Hi Chris
I have to agree with you (post #94). I know the design engineer of the 250 family extremely well and later we worked together. We were from different audio companies @ the time. I have had the same things said about my products. I don’t let the armchair reviewers get to me as I don’t respond to them. The tech or other service fixers are not educated engineers and fix / patch products with newer faster or substandard parts and then say bad things about the products.
The 70’s were still early development in semiconductors technology and we had challenges that today are not needed as they don’t have the same constraints. Today we have new obstacles are still showing up for new product designs.
Duke
I have to agree with you (post #94). I know the design engineer of the 250 family extremely well and later we worked together. We were from different audio companies @ the time. I have had the same things said about my products. I don’t let the armchair reviewers get to me as I don’t respond to them. The tech or other service fixers are not educated engineers and fix / patch products with newer faster or substandard parts and then say bad things about the products.
The 70’s were still early development in semiconductors technology and we had challenges that today are not needed as they don’t have the same constraints. Today we have new obstacles are still showing up for new product designs.
Duke
I agree that too many threads on AK end without one being able to discern what the end fix was, but I've read this entire thread (one of my first here, and referred by an AK thread) and have had a hard time learning from most of it. Great to see so many posts by those who are without a doubt more knowledgeable, but so condescending, man it makes me so apprehensive to want to ask ANY question here.
Broken Marantz 250 needs MTF cap parts list and
Hi
I'm getting older and unmotivated to start a new project. I boxed up all my electronic equipment into the attic from my amp repair business and have not missed it at all.
However, my Broken Marantz 250 needs TLC. Wondering if there is a (most likely to fail first) cap list and where to buy the matched power transistor list. Do you know what rail voltages I should look at etc. Let me know if you have a list of parts, where to source parts or even a repair place.
Anyone want to fix it for me?
These amps were built in California and I am in the mountains of Northern California.
Mr. Tee
Hi
I'm getting older and unmotivated to start a new project. I boxed up all my electronic equipment into the attic from my amp repair business and have not missed it at all.
However, my Broken Marantz 250 needs TLC. Wondering if there is a (most likely to fail first) cap list and where to buy the matched power transistor list. Do you know what rail voltages I should look at etc. Let me know if you have a list of parts, where to source parts or even a repair place.
Anyone want to fix it for me?
These amps were built in California and I am in the mountains of Northern California.
Mr. Tee
Gents,
this is the most important thread for Marantz 250B repair in this valued forum.
For a good schematic please see
https://www.diyaudio.com/community/threads/marantz-250m-bias-throws-dc-offset-off.347032/
Additional info is here :
https://www.diyaudio.com/community/threads/marantz-250m-clipping-artifacts.384561/#post-6979638
I agree with Anatech Chris that this is a straightforward design and I can see no
serious issues and no tendency for undue oscillation.
If you receive an amp for repair that is still in original condition it is almost sure
you can overhaul it with adequate effort.
I also agree that you should not do random changes to components. Chris hinted
at the professional tantalum caps, but these do not appear in all models, see this
picture :
https://www.diyaudio.com/community/threads/marantz-250m-repair.148403/post-2534300
I would agree to throw away the blue Philips caps seen here.
However, an exchange of the caps parallel to the 18 volts Zener diodes will not hurt
even if you replaced the mil spec tantalums.
More important in my view is a check of the feedback cap, 220 μF, it is C 507 in the schematic.
Curiously enough I found that the voltage amp transistor Q 503, MPSA 65 is prone to
failure although it operates from a 2 x 18 V supply only. I found this one defective today
and see that it was exchanged in the other channel also in the past.
this is the most important thread for Marantz 250B repair in this valued forum.
For a good schematic please see
https://www.diyaudio.com/community/threads/marantz-250m-bias-throws-dc-offset-off.347032/
Additional info is here :
https://www.diyaudio.com/community/threads/marantz-250m-clipping-artifacts.384561/#post-6979638
I agree with Anatech Chris that this is a straightforward design and I can see no
serious issues and no tendency for undue oscillation.
If you receive an amp for repair that is still in original condition it is almost sure
you can overhaul it with adequate effort.
I also agree that you should not do random changes to components. Chris hinted
at the professional tantalum caps, but these do not appear in all models, see this
picture :
https://www.diyaudio.com/community/threads/marantz-250m-repair.148403/post-2534300
I would agree to throw away the blue Philips caps seen here.
However, an exchange of the caps parallel to the 18 volts Zener diodes will not hurt
even if you replaced the mil spec tantalums.
More important in my view is a check of the feedback cap, 220 μF, it is C 507 in the schematic.
Curiously enough I found that the voltage amp transistor Q 503, MPSA 65 is prone to
failure although it operates from a 2 x 18 V supply only. I found this one defective today
and see that it was exchanged in the other channel also in the past.
