Tube Lab #41 Coupling Capacitors

Today we take a first look at Audio Coupling Capacitors, what they are, what they do and why they're so important for quality audio. And I clarify the specifications for the 6550eh tube.
Note the vintage GE 6550 is actually a rebranded Tung-Sol, much better, everyone loves vintage Tungs!
Link to my online store: valvesnmore.com/

[@tomcook5813]

I like the holes around the tube sockets, ventilation is directed straight up the tube element and handy for the plate cap 😊

[@tubelab194]

Yes we do as well! We use this method on all power tubes, it really works well and will hopefully give you the maximum tube life. And keeping the chassis cool should increase the lifespan of all capacitors as well.

[@thevintageaudiolife]

Thank you for the information, informative and interesting. My fave caps so far are the Polypropylene’s, in my opinion these cap's give me the most uncolored nutral sound.

[@luminousfractal420]

Keep hearing that

[@smith2924]

I’m one of the people who figured out the discount code 😂 thank you! Amp looks really solid

[@tubelab194]

Well done! I put the code in so long ago, I forget if it was for fun, or for a special purchase, but now it's sorta like a hidden bit of minor treasure!

[@user-hu4ez6ew2q]

@@tubelab194 HI Mr 👋. Solen bad capacitor, Audiophiles hate Solen! Audyn Q4 one of the best cheap capacitor and Dayton Audio PMPC capacitor have big love of people. And JB capacitors jpx supreme amazing capacitor! 👍

[@tubelab194]

@@user-hu4ez6ew2q Thanks for your comments, but I need to put my experience with Solen caps in the mix. As an audiophile, Kit Amp designer and builder, I listen to prototype designs and test music almost everyday - I also sweep new equipment and tubes, so have a full spectrum analysis to look at. And my experience with Solen black "fast caps", is they are very good sounding, with no sonic abnormalities (they don't colour the sound). What goes in one end comes out the other with all the detail intact. Are there better sounding caps? Probably, but for cost/sound/quality nothing I've listened to comes close.

[@user-hu4ez6ew2q]

@@tubelab194 HI Mr 👋. Maybe you know... 🤔, one Dutchman did a capacitors test.But I not believe him. There are several reasons for this, but this is a long topic that requires a separate discussion.I'm sure the Danish manufacturers bought this test. Danes are scammers! The most cunning people in the world are the Danes, believe Me Mr. For my opinion, best affordable polypropylene capacitors - JB JPX Supreme red capacitors, next Audyn Q4 Red caps and most popular afforable capacitors in world Dayton Audio PMPC. Plus Japan 🇯🇵 famous Rubycon company recently released good green polypropylene MPB series capacitors. One day need make test all this caps.. 🤔

[@nealsturges5879]

Outstanding job on the woodworking Jim ' do you guys do all the fabrication work also ? Great info also in the detailed information of all your many video series

[@tubelab194]

In a past life i was a furniture designer and fine cabinet maker, one of my grandfathers as well, in fact I still use many of his hand tools and still have his tool chest.

[@LawsonsStudio]

Your monoblocks are looking fantastic. I'd be interested in your opinion of using constant current sources in both tubes. I've read that you can improve ripple rejection and half THD. Especially on the 6j5.

[@tubelab194]

I'm just barely familiar with the circuit. So I can't comment on what it would do to the sound of the 6p7's. My listening tests continue, and yesterday I received most of a case of National Union 7193 driver tubes (cv6 American equivalent). They all date from 1942 and are built to an RCA design in a factory that eventually Sylvania would take over. Anyway they sound amazing! The Mullard cv6's sounded great, but so far these best them! My design philosophy is KISS and focused on building to circuits I mostly or fully understand, using as short a signal path as possible with the quality components. In the end it's all about the sound!

[@midnightraiin4035]

Neato i live in Long Island City. Used to be a manufactoring mecca

[@Gez492]

Only came across your video very recently Really enjoyed you video and the prototype looks really sweet! Can I ask a question or get your opinion on the "sound" of Capacitors. I get that the rating uF rating determines what frequencies get through and of course this is the essence of how speaker crossovers work, so why wouldn't it affect the audio spectrum even if its primary function as a coupling cap is to block DC as you say preventing a very bad day happening. So for me the Capacitor is indeed influencing or shaping the sound by filtering but what I'd like to know is how lets say two capacitors identically rated but made from different materials can sound different?

[@tubelab194]

Yes any capacitor can become part of a filter network, which is why I use higher values for coupling. Traditionally engineers calculated the value to filter or cut off the lower frequencies thinking this would eliminate possible problems in amplification. I learned from Paul at PS Audio, to set the value to a very wide band, this ensures no unintended cutoff of the music spectrum, and if a problem on the edge of the music spectrum presents then you can think about tightening up the value. In our experience, this is never required and we end up with lovely natural bass that extends down to ~20hz @ -1db! Because of the nature of how coupling caps are made and the materials used, it's possible to get a wide range of sonic results. We strive for a neutral sound, that is clean and clear of any distortion, subtraction etc., I think some of the attention paid to higher end caps is the EQ they impart, which is fine, so long as you realize what you are doing. One very interesting Kit Preamp design that we sell is the E80cc which is direct coupled with no interstage coupling cap, and the sound is amazing! If you're interested the schematic is under information.

[@Geoduck.]

I like the K40Y-9 PIO USSR surplus caps and good old Sprague Vitamin Q's as a coupling caps tough, inexpensive and sound marvelous. I have bought teflon caps from VH audio fantastic sounding but expensive. Jim, add a tight zip tie on the back side of those leads to prevent them from pulling out.

