Marantz 8B Replica Build

[sgerus]

Don't do it! The Marantz 8B, McIntosh 2nn models, and the H/K Cit. 2 are revered, in no small part, due to the high current, low impedance, SS rectified, B+ PSUs employed. The superior bass performance delivered is directly related to SS rectified B+.

Thank You ELI

I completely agree with you as to the bass performance. I thought that all the amp manufactures switched to SS rectifier as a cost saving measure.

I also thought they used voltage doubles as a cost saving measure as well.

Now I get that it's the SS rectification AND the voltage doubler (ie the power transformer has a lower secondary resistance compared to one using a full wave rectifier) both contribute to the low impendence!

 

[Eli Duttman]

The profit motive is always present. When those "killer" amps were designed, it was not possible to buy, at anything resembling reasonable cost, the high PIV SS diodes we take for granted, now. The "full wave" doubler worked with the best available diodes and also happens to exhibit low copper losses. The McIntosh 275 does not use a doubler, but I believe it was the last of those great amps introduced.

 

[77seriesIII]

Sergus, Your build is by far spectacular! Whom ever said earlier that you have 'the touch' is spot on, excellent crafts- and workmanship. Plus if SY gave you kudos on finished product, that in and of it self speaks volumes. Well Done!

./e

 

[sgerus]

Sergus, Your build is by far spectacular!

Thank You 77 SeriesIII

This post is to show how I start the design process.

I'm starting to design my next 8B replica, which will use a different power transformer(s) in order to do a voltage doubler.
So the pic's posted here are of the "next amp".

Here are some tips:
1. Draw to full scale.
2. Add as much detail as you can.... i.e. mounting screw locations, switch's, fuses etc. (the picture is still a work in progress)
3. Have as many of the parts on hand as you can, mainly the transformers, power supply caps and coupling caps.
4. Make copies of the final layout. If you have a way to invert the drawing use that to layout the components in the inside of the amp, starting with the heater wires then the power supply.

For those of you old enough to have taken a "drafting" class, check out my makeshift drafting board, circle template and erasing shield. I regret to say to got rid of my T-Square years ago.

Yes, that's a wise beer in the 2nd picture.... It was a perfect pour but I didn't get the camera out in time to catch it!
On a serous note, never drink mess around with 470VDC
470VDC can KILL you!

 

[Bigun]

Just when I didn’t think I could be any more inspired by this wonderful thread I spotted the Erdinger !

 

[sgerus]

WOW... I'm surprised it took over 3 years for someone to comment on the beer!

These days I'm building 300B SE apps. If your interested check out 300amps.com

 

[ziffel]

I love your work. It's inspiring.

Would you give us some details on your brake, bending and any other tools that might be informative for us wanting to build a chassis at home?

Also, how did you like the Marantz replica vs a 300B?

Thank you and best wishes - AZ

 

[The Lord Flashheart]

Fantastic project, I really like the marrying of mechanical and electronic skills to make a complete product.

 

[vinylkid58]

For those of you old enough to have taken a "drafting" class, check out my makeshift drafting board, circle template and erasing shield. I regret to say to got rid of my T-Square years ago.

Haven't done any real drafting on paper since the 80's. All done on computer since.

Stunning looking amp BTW.

jeff

 

[El Sid]

WOW... I'm surprised it took over 3 years for someone to comment on the beer!

These days I'm building 300B SE apps. If your interested check out 300amps.com

Should be 300bamps.com.

Beautiful amps!

 

[El Sid]

Haven't done any real drafting on paper since the 80's. All done on computer since.

Stunning looking amp BTW.

jeff

I still draw my circuits with pencil and paper. Is that wrong?

 

[meanie]

Impressive replica !
Subscribed.

 

[Bigun]

I'd like details about the brake too. I'm not sure I have the skills but I have had a goal for awhile now to make a replica of a Shindo power amp and a Shindo preamp. As far as I can see, Shindo took a lot of inspiration from Marantz and then painted the box green instead of bronze so your project in this thread is a great inspiration for me.

 

[sgerus]

Should be 300bamps.com.

Beautiful amps!

EL Sid, Thanks for catching my type o. Your correct, My website is 300bamps.com


Here are some pictures of my DIY bending brake and some other tools.
As to what other tools you need to build a steel chassis:
1. Jig saw / mild steel cutting blades
2. Files and sand paper
3. Drill / bits / Drill Press
4. Greenlee Knockout set (can always find them on ebay)
5. Good work bench, clamps, propane torch
These days I build wood/steel chassis that don’t require any soldering!

As to the sound of the amplifier:
It was very different than the DHT / SE amps I had in the past.
The sound was unique and mellow. I suspect that the vintage capacitors and AB resistors attributed a lot to the sound.
My other experience with PP amps was a KT88 PP with Plitron Iron, Very $$$$$$
The specs on that amp where the best of anything I have made. It was so perfect that it sounded like a SS amplifier!
Lesson learned, amps that measure the best don’t always sound the best.
Just so you know where my opinion comes from
1. 3.5 watts is all the power I need
2. I prefer DHT (directly heated triodes)
3. I prefer SE (Single ended)
4. I believe in “less is better”

 

[ziffel]

I'm very impressed that you do such beautiful work with these simple tools. It gives me hope.
Thank you for these pictures. Now it's time to get a brake and experiment.

I too prefer SE amps. I'm very fond of the 845. Like you, I have found that many amps that measure well in the lab don't sound so good in the home. It makes me think they are still measuring the wrong things.

Thank you again. Ciao!