Pictures from the bench

c_dk · Oct 18, 2014

Had these two Mac amps come in a few weeks ago.....with an important problem as well as a huge challenge.

This Mc2100 upon bench testing could deliver maybe 3 watts before distortion pegged the Sound Technology meter. Pulled the bottom cover and cage and found three heatsinks flopping around, 6 of the 8 phenolic mounting bracket/stand offs were shattered. This amp came out of the big city, could have been used in a bar, but I think it was a roadie.

There are no burn marks on the driver cards. pulled the outputs and they are not shorted but the positive feed wires have gotten very hot. I think the heat sink at +35 volt shorted to the cage.....important for all you first gen transistor owners to keep track of.

Second set of pics is of a MC2125 meter set. I have never in 36 years seen a set so busted up. Has any one else? Fortunately the new owner works for the local company that supplies LED lighting to the police/emergency vehicle market....he is searching for a solution.

c_dk · Oct 18, 2014

Oh, the shop might make a profit this month, previous perpetrator needed shims, the one looks to be just a washer but the other appears to be 6 cents!

62caddy · Oct 18, 2014

Lol - don't spend it all in one place.

My 2125s have holes drilled in tops of the meter housings - I guess that is why they held up better...

ConradH · Oct 18, 2014

Wow, pretty rough! BTW, what's a "profit"?

damacman · Oct 18, 2014

Wow . . . those meter assemblies are trashed.

clinic-audio · Oct 18, 2014

Hello Chris !

I have never in 36 years seen a set so busted up. Has any one else ?

YES , I did ! I got worse !

see my picture :tears::nono:

clinic-audio · Oct 18, 2014

The same renewed !

:yes: :banana:

clinic-audio · Oct 18, 2014

Another drasticly damaged !!

jlovda · Oct 18, 2014

clinic-audio said:
The same renewed !

:yes:

I'm surprised the two clips survived. Long term heat on the plastic will cause them to break by just looking at them.

clinic-audio · Oct 18, 2014

Hello John !

You are perfectly right but I am using brand you part !

In my example I use for MC2125 meter , housing of MC2155 meter they are 100% identical except the 3 holes above to cool the temperature inside the MC2155 meters

:thmbsp:

you have the result on the pair in the last picture

c_dk · Oct 18, 2014

Did you gut a mc2155 meter to get the case or do you have a secret source for these cases?

damacman · Oct 18, 2014

Knowing Patrice, he's likely got some local company pressing those out!

c_dk · Oct 18, 2014

In that case, I'll take 3 pair.....we do not have any trade issues with France, do we? I did ask Mac if they had any mc2155 meters and they said no, or did I ask if they had just the case.....don't remember. I was trying to explain to the parts guy that the cases were the same.......

clinic-audio · Oct 18, 2014

I did ask Mac if they had any mc2155 meters and they said no,

Yes and since many years ...

or did I ask if they had just the case.....don't remember.

They don't have it

I was trying to explain to the parts guy that the cases were the same.......

I don't think that Brian knows that ...Anyway these are no more available ....

I did contact thec manufacturer itself sometime ago (around one year , I don't remember ) and the price was very expensive and I did not have enough request for meters to place an order to him so I decided to no spend my money in this project for now .
May be in the future if needs grow !

:thmbsp:

c_dk · Oct 18, 2014

My shop back door neighbor has a company that sells 3D printer kits, has a few comercial printers himself that he uses to make parts for the kits. Think I will have to have him take a look......

clinic-audio · Oct 19, 2014

Hello Chris !

Good idea ! 3D printer may be the solution ....

I am working on another one ....

62caddy · Oct 19, 2014

Chris or Patrice,

Slightly OT but if you know a way to keep that meter lamps from flickering to the music at high output, please post it.

c_dk · Oct 19, 2014

They are fed by AC right off the transformer......dedicated 10 or 12 gauge AC directly to the amp would usually solve this issue (and room light dimming) after I would bring my variac on a house call, most often to find out why customers kept blowing speaker fuses or drivers.

clinic-audio · Oct 19, 2014

62caddy said:
Chris or Patrice,

Slightly OT but if you know a way to keep that meter lamps from flickering to the music at high output, please post it.

I saw that sometime ...I think you are listen at very high level ..Don't you ?
I think the the trouble is coming from the transformer itself . Can you confirm that all the 6 lamps are lightning following the bass from the audio signal ?
The winding for lamp power supply is not right placed when the transformer was manufactured ...
In my point of view the best way to cancel this is to build a power transformer in another way that it was produced in 1976 ...38 years ago ...:scratch2:

c_dk · Oct 19, 2014

Patrice

Do you have a MC2155 meter case to take a laser scan of?

These cases are beyond hope, I could pull apart a MC2125 I have around but if you have one........

Pictures from the bench

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