MC2505 catastrophe

[SaturationPt]

It looks like the MAC factory changed the values of at least one of the two FP cans during later years. The later MC2505-2 don't have as many multi-sections as your picture shows.

Try and track down the correct service manual for your early version based on your serial number. Since yours is from 1968, you might have a "version 1". I think there might be as many as 5 service manuals for the 2505.

See below. Look at the FP can in the lower right with the phenolic wafer. On yours, based on the wiring, this can appears to have multiple sections. Whereas the later MC2505-2 versions have a single 500uf section connected while the rest of the wiring goes to the can common.

It looks like you might need as many as 7 discrete capacitors to replace the two FP cans under chassis. This is why you need to hunt down the correct service manual for your serial number. Maybe someone here has a pdf they can send you...

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It appears that the 2505-1 and the 2505-2 both are using two values in the right (isolated can) multi-cap since the can/common is not connected in the 2505 only in the 2505-2.

This is a perfect time also to apply the updates to the 2505-1 that improve the available power to match that of the 2505-2.

See pages 24+ in the attachment on the 2505-1

 

[Benz]

I van't see any signs of tampering or modification on the multi can, it appears untouched.

Now this is where the plot thickens... based on year of purchase and helpful info provided by Monk and Jeff, this should be an early model, 2505-1. However, when I look at the chassis, my amp appears to be a later 2505-2 (see pics). The service manual I have is from Hifi Engine, and states that it is for serials starting with 36K00. Now I'm properly confused.

 

[monkboughtlunch]

Now this is where the plot thickens... based on year of purchase and helpful info provided by Monk and Jeff, this should be an early model, 2505-1. However, when I look at the chassis, my amp appears to be a later 2505-2 (see pics). The service manual I have is from Hifi Engine, and states that it is for serials starting with 36K00. Now I'm properly confused.

View attachment 2872864 View attachment 2872865 View attachment 2872866

You have a very early MC2505-2. And your 33K94 serial checks out OK. In fact, your unit appears to be within the first 200 or so 2505-2 units produced.

See:

http://www.mcintoshcompendium.com/Compendium Docs/Power Amplifiers/PDFs/MC2505.pdf

From the @VintageMac compendium:

“MC 2505 meters featured bezels that were recessed behind the glass and had a Meter Range switch from OFF to 0.

Somewhere between the 32Kxx serial number and the 43Kxx serial number, the model designation was changed to MC 2505-2 and featured meters without the bezels and mounted against the glass. The METER RANGE switch for the MC 2505-2 was opposite that of the MC 2505 and ranged from -20 to OFF.”

Can you post a picture of your front faceplate? Does it have bezels around the meters? Based on the compendium, your unit should not have bezels. The interesting thing is your unit serial indicates that the factory switch to MC2505-2 occurred in 1968.

This appears to indicate the rare 2505-1 units with meter bezels were only produced in 1967 and 1968.

 

[monkboughtlunch]

I can’t see any signs of tampering or modification on the multi can, it appears untouched.

And you have visually confirmed that the 1996 repair shop did not restuff any of your four silver filter cans in the power supply.

This means your power supply caps are all at least 55 years old and past their design life span. This doesn’t mean they are necessarily bad, but they should be considered as a possible cause of your issue. It would be prudent to replace them regardless —if long term reliability is important.

Additionally, you have verified the 1996 repair shop billed for four capacitors that were not installed.

 

[monkboughtlunch]

@Benz you need this service manual: 26K01 to 35K99. Maybe someone on this forum has it and can share it with you...

 

[Celadon]

@Celadon had his original 2505 big filter caps physically leak. So even though the old GE 9300uf cans last a good long while, they can and do fail: https://audiokarma.org/forums/index...-filter-cap-information.955515/#post-14683748

Yes, indeed i did!
Actually only one physically leaked -- and if I remember properly it still tested good value/ and ESR -- with my Peak tester.
Probably should retest and verify that sentence about value and ESR.... before I commit to that -- (they say the memory is the first thing to go, and I can't remember the rest).

I would have NEVER discovered the physical leakage until I pulled the amp out of service to detail it .... (small dime size) corrosion that was undetectable till I pulled the actual offending cap --


So upon testing one of the multi can caps -- values are WAY OFF!
was going to restuff, but just found a great replacement by CE ....

