Avionic--
Are the capacitors your recommended a compromise between similar physical size along with increased capacitance rating?? That appears to be a pretty large bump in capacitance versus the originals, but you have likely done similar replacements with excellent results?? I also have a recently acquired MA5002. It's in working condition, but doesn't sound all that great. Maybe replacing the power supply capacitors would be a good place to start?? I suspect a number of electrolytics in the amp probably need replaced, but I have to set this aside for now. One other thing-- the channels are somewhat imbalanced when the gain controls are set to similar positions pretty much anywhere on the dial. Is this a common problem with this Soundcraftsmen amp?? Sorry for hi-jacking the thread. I will also do some further searching for this amp in other threads. I hope the OP gets his amp sorted out. Thanks. Jim :yes:
I need to take the blame credit for the selection of these caps.
When I needed to recap these in my original amp I researched hi and low for any info found one thread I believe.
These amps run class H so you have a low voltage power supply 63 v and a
high voltage supply 93 v this voltage varies by the demand using the circuitry Soundcraftsmen came up with hence vari proportion.
The low supply is used up to 125 - 150 watts it uses a 11,000uf 60v :scratch2: size is 2 x 4 1/2
The high supply kicks in as required +125 watts when the green lights come on in the MA5002 and it uses a 22,000uf 30v :scratch2::scratch2: size is 2 x 4.0
You maybe wondering how in the world a 93 volt power supply can use a 30v cap
The answer is the cap is connected to the 63v rail so the actual voltage potential is 30v.
The way these caps are mounted is that a bracket is used to hold the caps and it has a step in it to accommodate the 1/2 inch difference in height.
So researching what cap I would want with for this I determined that I needed caps
that had a max height of 4.5 inches and another that is 1/2 inch shorter and must be a max of 2 inch in diameter.
Well if you use a spacer under the shorter set of the caps you can use a cap of the same height.
Now why the selection I felt the originals uf ratings where marginal and the voltage ratings definitely where cutting it to close for comfort.
The rectifiers are 25 Amp so no worries on these being hurt by increased capacitance.
The amount of capacitance in a filter cap has a point of diminishing return but I look at as a rule of thumb 100 to 150 uf per watt so
150 * 100 = 15,000
150 * 150 = 22,500
250 * 100 = 25,000
250 * 250 = 37,500
I looked for 70 volt and up caps with a capacitance of 11,000 and up.
and 40 volt and up caps with a capacitance of 25,000 and up.
So are these uf values overkill ya somewhat but the size and the cost was the real determining factor.
The original voltages of these caps where marginal at best. So no way use 60v and 30v caps in these.
I guess the caps of the late 70s and 80s where a bit more forgiving on being run at the limits.
I have seen the EL caps with leakage so these are not so forgiving.
I also bypassed these using a Mallory film cap.
All I can say is the difference is not subtle.
FYI the caps used in the RA series are shorter but still have the size difference in height 3.5 and 3 inches EL caps
IMHO these are inferior to the caps in the MA5002 which used the white Sangamd caps.
Now regarding your issues.
I would be willing to bet the DC offset of your amp is in the range of 50mv or higher this will make the amp sound less than optimal.
This amp did not hit a home run with the circuit design around the diff pair.
Also the input caps need to be replace with a Muse NP.
Output variance couple of things the meter circuit could be a bit off or the gain pots could have a mismatch or the diff pairs are mismatched.
I have seen this also but after taking care of the dc offset and recapping the unit I just feed a test signal and set the higher gained channel down a bit.
The spec sheets from the factory on mine also show a bit of gain mismatch.
That is what the controls are for
IMHO a well running MA5002 is hard to beat.
