• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Marantz 8 rebuild

C

Codecheck

New Member
This is my 1st post and all of you guys are way above my expertise. I really do not know where to post this, so if it is wrong I am sorry. I rebuilt a Marantz 2275 after viewing wonderful pictures and tutorials on Audiokarma. Previously, I rebuilt a Marantz 8 (not an 8B) with Arizona Cactus capacitors and Russian Paper in Oil capacitors. I used Tantalum capacitors in C3A and C3B because I could not find anything close to the original 15uf/6V electrolytic capacitors. I am not sure that I did the “right” thing so I am reaching out to others to see what they used as a replacement. If you could be please specific and I will try to seek them out? I am just a hobbyist that cannot seem to put a soldering gun down. Thanks!!
David
 
Register to hide this ad
Hi and welcome to AK. Experience I see (and personal experience) with tantalum caps is that they can be prone to failure. The caps in your Marantz 8 are in cathode bypass duty in the first audio stage pentode tube. You need the value to be 15 uF, but the voltage doesn't have to be exactly 6V, as long as it is higher than 6V. Search on Mouser.com or Digikey or other supplier and you'll find 15uF aluminum electrolytic caps with 12 or 16VDC ratings. These will be fine for the application.

Here's a possible example:

https://www.mouser.com/ProductDetail/Vishay-Sprague/TE1129-E3?qs=F0bBuU9YDEyhBz5M6QHKeQ==
 
Thanks Dave451 for your response. I had actually purchased those same Vishay-Sprague capacitors from Mouser and I was originally going to install them but I noticed they had an extreme tolerance of +75% to -10%. Not being an expert, that seemed like a large tolerance. I have read that one should not use N.O.S. electrolytic capacitors but I do not know what other options I have. I could use a radial capacitor instead of a axial capacitor which might give me more options. My ultimate goal is to keep it sounding as close to original without starting any large fires. Thanks again! David
 
My experience with modern caps is, listed tolerances notwithstanding, that they come in pretty close to the listed capacitance value (I measure pretty much all of them). In any case, though, search on radial types and you will find many that are +/- 20%, which is about as good as it gets for aluminum electrolytics. It is traditional for electrolytic caps to be plus higher tolerance and minus low tolerance, since more is not usually a problem, but less can be. There is no electrical issue using radials in your M-8, even though they may look a little different installed.

I suspect that you could use more than 15uF, but the global negative feedback does come back through the cathode circuit and this cap is involved, so you should stick close to the schematic value.

The knock on buying NOS electrolytic caps is that, like the "O" stands for, they're old. Even without use, there is concern that they can dry out over the years so many folks steer away from them.
 
Hello Dave451, I tested the Vishay-Sprague 15uF capacitors that I originally received from Mouser and they all tested a little over 20uF. That is within tolerance. It is hard to know if some of the capacitor sellers are actually selling NOS units or current made units. I have tried to Google date codes of different manufactures, but to no avail. In restoring old cars, when someone said they had NOS car parts for sale my eyes would glaze over. Thanks for your help and thanks for taking the time answer my questions. David
 
No worries, David. Sounds like you're thinking about the right kinds of things as far as I can tell. Only one other comment: I think it's pretty likely that new production units from reputable suppliers like Mouser or Digi-key are fresh. Best of luck with your work and check in from time to time!
Dave
 
How do you like those Arizona Cactus caps on the Model 8? I use them in my Marantz 7 and they are absolutely amazing.

Not all tantalums are created equal. I restored a pair of Model 5's last year that use a similar circuit. In those I used the NASA developed wet tantalums, which are Vishay/Sprague 135D's.

My capacitor of choice now to replace conventional low voltage electrolytics and tantalums is the surface mount Rubycon MU, which is a polymer multi-layer film design. They are tiny and designed for high-end surface mount audio applications. They are available in 15uF 16V ratings from Mouser or Digikey.

To use them as a conventional cap, you would need to solder them into a SMD to through hole board as shown:

123241531_10223864427381437_3044275842518734372_o.jpg


They are expensive, but worth every penny, IMO.
 
Last edited:
Hi crooner,
I am curious about the SMD to thru hole adapters. Did a bit of searching but couldn't find the particular version you show for the capacitors.
Thanks,
John
 
I'll let you know when I get home from work. I had to get them through a specialized outfit here in the US.
 
You guys are awesome. Thank you so much for your help. To Crooner, I love the Cactus caps. They have a period look to them and they sound great. Currently, I left the original Blue-Grey can capacitors C16 and C20 on top of the chassis but bypassed them underneath. I am considering having Hayseed build some duplicates and painting them to match the originals. My next project will be my Marantz 7 but I have not decided what I want to do to it yet. Thanks again! David
 
Codecheck said:
... Previously, I rebuilt a Marantz 8 (not an 8B) with Arizona Cactus capacitors and Russian Paper in Oil capacitors. ...
David
Click to expand...

David, Which new capacitors (Cactus or Russians) did you fit for the 0.1 uF signal capacitors C7 and C8 (A&B) from 6CG7 to EL34? This is the only capacitor in the direct signal path and seems to be the one to optimize.

I am in the process of refurbishing my 8B. The amp recently recapped with Audiocap Thetas, but they have imparted a somewhat analytical presentation, that is not consistent with the sound we want from the legacy 8b. That said, I want to avoid purposeful coloration.
More here:
https://audiokarma.org/forums/index...age-power-supply-diodes.943416/#post-14456702

Thanks
 
You must log in or register to reply here.
Back
Top Bottom