It had to happen eventually... capacitor upgrade question for the Mainline

[JamieMcC]

Nice job and a enjoyable read thanks for sharing your experience with the mods. Its going to be a handy reference.

[Mike Ross]

I've been running the RTI 10uf 310VDC Teflons for around 200 hours. Sonic shifts were continual till about ~100hrs it seems. Its settled down quite a bit now, and I very much like the sound I'm getting. Great texture, solid punchy base, shimmering highs with no obvious roll-off; Very glad I picked them up. Let's see what the next ~300hrs. bring.

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.

[HF9]

Was TCTubes the only supplier of the RTI 10uF Teflon caps? They don't seem to be floating around anywhere else. I'm finally getting along to my own build after getting some other projects out of the way. I have a set of Jupiter 10uF 300V Flat Stack caps I'll be using, along with a pair of 0.1uF 600V that aren't much larger than the stock caps. Pretty excited as I've enjoyed using the Jupiters in other builds.

The 0.1uF caps are a little off in their rating as they were some odd stock from the manufacturer. 0.116uF. Assuming that's acceptable as many caps are +/- 20%.

[2wo]

The 0.1uF caps are a little off in their rating as they were some odd stock from the manufacturer. 0.116uF. Assuming that's acceptable as many caps are +/- 20%

That won't be a problem, might even be a slight plus...John

[Strikkflypilot]

Loquah, thanks for the great build reports and reviews!
I have already ordered the 10uF/400VDC XO Series Auricaps and the Mainline hasn't even been shipped yet:)
I read the XOs are something to look forward to.
Can't wait to get building

[Strikkflypilot]

When replacing the 10uF caps, do the inner foil leads connect to 15 and 25?

From studying the schematics, I am sure they do.

[Loquah]

When replacing the 10uF caps, do the inner foil leads connect to 15 and 25?

From studying the schematics, I am sure they do.

Sorry for the slow response! I've hardly been on this forum (or any lately). Did you get it all wired up yet?

[Strikkflypilot]

No worries.
I am building very slowly.
Just about to finish input wiring.
Will post some work in progress images
if I get around to it.

Edit : Just did:)
http://bottlehead.com/smf/index.php?topic=7463.0

[Loquah]

Nice one!

By the way, I checked my build (and discovered I got one of the Auricaps the wrong way around), and you're spot on about the red leads connecting to 15 and 25 - the same terminals where the red leads from the output transformers are connected

[Strikkflypilot]

Thanks Loquah, means a lot!

Was happy to see the transformer working to specs, and the attenuators are finally in there.
Today I received a black XLR connector so all parts are "in house".
I like the way the manual is chaptered so I can really think through the process before actually building. I believe it makes a good looking build. Will post as I progress.

[NightFlight]

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

Speaking of which, I'm seeing that initial startup voltage hit ~320-325V on the 10uF Caps for around 5 seconds or so.  Its a little disconcerting to watch. However I'm getting the impression that the rating for poly caps in general have a high margin. For example Auricap posts their stress and life tests here: http://www.audience-av.com/capacitors/PDF/Auricap_Specifications.pdf

Would it suffice to say that poly caps in general reflect this sort of rating/life margin?  I'm sure you haven't seen or plan to see any of these Dayton caps explode 

[Grainger49]

It is not unusual for the full B+ to appear on the output caps at startup.  After all, the tube is not conducting and it has nowhere to go.

Caps have AC ratings, DC ratings and surge ratings.  You are seeing the surge at startup.  Sadly most film manufacturers don't give surge ratings.

[Paul Birkeland]

Speaking of which, I'm seeing that initial startup voltage hit ~320-325V on the 10uF Caps for around 5 seconds or so. 

Capacitors are able to tolerate a voltage surge for some time at startup, which can be significantly above their rated operating voltage.  In the case of the Mainline, the 12AU7 will pull the B+ rail to +225V and the 6C45PI plate will pull down to ~150V.  Each tube will do this without the other in the socket.

[NightFlight]

I was about to drop on the April sale at pCX and grab a pair of 10uF flat packed Jupiter caps... I still may - this is a sickness after all. I've read great things about them. Plus, they look so cool.

Then while I'm mulling this over... suddenly my Mundorf Mcap EVO - Silver / Gold & Oil  decided to open up and let their presence be known. After a year of installation no less! I've never thought a cap could take this long to come into its own, but there  it is.  Or I could just be nuts. 

http://www.partsconnexion.com/prod_pdf/evo.pdf

Well not generally revered as a top flight cap, the idea behind Mundorfs EVO winding tech intrigued me.  Their not hideously expensive either. (Actually, Mundorf must have recently fixed that by releasing an EVO 'supreme' version - ha ha ha). So while not totally impressed with these EVO SGO and gearing up to do something about it - a year of listening goes by and a couple days ago I realize they must have just 'clicked' in to place. They'd been holding back the full picture this whole time (IMHO).

Goose-pimples showed up. Angels wept. Etc.

Maybe I'm nuts. Maybe the little bastards picked up on the threat of replacement...
But at this point I can't help but recommend them if you have to patience to break them in. A year! OY!

[ALL212]

Has anyone compared 10uf caps to something larger?  I think I read you can go up to 20uf.  I'm just talking value, not physical size or brand.

I'd like a bit more bass and if I go larger than 10uf in the quality of cap I'd like to use we're talking an investment. 

I'm not opposed to tacking on an 8uf or so but real estate under that hood is premium so I'm asking before I do something not so smart...