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McIntosh - Hints and Kinks

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I am recapping my MC2125. I cannot find or decide I guess what caps to put in the power supply. The main caps are the silver Mepco/Electra 10000uf, 50 VDC.
This is my first recap, and I wanted to change these since the amp is 31 yrs old.
Would appreciate any suggestions / sources for these big power supply caps.

added note:
I did find caps that are exactly the same size, including the spacing for the screw mounts at Mouser. However it is not available in the 10,000 uf. The new one is a Vishay/Sprague 15,000 at 50 V. I was worried about getting caried away with inrush or charging peaks since it is going to up the capacity about 50% at the output of the bridge.

Thanks
 
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You are safe up to 20,000uF or more, the 2125 has inrush limiters to protect the bridge and power transformer.
 
Hi I just got a C35 and MC2255. They seem to be running pretty good for their age. What kind of maintence should be done at this point? The 2255 seems to have a meter thats a little low and slow. Is it in need of cleaning or is there a deeper problem?
 
Meters calibrated, controls cleaned, a good coat of polish, and a full test to specs are what is needed, from this the next step would be decided.
The next step would be a freshening up with some capacitors in the audio path, might smooth things out some, at this age it's a tossup as to how much to do and how much it will help.
 
Hi Terry,
Im alittle embarrassed I didnt question this sooner,
As Ive had this MC 2505 amp for over 4 months now ....

Should the "Red" light above the Mcintosh logo stay "ON"
during entire operation ???
(I hope so~)
Thanks - Mark
 
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Same lights that do the lettering for the controls do the red indicator indicating power ON, yes it stays on if power is on..
 
Terry,

I finished recapping my MC2125, everything looks ok at first check. Bias adjusts OK, etc. I thought I had read on here that all 4 lights (two normal and two red limits) come on briefly when you power up. Actually the normals stay on if I think a second.
Should the limits blink? The pwr circuit was toast at first but new small caps and diodes in the front board fixed that.

Thanks for any info.
 
This is a hard to answer question, the circuit as not specifically designed to blink the limit lamps then go to normal on, but most PG amplifiers do this when turned on from a cold start, good way to check the limit lamps.
 
Just letting you know what I found with my limit lamps......I shouldn't even tell this one....I did a little troubleshooting, found that pwr guard was working well on the output if I pushed it too hard with a sig generator. When it was limiting the clipping, nothing seemed to be driving the lamps. I had put a piece of scotch tape on a couple of pins on the single sided edge on the pc card while isolating circuits at early troubleshooting . After letting the project sit several months, guess I forgot I had done that, so the tape was doing its job- blocking the limit drive inputs on the pwr supply board!
Unit puts out 180 w/pc before noticing clipping on the output. The pwr guard when switched back on, lights up at almost the same pwr out. So I guess it is working OK.

Just for the record, my red limits do not come on at power up on this particular unit, but they work fine now that I found my goof up.
 
NOOB Question: Acquired a MC2100 with screw sheared off in the common post on the left barrier strip. Are there any tricks or pitfalls associated with changing the strip?
 
Just unwrap the soldered wires one at a time, install new barrier strip and solder posts from the old one, re-solder wires from the old one. If you get confused on which wire goes to what terminal check the other as the color codes should be the same.
 
Terry,

Finally got the barrier strip changed, cleaned and waxed the amp and got it playing again. I sounds great, no distortion, but, the second heatsink from front is running quite hot. Played it for about 1.5 hours using CD player direct to input--no preamp. Heat appears to coming from the center of the sink. The other three are cool. Any thoughts?
 
Make sure you don't have a stray speaker wire shorting. Other than that, it sounds like the bias is off and needs repair. At idle, the heat sink should be roughly body temp - check that.

Murray
 
Pull the driver board for the channel and check the 22 ohm bias resistors, replace them if they read above 22 ohms, they commonly drift to 24 or higher with age. There may also be an 18 ohm one on the board, check it also. One way to prove or disprove the driver board is to swap them and see if the heat follows the board or stays with the heatsink. If the resistors are good and swapping the boards has no effect you most likely have a bad or out of spec output transistor 132-070 = MJ15003.
 
Tested the amp output with a DMM--amp was putting out .27VDC on the left channel, 0.0VDC on the right. Swapped the boards and the voltage offset moved to the right channel. For the 22ohm resistors, do you mean R15 and R39? R-17--18 ohm is also present on the board--according to schematic. Will check. Thanks
 
Terry,

One thing about the driver boards: both L and R are turning black under the large 3.6K resistors--R1 and R2. Is this normal ageing/heating? Thanks. Dave M.
 
Yes check the 18 ohm also, and yes the 3.6K resistor runs hot and will eventually darken the board around it.
An offset reading on an autoformer amplifier doesn't have much meaning since the winding is grounded at one end.
 
Terry,

I don't have a very good DMM but the values on all three seem to be off (readings were taken with one end of each resistor desoldered and lifted from the board):

R-15 (22 ohm) shows 25 ohms.
R-39 (22 ohm--blue ceramic) shows 24 ohms
R-17 (18 ohm) shows 21 ohms

What do you recommend in the way of replacements? If these are so far off value, should I check the others on the board?
 
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