Still working on life issues, but need to find the procedure for setting DC Balance --- a NEW topic I will ask about soon. W/ pics as soon as life permits
Had asked b4 -- but...

oops probly should read this entire thread ......

My best to all!

Celadon -- the man standing behind the curtain.....

 

[Celadon]

@Benz you need this service manual: 26K01 to 35K99. Maybe someone on this forum has it and can share it with you...

View attachment 2873427

I actually have that original service manual ---

If I can help let me know, and lets see how I can scan a copy or ....

I have like 5 versions of the SM for this amp - but my 2505-2 has long had the serial number gone awol so I still do not know, although it IS a 2505-2

Celadon

 

[monkboughtlunch]

@Benz, celadon has the SM you need…

 

[Celadon]

Read the entire thread --and Benz, very informative -- such an awesome community here --
If any photos of my 2505-2 would help I will take some pics and post ---

As I had said, there is NO way I would have known that one of the big filter caps had physically leaked untill pulling it (2 screws) and physically looking... pissed me right off!! as my chassis was deteriorated ... grrrrr

The 2505 is such a magical amp -- it deserves the best

~C

 

[Celadon]

@Benz, celadon has the SM you need…

Indeed I do !

 

[monkboughtlunch]

AKer @c_dk (RIP) posted this about 2505 hum a few years ago. He also theorized: either a faulty rectifier diode, output transistor or main filter capacitor…

If one of the diodes that make up the bridge is starting to leak it could be using excess current to be drawn, causing the transformer to strain, as would a falling output or shorting out main filter cap.

 

[Celadon]

AKer @c_dk (RIP) posted this about 2505 hum a few years ago. He also theorized: either a faulty rectifier diode, output transistor or main filter capacitor…

Didn't know c_dk ...
But sounds like he was a great asset to the community.

**Regarding the post:
When I first purchased mine, The P/S diodes looked like they had been hot, so I replaced them all.

BTW, Benz -- if you still need a SM, and a Good quality PDF file would help you out ... let me know.. I would have to master the printer, and it isn't too many pages -- probly should go somewhere here on AK as well ...

Ya gotta have a roadmap if you are gonna get where ya wanna go

 

[Benz]

You have a very early MC2505-2. And your 33K94 serial checks out OK. In fact, your unit appears to be within the first 200 or so 2505-2 units produced.

See:

http://www.mcintoshcompendium.com/Compendium Docs/Power Amplifiers/PDFs/MC2505.pdf

From the @VintageMac compendium:

“MC 2505 meters featured bezels that were recessed behind the glass and had a Meter Range switch from OFF to 0.

Somewhere between the 32Kxx serial number and the 43Kxx serial number, the model designation was changed to MC 2505-2 and featured meters without the bezels and mounted against the glass. The METER RANGE switch for the MC 2505-2 was opposite that of the MC 2505 and ranged from -20 to OFF.”

Can you post a picture of your front faceplate? Does it have bezels around the meters? Based on the compendium, your unit should not have bezels. The interesting thing is your unit serial indicates that the factory switch to MC2505-2 occurred in 1968.

This appears to indicate the rare 2505-1 units with meter bezels were only produced in 1967 and 1968.

Very interesting, thanks much for sharing this information and the link to the pdf. My unit doesn't have the bezels, see below:

 

[Benz]

And you have visually confirmed that the 1996 repair shop did not restuff any of your four silver filter cans in the power supply.

This means your power supply caps are all at least 55 years old and past their design life span. This doesn’t mean they are necessarily bad, but they should be considered as a possible cause of your issue. It would be prudent to replace them regardless —if long term reliability is important.

Additionally, you have verified the 1996 repair shop billed for four capacitors that were not installed.

Yes, I think I will do that regardless, as you suggest. I had a MAC1900 recapped last year and I love the peace of mind, the thing might outlast me now. It had a bad transistor and thought I might as well do a proper resto given the age of the receiver.

Re: the 4 "missing" caps; that's just sad if they in fact never did the work and charged the previous owner.

I actually have that original service manual ---

If I can help let me know, and lets see how I can scan a copy or ....

