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Old 05-13-2009, 10:29 AM
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Gregory Gregory is offline
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Default 2505 servicing

Now I can start a new Topic.

It looks like the original Owner's Manual, and a Service Manual are in the file cabinet with information from Serial No. 15K01 to 18K50. This manual shows DC Balance pots on the Input Section schematic. The only way to verify with certainty is to open up the Mc carton and look the unit over.

Should I just go through the schematic and parts list, and make a list of ALL electrolytic and signal path caps? Any other things to note such as diodes?

The only thing I need is a variable AC base to control the temperature of my '70s vintage Weller WP-25 (25W) soldering iron. This thing can get awfully hot, such that it could burn the old glass-epoxy boards!

-Gregory

Last edited by Gregory; 05-13-2009 at 10:31 AM.
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Old 05-13-2009, 12:14 PM
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First get the serial number and find if it has the extra pots. The early models also had a zener diode pair at each input on the board, they have a tendency to short. The best thing to do is remove them as they were not used in later production. I replace the caps on the input board with Nichicon Muse ES and KZ series. Will match replacement caps to schematic when we get serial number.
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Old 05-13-2009, 01:54 PM
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Quote:
Originally Posted by dewickt View Post
First get the serial number and find if it has the extra pots. The early models also had a zener diode pair at each input on the board, they have a tendency to short. The best thing to do is remove them as they were not used in later production. I replace the caps on the input board with Nichicon Muse ES and KZ series. Will match replacement caps to schematic when we get serial number.
The 2505 is out of the carton but still screwed to the cardboard base pad. Strangely there is no serial number!! The field is blank as if the paint was removed with a chemical. I have a receipt from EZ Teletronics in Chicago (now defunct) for this amplifier, but Hank didn't write a SN on it like he did for the other Mc Amps I bought there. Another label describes the unit as model 2505-2.

Inside the perforated heat sink covers, the power transistors and other hardware & components have a good bit of crud on them. It could use a thorough cleanup and restoration. Three of the four power supply cans (Caps) have a clear plastic wrap on them.. one can has no wrap. Otherwise it has only very minor nicks and paint wear spots.

The question is, what kind of sound could one expect from this amp if it was fully serviced? and how much of a classic is it?

I know you're thinking that someone stole the unit, well that thought did cross my mind, and prior to today I was not aware of the missing SN. It's weird because I've had it for just about 20 years now.

-Gregory

Last edited by Gregory; 05-13-2009 at 07:42 PM.
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Old 05-13-2009, 02:21 PM
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Last version was the MC2505-2, the best of the bunch !! I expect the serial number to be in the range starting at 36K00, you may find it inside on the chassis if you remove the bottom cover. In as is condition it should sound good, with a recap it will open up some and improve on it's imaging and presence.
Serial number was ink stamped on, it is easy to get to over ambitious cleaning and wipe it off with Windex or a slightly abrasive polish.
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Last edited by dewickt; 05-13-2009 at 02:25 PM.
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Old 05-13-2009, 03:54 PM
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Quote:
Originally Posted by dewickt View Post
Last version was the MC2505-2, the best of the bunch !! I expect the serial number to be in the range starting at 36K00, you may find it inside on the chassis if you remove the bottom cover. In as is condition it should sound good, with a recap it will open up some and improve on it's imaging and presence.
Serial number was ink stamped on, it is easy to get to over ambitious cleaning and wipe it off with Windex or a slightly abrasive polish.
I got it turned over and removed the lower cover/half-chassis. It had lots of dust on the inside-bottom of cover. There appears to be quite a bit of tiny metal chips inside the chassis, probably from the cover screw threads. I'm going to blow out the inside with regulated compressed air. Thinking of using windex to hit the cover with, but heard it's too volatile.

None of the PC board part numbers match the schematic, and the circuit layouts are vastly different. Same with power supply!! All of the lamps work and it generally looks real good inside, that is for a '60s assembly job.


Here are the board part numbers:

Input Section: 043795, on schematic: 043-854
Output boards: 043916, on schematic: 043-855


My service manual isn't much use--only in a general way. The first step is to order the appropriate service manual but no serial number was found inside. It may be tricky to get at all of the components, and it's not certain if the power supply cans need, or should be replaced. Still wondering whether to go ahead, send it out, or do nothing.

-Gregory
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