[@Dutchamp]

Like Jim said those holes are very tide fitting de wire. So why would anyone pull the wires. Though your idea isn't bad ofcourse. 😉

[@tubelab194]

What a simple and elegant solution! I've been pondering how to make this safe, well safer! Their's still high voltage present at the end of the anode caps! Thanks!

[@tubelab194]

@@Dutchamp correct the snug fit (accidental!) helps, but as a designer I always need to allow for someone doing something unexpected, like pulling on a high voltage wire! So a simple zip tie strain relief, clearly is the way to go!

[@Dutchamp]

@@tubelab194 tyraps rule tightness 😂

[@luminousfractal420]

​@@Dutchampoh nice, steel inners. Maybe i wont snap those ones 👍😂

[@loudspeakerchefOriginal]

Nedlab capacitors are very good for this application

[@Dutchamp]

Hi Jim I use mundorf supreme mkp caps 0,47uf 600v Love them and use audyn caps near the B+ at my tubes parallel on a electrolyte. I go for high quality affordable if you diy building or upgrading a existing amp. Sound is very open and a big stage. Nice video how you explain the schematic. Good work About the price that audyn cap you pay 30 dollars? I'm located in Holland and I buy those for a 8 dollars. Do you count the shipping cost with the cap?

[@tubelab194]

I bought them several years ago, and didn't take the time to look up the bill. So I probably paid more like $20usd, but with shipping from the US and a terrible exchange at the time, maybe it ended up at $30!

[@Dutchamp]

@@tubelab194 the cap cost about 9,59 dollar maybe you bought more of them. Still for audyn cap it's a bit pricy. Like I use mundorfs and they sound even better the price is a little bit higher but sound 50% better.

[@MartyFavento]

Hi Jim! Which capacitor would work best in guitar amplifier to push out nice creamy mids and have a great headroom? :) Keep up the good work! love your vids!

[@tubelab194]

I have zero experience voicing guitar amplifiers, so can't offer any advice other than to try some different makes of coupling caps and see what sounds best!

[@MartyFavento]

@@tubenoobie2694 I have one Orange drop inside my guitar electronics and did a great difference :) sometimes you have something good on you without even knowing, Ill get more Orange drops to update my amp :)

[@dumbdickler670]

Depends on the circuit and your level of gain, but a good starting point is 0.022uF coupling caps In terms of "brand" or whatever, Mallory 150s are great. Sozo caps too, but they're much more expensive

[@davidnguyen5028]

I need to change my existing coupling capacitors from .02uf 600vcd to .01uf 800vcd, is this going to drastically change the sound of my push pull EL84 stereo amp?

[@tubelab194]

No that's a very minor difference. BUT coupling caps are rarely used at so low a value as 0.01uf, maybe in a low fidelity antique amp. We use 1.1uf and 2.2uf for all our coupling circuits. The reason we couple with such high values is the capacitor will make a high pass filter in circuit, so you want to make sure you include all the bass frequencies down to at least 10hz and preferably close to 0hz. In designing our circuits we couple "very wide band" and only trim the high pass filter if needed.

[@davidnguyen5028]

@@tubelab194 Thanks! My amp came from a record console so it’s really old. The schematic shows 20,000 mmf. Isn’t this .02uf? I just so happen have some orange drops at .01 uf on hand.

[@tubelab194]

@@davidnguyen5028 mmf is an old notation for pf, so correct .02uf, however as i previously mentioned this value is probably too low for coupling the entire frequency range for hifi. Back in the day, manufacturers limited bass response on records and in home audio equipment deliberately because it couldn't handle the full frequency band (and they also didn't see any need for wide band audio reproduction). I'm in no way an expert on rebuilding old equipment, but I'm sure you could find a dedicated Fb group to help out. It would be a good thing to upgrade the specs of an older unit. Your ears will thank you.

[@davidnguyen5028]

@@tubelab194 This helps convince me to go with 0.2uf, thanks!

[@Jagman5]

@@tubelab194 Love your explanations here, thanks! But I’ve two major questions on that: If you go with higher capacities around 1.1uF would you not make the amp a bit slower (that’s what experts tell me) for a frequency you can’t play the music anyways (

[@briansmith9698]

Tube Lab how good quality are Russian paper oil capacitors? I have old tube radio recap thinking about using Russian paper@oil capacitors just afraid of leaking. I have heard Russian paper capacitors are really good quality.

[@tubelab194]

I have some in stock and have used some in prototype builds, but i think a lot will depend on the plant and date of manufacture. The problem is the newer the cap the better, But you really don't want anything made in post USSR, so nothing made 1989 or later - manufacturing quality lowered substantially for many electronic items - as they tried to reduce costs and substituted inferior raw materials. So in our Kit Amp business we decided to go with one quality manufacturer (Solen), for all coupling caps.

[@briansmith9698]

@@tubelab194 What about old USSR paper oil Capacitors from 60s 50s 70s? What does glass ends mean?

[@briansmith9698]

@@tubelab194 Thanks check out your website

[@tubelab194]

@@briansmith9698 presumably they cast glass to close off the ends, remember all capacitors are some kind of roll or fold of material. Lots of different methods and materials to make them.

[@briansmith9698]

@@tubelab194 Thanks I got get more of them for the tube radio I try Solen also I can have the can capacitor custom made theres a site makes them I bought some also from tube Depot because I bought stuff from them in past quality is good.

[@moodyga40]

sozo capacitors i found to be good