, it was only V1b shorted orange coupling cap! Bad idea to use 400v ones.

Now I'm getting bias voltage slowly dropping to one pair of output tubes. Not the 220K feed, or the PI coupling caps.....THE BOARD is causing the problem!

Lifted the cap and feed resistor and wire to tube board and bias is solid as a rock! Now the other side is doing it too!

I've had a couple cases where highly regarded "orange drops" went bad in Mesa amps. No more can we say "can't possibly happen" because in amps 25 years old & beyond, it does.

Now leaky PC boards too? Yikes!

[drewl]

Yeah, orange drops rated at only 400v!

Due to the weird switching, it was passing signal on channel 1 & 3 with a shorted coupling cap, but not ch2.

[Leo_Gnardo]

Yeah, orange drops rated at only 400v!

Gotta save a buck when you're charging top dollar for your amps, y'know.

FWIW I don't even stock 400V film caps. 600/630V is what's in my parts bins.

[tedmich]

FYI I've been buying Kemet's R75L series caps lately, nice sounding little metallized PP units rated to 560VDC with long leads that are DIRT cheap; they only cost $0.23 and $0.29 respectively at Mouser for the 22nF and 47nF versions I commonly use.

not orange though...