Marantz 250M rebuild by Bob Speece

[airtime]

I wanted to post this for a while now. Bob did an amazing job on this jewel of an amp. And BTW it sounds every bit as good as my coveted Latino ST-70 tube amp.

If I miss a step I hope Bob jumps in and adds to it.

First old caps out and heat sinks removed


All the old heatsink compound and mica insulators removed and heatsinks cleaned up...


Newmain filter caps on the left with the old original caps on the right


Over the last several days I have finished the relay protection board and the left amp board.
Before....


After


This is a list of some of the things Bob did as well.

I replaced the drivers with new correctly matched 2SC783 and 2SA483's with new mica insulators and Dow 340 heatsink compound making sure that the small nylon spacers were in place.

I replaced the predrivers with new matched ST 2N3440 and 2N5416's.

I replaced the differential input pair with matched and heatshrink bonded MPS6519's.

Used Vishay AML138 for the axial caps and a Panasonic FC for the 100uf tantalum C527.


Tomorrow I plan on working on the right channel amp board with the same treatment.

Those oem original type Toshiba TO66 and ST 3440/5416 transistors are rare and hard to source but they are the best and look far better than shoehorning in some TO220's like others do.

pics of the flyback diodes mod that is detailed in Service Bulletin M-250-3.


I have the new OnSemi MJE21195/96 output transistors installed on their heatsinks with new mica insulators and Dow 340 heatsink compound.


Both new 24,000uf 100v main filter caps are in ,along with their Panasonic 2.2uf poly film bypass caps....


New LED lamps using Don Haywood's premium lamps.....

 

[mcheinstein]

Looks beautiful, Airtime. Thanks again for helping me out in my thread on the 1200. I'll be following this one!

 

[KutzlerTrans]

Mr Bob is one of the Best
Congrats on the unit. Now you can blow the doors off of the place.

 

[Steven Tate]

Fantastic looking unit! I'm sure Bob has that thing ready to crank it up for many years to come.

 

[airtime]

I didn't want to get into an audio review as much as point out the detail that Bob did restoring this beauty.

However sonically speaking it's awesome sounding. Honestly I wasn't expecting it to sound as good as it does. Now I look forward to using it in the rotation even against my tube amps.

 

[SWL3600]

Awesome. I'm looking forward to Bob restoring my 250 this fall. Can't wait!

 

[audiobeer]

I wish I had room to list all the items Bob has restored for me. He’s rebuilding my Marantz 4400 and has a 250M and 33 Preamp he’s getting together for me. He’s “The Man” when it comes to Vintage equipment!

 

[Steven Tate]

I wish I had room to list all the items Bob has restored for me. He’s rebuilding my Marantz 4400 and has a 250M and 33 Preamp he’s getting together for me. He’s “The Man” when it comes to Vintage equipment!

Agree 100%

 

[txturbo]

Really nice! I am a sucker for the blue PCB's.

 

[airtime]

I'm listening to it RIGHT NOW. It's STILL a wow feeling when I turn it on

 

[airtime]

For years I've been trying to like my NAD C275BEE power amp. But every time I plug it in and go back to the 250M I relearn what a jewel the 250M is. So once again the NAD will sit in the closet for another few years

This NAD amp is about 8 years old and has less than 200 hours on it. Why use it when I the 250, VTA ST-70 and Sherwood.

 

[SWL3600]

I'm listening to it RIGHT NOW. It's STILL a wow feeling when I turn it on

Yer killin me....

 

[SWL3600]

Until my 250 goes to Bob for repair/restoration.....I've been using my restored 3300/1200b combo. I know the preamp in the 1200b is essentially a 3300 but after comparing both scenarios, for some reason using the separate 3300 pre sounds better.

I'm anxious/curious to hear the difference in performance....if any....when I get the 250 back and compare it to the 1200b. In the meantime I absolutely dig the 1200b.

 

[airtime]

The 3300 is a wonderful match for the 250.

You're gonna be VERY happy with that 250 rebuild

 

[audiobeer]

I wish I had room to list all the items Bob has restored for me. He’s rebuilding my Marantz 4400 and has a 250M and 33 Preamp he’s getting together for me. He’s “The Man” when it comes to Vintage equipment!

Well I got it back and works like a new one would. Anyone that says it is a sacrilege to make it black must know it’s easy to make it go back! Thanks again Bob Speece, I couldn’t be happier unless of course you delivered it with Beer and Pizza!

 

[JediDude]

Well I got it back and works like a new one would. Anyone that says it is a sacrilege to make it black must know it’s easy to make it go back! Thanks again Bob Speece, I couldn’t be happier unless of course you delivered it with Beer and Pizza!

Looks good.... ;-})>

 

[Bkphoto]

I wish I had room to list all the items Bob has restored for me. He’s rebuilding my Marantz 4400 and has a 250M and 33 Preamp he’s getting together for me. He’s “The Man” when it comes to Vintage equipment!

He did mine also...!

 

[Pete B]

Those new PSU caps look like, but I have to check the dimensions to be sure:
Cornell-Dubilier DCM243U100DC2B

I have one of these that needs a recap.

 

[airtime]

Contact Bob for the exact part number.

As I've already posted it sounds AMAZING

 

[wlhd1610]

Thanks for all the kind words guys.

This is the cap I use:
DigiKey 565-3679-ND

24,000uf 100V screw terminal fits perfectly in existing brackets.


Bob