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February 27, 2021, 02:37:22 PM

Author Topic: It had to happen eventually... capacitor upgrade question for the Mainline  (Read 29395 times)

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Offline Loquah

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I'm just about to embark on some hot-rodding of my S.E.X. and it got me to thinking I should consider the Mainline next. Looking at it though, there aren't a lot of caps to play with as far as I can tell so I wanted to check if anyone can suggest any specific caps worth changing?

My first thought was the Dayton 10uF caps on the output tubes. Are these operating as output caps?

The only other caps I saw were the tiny yellow ones that bridge a couple of the pins on each output cap (I can't easily see them enough to provide a better description at the moment). Would these benefit from replacement with some nice Russian teflons?
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Offline Paul Birkeland

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The 10uF caps are the coupling caps.  They can be 10-20uF, and probably should carry at least a 200V rating.  (160V might work, but would really be pushing it)

The tiny yellow caps on the sockets are out of the signal path and implemented for silent operation.  There's a good chance that if you swapped them for something else, that alternate cap would not perform as well, and you would likely end up with a dysfunctional Mainline. 

The 0.1uF 400V capacitors on the center PC board can be swapped out as well.  They won't have nearly the influence that the 10uF caps have, and the available space on the PC board is somewhat limited.  You can help yourself out by using a 250V capacitor here, which will see more than 250V at start-up, but will operate at 225V otherwise, which I would consider acceptable.

-PB
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Offline xcortes

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Paul, i don't know the exact Mainline circuit but I know it's a spud so maybe instead of coupling you're referring to parafeed caps?
Xavier Cortes

Offline Doc B.

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Yeah, he means the parafeed coupling caps, that is, the caps that couple the plates to the output transformers.
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Offline xcortes

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Cm'on, you're usually not that diplomatic!
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Offline Doc B.

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You caught me on a good day. So how's that projector?
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Offline Loquah

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The 10uF caps are the coupling caps.  They can be 10-20uF, and probably should carry at least a 200V rating.  (160V might work, but would really be pushing it)

The tiny yellow caps on the sockets are out of the signal path and implemented for silent operation.  There's a good chance that if you swapped them for something else, that alternate cap would not perform as well, and you would likely end up with a dysfunctional Mainline. 

The 0.1uF 400V capacitors on the center PC board can be swapped out as well.  They won't have nearly the influence that the 10uF caps have, and the available space on the PC board is somewhat limited.  You can help yourself out by using a 250V capacitor here, which will see more than 250V at start-up, but will operate at 225V otherwise, which I would consider acceptable.

-PB

Thanks PB. The S.E.X. will be my test dummy before I move to the Mainline. I'll be sure to post impressions.
Check out my reviews on YouTube - https://youtube.com/c/passionforsound

Offline xcortes

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Slight issue with the ps board. Interesting enough the tubes have filaments that are heated by a voltage of, yes, you guessed right 6.3 volts! Mine has an issue and the voltage starts decreasing over time so the image starts fading. We diagnosed this over the weekend and Curt will send a new board. Not very different from debugging an issue with a tube amp :)
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Offline Loquah

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Wow. Any ideas on the cause?
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Offline xcortes

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Apparently a faulty trimpot.
Xavier Cortes

Offline fullheadofnothing

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Lachlan -
You're following that Dan and Xavier have thread-jacked this to be about CRT projectors and not Mainlines, right?
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Offline Loquah

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Lachlan -
You're following that Dan and Xavier have thread-jacked this to be about CRT projectors and not Mainlines, right?

Haha - no, I thought they were referring to the power supply board in the Mainline. Thanks for preventing further embarrassment on my part!!  :o
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Offline swich401

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How many 10uF caps would I be looking at replacing if I wanted to upgrade? I'm still waiting on my Mainline (and the manual), but I'd like to order the caps in before the Mainline kit gets here so I can put them in during the initial build.

For these 10uF caps, should I go with a lower voltage (e.g. 250V) or with a higher voltage (e.g. 400V or more)? How would that affect the function of the cap? the sound?

Think there would be any benefit to replacing the Daytons with 10uF 400V Mundorf M-CAP MKP Series ??

In your opinion, what are the best brand and/or type of cap? Metallized Polypropylene Capacitors? Paper In Oil Capacitors? Paper In Wax Capacitors? Polyester Film Capacitors?

Thanks!

Offline JamieMcC

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How many 10uF caps would I be looking at replacing if I wanted to upgrade? I'm still waiting on my Mainline (and the manual), but I'd like to order the caps in before the Mainline kit gets here so I can put them in during the initial build.

For these 10uF caps, should I go with a lower voltage (e.g. 250V) or with a higher voltage (e.g. 400V or more)? How would that affect the function of the cap? the sound?

Think there would be any benefit to replacing the Daytons with 10uF 400V Mundorf M-CAP MKP Series ??

In your opinion, what are the best brand and/or type of cap? Metallized Polypropylene Capacitors? Paper In Oil Capacitors? Paper In Wax Capacitors? Polyester Film Capacitors?

Thanks!

Possibly a good idea to hold fire for a little bit longer as a couple of Mainline users have recently installed some rti 10uf 310VDC Teflons (still some available) initially made for use by Audio Research in their reference tube pre-amp. I am hoping we will get some feedback soon they have the potential/reputation to be a bit special. They should be a good way into the 500hr burn in that the Teflons require now.
« Last Edit: April 08, 2014, 08:10:06 AM by JamieMcC »
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Offline mcandmar

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Think there would be any benefit to replacing the Daytons with 10uF 400V Mundorf M-CAP MKP Series ??

Don't know much about the Daytons but the Mainline deserves much better than regular MKP series, i would want supremes at a minimum.
M.McCandless