The capacitors are wet slug tantalum types. You will not find smaller capacitors, or even the same size that perform as well. If they are good, leave them!
I haven't seen MPSA65 issues before, but that doesn't mean one can't fail, or a bad production run wasn't made. If they are reverse biased, well all bets are off.
Duke,
Fully agree with you!
Mr Tee,
Too bad we aren't closer. I would have. These are nice amps for the time for sure.
I haven't seen MPSA65 issues before, but that doesn't mean one can't fail, or a bad production run wasn't made. If they are reverse biased, well all bets are off.
Duke,
Fully agree with you!
Mr Tee,
Too bad we aren't closer. I would have. These are nice amps for the time for sure.
Hi Anatech. Many thanks. I may replace a few components if necessary, but as per the original design. I will use the suggested replacement BJTs, but again only if necessary. Someone has already been inside the box, and if I recall correctly, replaced two of the main output transistors but in the process butchered the cabling and semi-melted a cap. I specifically want to keep it as original as possible. AAMOI, I also have a Bedini 25.25 to rebuild sometime. And again keep it as original as possible. I will have to have new PCBs made though. There are tracks lifting off on the original PCBs. The PSU PCB is still fine, though the transformer is shot. I'll have a new one made-up.
Regards.
Regards.
Hi ferret,
Well, the outputs should be the same make and number family. I would use MJ2119x parts today for the outputs. You may have to adjust the feedback compensation.
Which amp has the damaged PCBs and dead power transformer? Is the transformer burned, or just an open thermal fuse?
My own personal opinion. The Bedini is worth more selling on than repairing. My experience is that the performance never matched the hype. Construction quality is also rough.
Well, the outputs should be the same make and number family. I would use MJ2119x parts today for the outputs. You may have to adjust the feedback compensation.
Which amp has the damaged PCBs and dead power transformer? Is the transformer burned, or just an open thermal fuse?
My own personal opinion. The Bedini is worth more selling on than repairing. My experience is that the performance never matched the hype. Construction quality is also rough.
Hi Anatech. Indeed the MJ2119x BJTs is what I intend to use. The transformer for the Bedini is the one that is toast. As far as the construction is concerned, I agree that the construction was not great, but then a known dealer here in South Africa got hold of it and made a few mods to it, so he may have been the responsible person for mucking it up. Pictures that I have seen of other Bedini 25.25s showed a pretty good build quality. While the Bedini was working, it was the perfect amp for my stacked Quad ESLs. I have had a few other amps to drive the Quads (Quad 405, Krell KSA50, ISIS tube amp, Hafler DH-200,) but nothing got close to the Bedini-Quad clarity, and mid-range sweetness. Not a perfect bass, but good enough for my ears - though recently I have added a sub-bass which has enough adjustment to get a good, but not overpowering, bass response. The rebuild is a nostalgic tribute to an amp that gave me incredible value for money for nigh on 30 years. I only needed to repair it once when a close by lightning strike fried the BJTs on the one channel - the 2N3055s were replaced with MJ802s on both channels, and the MPSAs with BC550/560s. Fortunately, the 2N3440 and 2N5416s are still available, though there are alternatives if neccesary. The problem with the tranformer was that after 30 years off use the continupus high temperature caused the insulation on the primary and secondary windings to start cracking up, and the fibre "potting" to start disintegrating.
Regards, Kevin
Regards, Kevin
Hi Kevin,
Okay, excellent on the 250.
Bedini amplifiers I have serviced all had rough build quality compared to something like the 250. This was factory build. The dealer may have messed it up, you're right.
You've had it for a while and it works for you - so good enough. If you can reduce the temperatures in the chassis and transformer ... You should seriously consider lowering the bias current as it probably doesn't need to be as high as it is. That was a fad, and still is. I would refuse to buy a Krell for that very reason.
Okay, excellent on the 250.
Bedini amplifiers I have serviced all had rough build quality compared to something like the 250. This was factory build. The dealer may have messed it up, you're right.
You've had it for a while and it works for you - so good enough. If you can reduce the temperatures in the chassis and transformer ... You should seriously consider lowering the bias current as it probably doesn't need to be as high as it is. That was a fad, and still is. I would refuse to buy a Krell for that very reason.
Hi Anatech,
I have in fact got better, albeit slightly longer and deeper heatsinks from Conrad in Australia, for the Bedini. It will look exactly same from the front, just deeper and the heatsinks will stick out a bit more on each side. And of course new components throughout - which I already have.
Kevin
I have in fact got better, albeit slightly longer and deeper heatsinks from Conrad in Australia, for the Bedini. It will look exactly same from the front, just deeper and the heatsinks will stick out a bit more on each side. And of course new components throughout - which I already have.
Kevin