I have like 5 versions of the SM for this amp - but my 2505-2 has long had the serial number gone awol so I still do not know, although it IS a 2505-2

Celadon

Didn't know c_dk ...
But sounds like he was a great asset to the community.

**Regarding the post:
When I first purchased mine, The P/S diodes looked like they had been hot, so I replaced them all.

BTW, Benz -- if you still need a SM, and a Good quality PDF file would help you out ... let me know.. I would have to master the printer, and it isn't too many pages -- probly should go somewhere here on AK as well ...

Ya gotta have a roadmap if you are gonna get where ya wanna go

Much appreciate the offer Celadon, but let me see if I can find it online before you go through the trouble. Thanks to Monk now I know which version to look for.

EDIT: Scratch that... I went back to the pile of documentation that was provided to me when I purchased the amp/pre... and bingo, the correct SM was included!!

 

[Benz]

Read the entire thread --and Benz, very informative -- such an awesome community here --
If any photos of my 2505-2 would help I will take some pics and post ---

As I had said, there is NO way I would have known that one of the big filter caps had physically leaked untill pulling it (2 screws) and physically looking... pissed me right off!! as my chassis was deteriorated ... grrrrr

The 2505 is such a magical amp -- it deserves the best

~C

ok, very good to know, I will actually remove them and look.

I could not agree more about your last comment. There is no way this amp will be left in its current condition; it needs to be brought back to health. Perhaps it's my room/room acoustics but the MC2505 + MX112 + Yamaha NS-1000M sound particularly good to me. I've paired the MC with all sorts of speakers over the years and that's the end game for me, with this amp.

 

[Benz]

Big caps look good, I think, at least as far as any obvious leakage.

 

[monkboughtlunch]

@Benz the plastic discoloration on the bottom of your GE filters doesn’t look quite right to me. It may be from excess heat or possible electrolyte leakage that dried.

Statistically, the four section multi-can is usually the first in the power supply to fail (because it has less electrolyte), but that doesn’t mean the big 9300uf GEs can’t fail or diminish in performance.

Here’s what my GE cans look like. No discoloration at all. Mine tested OK on an ESR meter. But I don’t have a tool to test for leakage at rated voltage. By the way, I’m still using my original GE 9300uf filters, but I should probably change them.

The fact yours are discolored at the base suggests they might be heating up for some reason. Another potential reason is possible plastic chemical reaction to chrome polish.

 

[Benz]

@Benz the plastic discoloration on the bottom of your GE filters doesn’t look quite right to me. It may be from excess heat or possible electrolyte leakage that dried.

Statistically, the four section multi-can is usually the first to fail (because it has less electrolyte), but that doesn’t mean the big 9300uf GEs can’t fail or diminish in performance.

Here’s what my GE cans look like. No discoloration at all. Mine tested OK on an ESR meter. But I don’t have a tool to test for leakage at rated voltage. By the way, I’m still using my original GE 9300uf filters, but I should probably change them.

The fact yours are discolored at the base suggests they might be heating up for some reason.

View attachment 2873795

Wow, yours look like new compared to the ones in my amp. Do I need an ESR meter or are there any tests I can perform with a digital multimeter? I would say that the discoloration looks more like what heat would cause, as I don't see any residue at all, or dried particles.

Btw, I edited one of my above responses but fyi, I did find the correct service manual (from 26K01) in the pile of documents that came with my amp... I hadn't thought to look for a hard copy as I presumed I was using the correct one from HifiEngine. Thanks again for pointing that out to me.

 

[monkboughtlunch]

An ESR meter, like the Atlas Peak ESR70, will tell you the capacitance and equivalent series resistance of a capacitor.

 

[Benz]

An ESR meter, like the Atlas Peak ESR70, will tell you the capacitance and equivalent series resistance of a capacitor.

I went back through the entire thread to extract all of the troubleshooting steps in a separate document, so I can go through them in an organized fashion and take notes as I go. As I was rereading everything I noted you mentioned the use of an ESR meter a few times already... apologies for the redundant questions, and thanks again for the suggestion to use the ESR70. I can get one for $200CAD on AMZ. So far my troubleshooting shopping list includes components for a DBT, a variac and an ESR meter. I will start with the DBT and ESR, as they both appear essential to most TS steps. I already own a couple of DMMs.