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AirTight ATM-300 - new Coupling Caps

So I want to replace the coupling caps in my Airtight 300B amp. The original ones are $5 Sprague orange drops. 0,1uF interstage caps between input tube (12AU7) and driver tube (12BH7A) and 0,47uF between driver tube and 300B.

I love the amplifier, it is very resolving and airy with great soundstage separation. However I miss some body and fullness, and tighter bass, hope new coupling caps can help with this. I like a natural sound with lots of body and texture, good detail and a tight and deep low end.

I have read alot of forum posts and narrowed my choices down to these 3;

Duelund CAST cu sn tinned copper

Jupiter copper foil paper and wax

V-cap ODAM

I have read that some capacitors are best used in lower voltage applications and others are better in higher voltage applications, so I am open to using different brands in interstage/300B coupling. 

Please share your experiences, impressions and recommendations. Not necessarily with the Airtight, but preferably used as a coupling cap.

rubjel
rubjel OP
16 posts
 

@salectric great post, thank you :)

My memory may have mixed it up with another cap wrt thin sound.

Reliability is definitely of high importance, the V-cap Cutf is on my list!

Would the CuTF fare well in both interstage and coupling? I read that some caps are best for Xovers and not so good sounding in electronics. And some even in interstage vs coupling and vice versa.

Can you please share your thoughts about the CuTF vs Duelund CAST tinned copper? Bass firmness is of high importance to me, since tube amps tend to be a bit wooly in the bass, don't want to accentuate this with the wrong coupling cap.

Tone density is also important to me. I would't necessarily say the AirTight is thin sounding, but I feel it has more focus on detail and transparency than tonal density and fullness/weight. Maybe the Jupiter copper would improve this aspect?

rubjel OP
16 posts
 

@gareents very interesting, thanks for sharing!

May I ask why you chose Multicap? This brand has gone under my radar, never heard of it before.

Did the sound become fuller, did tone density improve?

When you say it got more neutral, in what way do you think it deviated from neutral in it's original form?

johnss
683 posts
 

@rubjel used them in two locations. Interstage coupling and as PS filters on the input PS caps. 

All were excellent caps. The Dueland and Jupiter are both very organic sounding with huge instrument depth and placement. The V-caps were also quite good. Maybe a tad less of the organic sound of the other two. 

Just to make sure we were not imagining sonic differences we switched back to a typical but good plastic film cap. Holy cow, was a huge downgrade in sonics. 

There were four of us in this cap experiment. Wanted to make sure we got input from everyone. Did not try these caps on any SET amps all were P-P. The amps we ran the trials on were VAC, VTL and ARC amps. The first two were fully differential.  

If you are using the stock plastic film caps now, you will get a huge smile with a switch to any of these better caps. 

rubjel OP
16 posts
 

This is gold @johnss, exactly the kind of info I'm looking for!

So better quality input PS caps will also provide better SQ, this will get expensive :)

Your comment about Jupiter and Duelund being more organic than V-Cap is very valuable, as this trait sits high on my priority list! 

Just to be sure, the Duelund CAST was the tinned copper or the regular copper?

Very encouraging words, I can't wait to install new caps :)

gareents
80 posts
 

MultiCap has now become Reliable Capacitors now owned by Wilson Audio (https://www.reliablecapacitors.com)

MultiCap is a special design of capacitor - each individual capacitor being a bundle of smaller capacitors. Wilson Audio obviously is a big user.

Sound improvement was denser while at the same time also being more detailed.

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