C26 and C28 recap questions/can sizes

Hi,

I've got both a C26 and C28 preamp sitting in my workshop that were brought in to be recapped. I've noticed looking at the schematic (and pictures) that these units have a couple of multi-section cans.

I'm not sure if I'm going to replace these entirely, or gut the cans and restuff them. But what I'd like to know without having to crack it open are the physical sizes of the cans.

If anyone has this info handy. I'd greatly appreciate it.

Also. I'm looking at the C26 service manual and notice a large presence of film/mylar caps (I haven't looked at the C28 yet), I know from a technical standpoint...these are probably still fine. However, if anyone has some suggestions of brands to put in there (or to leave them be); that would also be great.



-Jay

I took on a C28 project, to do some experimentation, a year or so ago. Biggest improvement came from creating a better ground layout and replacing interconnection wiring with shielded cabling.

Well, I might do that; except I don't know if the C28 is worth all that. The front faceplate is missing a piece, and I'm not sure if the owner wants to spend the money on a new one. I know that's gotta drop the value.

I'm new to Mac gear. I previously recapped a MC7270 that came out fantastic; I don't own any...I just "refurb" it.

dewdude said:

Well, I might do that; except I don't know if the C28 is worth all that. The front faceplate is missing a piece, and I'm not sure if the owner wants to spend the money on a new one. I know that's gotta drop the value.

I'm new to Mac gear. I previously recapped a MC7270 that came out fantastic; I don't own any...I just "refurb" it.

Click to expand...

I attempted to recap a C28 because of the number of tantalum caps. Several of the caps are unreachable. The solder connections on the bottom of the circuit boards are completely covered by shielded wires. I wasn't about to unsolder those.

What is measured the S/N of the phono and line level? Terry posted a spectral plot years ago showing the noise centered around 60 and 120 hertz. A new star grounding plan and shielding the twisted interconnecting wires can improve the S/N by 10 dB. This is a big deal on units I update for locals and sets the foundation for cap updates.

dewdude said:

Hi, I've got both a C26 and C28 preamp sitting in my workshop that were brought in to be recapped. I've noticed looking at the schematic (and pictures) that these units have a couple of multi-section cans.

I'm not sure if I'm going to replace these entirely, or gut the cans and restuff them. But what I'd like to know without having to crack it open are the physical sizes of the cans. If anyone has this info handy. I'd greatly appreciate it.

Click to expand...

I've dug into the C26 in great detail and replaced the tantalum and electrolytic caps. The multi-section caps are still original. The C26 produces some hiss when driving the MC2205 in the Blu-ray video setup. You can find posts about the project by searching: https://www.google.com/search?q=C26+Gregory+site:audiokarma.org

The the MC2505 multi-section caps were gutted, but I opted to install custom m-s caps from a vendor in the midwest. Search https://www.google.com/search?q=2505+caps+Gregory+site:audiokarma.org

These were both enjoyable projects.


-Gregory

c_dk said:

What is measured the S/N of the phono and line level? Terry posted a spectral plot years ago showing the noise centered around 60 and 120 hertz. A new star grounding plan and shielding the twisted interconnecting wires can improve the S/N by 10 dB. This is a big deal on units I update for locals and sets the foundation for cap updates.

Click to expand...

I think he was asking about caps. Have you posted a clear description of your shielding and ground plan? It's not too well understood.


-Gregory

dewdude said:

I've got both a C26 and C28 preamp sitting in my workshop that were brought in to be recapped. I've noticed looking at the schematic (and pictures) that these units have a couple of multi-section cans. I'm not sure if I'm going to replace these entirely, or gut the cans and restuff them. But what I'd like to know without having to crack it open are the physical sizes of the cans. If anyone has this info handy. I'd greatly appreciate it.

Also. I'm looking at the C26 service manual and notice a large presence of film/mylar caps (I haven't looked at the C28 yet), I know from a technical standpoint...these are probably still fine. However, if anyone has some suggestions of brands to put in there (or to leave them be); that would also be great.

Click to expand...

Why is there a hesitancy to opening the covers? Or do you mean crack the cap-cans open? :scratch2:


It would be best IMHO to measure your caps and make a sketch in your notebook. See example below:



After all the measurements to 0.001" and adding/subtracting, it's easy to see BOTH THESE caps are 3" high, 1-3/8" dia. :yes:


Mind you, we're using the 2505 as an example. Here are my original 2505 cans ready for stuffing.




And a view from the web {origin unknown} of a re-stuff job.




This kind of activity can be very enjoyable... and for years to come listening. :thmbsp:


-Gregory

Gregory,
I always enjoyed your posts, specially your restoration ones with all the details, pictures and drawings. Very meticulous and detail oriented; as an engineer I really appreciate that.
Thanks for your effort. :thmbsp:

Ditto that. Very appreciated from another engineer.

I didn't mean to abandon this thread; I was pressed on time to make an order for a couple of things...and I don't like making small mouser orders. Everything I bought fit.

Why is there a hesitancy to opening the covers? Or do you mean crack the cap-cans open?

Click to expand...

In the case of the MC2105, it's simply I can't move that heavy thing a whole lot. I just dislike disassembling stuff, taking measurements; then reassembling enough to put it in storage. At my old job I was forced to have half finished projects lying around while I waited for the boss to order stuff; and it just irk's me. Plus I feel like I gotta handle this Mac gear with kid gloves. I see what the prices of some of these things are going for on eBay...and I have no intention of purchasing one "by accident".

c_dk said:

I took on a C28 project, to do some experimentation, a year or so ago. Biggest improvement came from creating a better ground layout and replacing interconnection wiring with shielded cabling.

Click to expand...

I just started a c28 restoration project. Can you give me a bit more detail on what you did grounding wise to improve it. I am fighting some bad hum on one channel as well as a missing section of carbon trace on one half of the volume pot. Once I get that addressed it will be getting a full recap. I don't think this noise is related to either so bad ground would be a likely suspect.

Thanks