What on earth is this? MC2105

[jefferylhenr]

I acquired a 2105 a couple days ago and now going through it. It’s in very good condition having been to a number of MAC clinics along with obvious maintenance. It plays well and sounds great.

However, looking at the driver boards the large ceramic resistors have an odd white conglomeration on them. What is it? Is it bad and should they be replaced?

 

[avionic]

. What is it? Is it bad and should they be replaced?

Use your imagination.. Do the resistors still measure within tolerance ? Looks like silicone glue to me. Or just a sloppy ceramic sealant ..

 

[jefferylhenr]

Use your imagination.. Do the resistors still measure within tolerance ? Looks like silicone glue to me. Or just a sloppy ceramic sealant ..

@avionic good to hear from you. If I pull them to test, I will just replace them. Why would anyone put goo on these emitter resistors? Looks like a coral reef growing on a couple of them. Never seen this before so had to ask. I have only had them for a day and opened it to do a quick visual. The conglomerate on these resistors is the only thing that looks the slightest bit out of sorts. Otherwise near mint and mostly original. The main filter caps have been replaced and the left channel has new onsemi outputs so someone has obviously been inside. Quickly becoming a new favorite. I have been completely through the c26 and other than a couple new films, a bulb and a couple electrolytic’s, it’s perfect. The last MAC clinic sticker is dated 2015 on both.

 

[Refugee]

You can get these resistors from McIntosh. If you measure them be careful - they have a very low value that is hard to read accurately. Also from what I have read, the amp is apt to go into oscillation if you use low impedance non wire wound types. If the amp is running at a good temperature they are probably good.
2105 and c26 is a great combo...Enjoy!

 

[SiliconTi]

It looks like a sloppy manufacturing job to me, I'd not worry about it myself.

 

[perryinva]

You can measure the values very accurately with an ESR meter. They will have an “L” on the model number if they are inductive. I’ve never seen “growth” like that on any ceramic resistor either, so I would question it too.

 

[Hyperion]

The use of the word growth suggests what you can see wasn't there at some point, and I don't think that has been clarified. From experience the ceramic casing and filler of those resistors is inert. So what you can see is unlikely to be anything to worry about and in my opinion is likely to have been that way as installed.