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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 380

post #5686 of 6943
Quote:
Originally Posted by mordy View Post
 

Just wondering - what is the purpose of the metal covers for the tube?

 

Does the C3m tube require a different voltage? Seems it is less expensive than the C3g.

 

 As mab1376 says - 20V. And apparently also an excellent tube, but not the frame grid and gold pins of the C3g. Gain also seems less, and pin-out is different...so, given these caveats, certainly would appear a good candidate for those with external power supplies - if the price is right.


Edited by hypnos1 - 3/31/14 at 9:23am
post #5687 of 6943
Quote:
Originally Posted by gibosi View Post
 

 

From what I have read, "VT-231" is nothing more than an inventory number used by the US Navy during WWII. All you can really infer from this designation is they were produced in the 1940's in support of the war. Evidently, they are identical to 6SN7GTs made during the 1940's for civilian use.

 

My impression is the Sylvania VT-231 is prized by those who combine more than one 6SN7 together to counterbalance deficiencies in each to achieve a desired sonic signature. But as your C3gs are very linear, and likely have no significant deficiencies, I believe they require an output tube with more balance than the Sylvania. If you are still interested in trying old-stock 6SN7, I would suggest a pair of Raytheon VT-231. There are two versions, and the one with 2 free support posts and flat plates seems to be preferred over the other. Or a pair of Tung Sol "Mouse Ears." In my experience, both of these have pretty good balance.

 

Thanks for the info, gibosi. You certainly do a good bit of reading on these subjects!

I have to admit that I am being rather 'picky' in my appraisal of the Sylvanias...with tracks heavier on the electronics and without too much treble emphasis, they sound really exciting...so it could well be a case of swapping around to suit...it surely is asking too much to expect a tube to give everything...Possibly a real CV181/ECC32 just might get even closer to perfection (for my ears, anyway), but at their prices - if you can find them at all - they are a non-starter! So I think I shall keep with my CV181/6SN7 hybrid...for now, at least...

post #5688 of 6943
Quote:
Originally Posted by hypnos1 View Post

 

 

 

An excellent tutorial! I am bookmarking this page to use when I finally get around to purchasing a pair.

 

Cheers

post #5689 of 6943
Quote:
Originally Posted by gibosi View Post
 

 

An excellent tutorial! I am bookmarking this page to use when I finally get around to purchasing a pair.

 

Cheers

 

Thanks, gibosi - took me a good while to put together, but hope I covered most elements and that it may prove useful to you in the future (and perhaps anyone else who may be tempted to tread this path).

post #5690 of 6943

Hi,

 

As you all know, burn-in is a part of life using vacuum tubes. Found a free burn in recording that covers most bases. It is intended for headphones/ear buds, but sounds eminently suitable for tubes as well. The site seems to offer good advice as well.

 

https://www.jlabaudio.com/index/burn-in

post #5691 of 6943
Quote:
Originally Posted by hypnos1 View Post
 

 

Thanks, gibosi - took me a good while to put together, but hope I covered most elements and that it may prove useful to you in the future (and perhaps anyone else who may be tempted to tread this path).

 

Thanks much for the tutorial, I'm loving these more and more with time.

 

With my super sensitive T70's I heard a little bit of a background buzz, but with my HD650's its dead silent.

 

I haven't tested with the T70's again after some burn in, hopefully its gone.

 

Thanks again.

 

Also those washers may connect the shield to the outside metal base for reduced hum: http://www.audiofaidate.org/uploaded/baldo95/C3g-C3m-info.pdf


Edited by mab1376 - 3/31/14 at 12:20pm
post #5692 of 6943
Quote:
Originally Posted by mab1376 View Post
 

 

Thanks much for the tutorial, I'm loving these more and more with time.

 

With my super sensitive T70's I heard a little bit of a background buzz, but with my HD650's its dead silent.

 

I haven't tested with the T70's again after some burn in, hopefully its gone.

 

Thanks again.

 

Also those washers may connect the shield to the outside metal base for reduced hum: http://www.audiofaidate.org/uploaded/baldo95/C3g-C3m-info.pdf

 

My pleasure mab - glad to be of help. And am also glad you're finding that they are developing nicely...just wait 'til the 50 hour mark!

 

I would suspect that buzz is more to do with the adapters, but whatever, I do hope it disappears completely...(or perhaps the C3gSs are showing up something in the power tubes? Time should tell...Me, I had only deathly silence in the background - 650s again - with just the slightest 'ssshhh' with the volume at max and no music playing. But that, even, all but disappeared when I changed from the 6N30P-DRs to the Psvanes).

 

Interesting re the washers/gaskets...I removed the metal base in my permanent adaptation, and no hint of hum...but then again, there seem to be so many possible causes for hum!

 

Enjoy those little (well, not so little!) treasures...

 

Cheers

post #5693 of 6943

Received a pair of Ken-Rad VT-231 today. These are often costly so I have been waiting for a good deal to pop up on eBay. Even though these look rather different, they are the same tube and sound identical. I suspect many bidders were put-off by their mismatched appearance, which was to my benefit. :) 

 

The black glass seems a tad bit taller and was manufactured in June, 1944, and the shorter, clear glass, January, 1945. From what I have read, GE took over the company sometime in 1945, and the later, GE/Ken-Rad tubes don't seem to get much love. You can tell the original Ken-Rad from the later GE/Ken-Rad by the orientation of the plates. The original Ken-Rad has "staggered" plates. That is, while the plates are parallel, they are mounted between the micas at an angle. You can see this quite easily from the top. The later GE/Ken-Rads also have parallel plates, but they are mounted parallel to the edges of the micas.

 

This tube is considered to be the "Bass Champion" of the 6SN7s, and I can certainly attest to that. The mids are neutral with a bit of sweetness, and the highs are quite nice and extended, but not as smooth and airy as the Sylvanias. All in all, a very nice tube.

 

 

"Staggered" plates

 

post #5694 of 6943

Hi,

 

Was re-acquainting myself with the famed Mullard M8100/CV4010 tubes. Actually, they sound very nice with my 6SN7 RCA drivers. Took a picture and discovered the ephemeral mysterious blue light that sometimes appear with tubes:

 

On this picture you can also the thin heater wire on top of the mica that separates this tube from the rest.

 

Here is a fancier picture of the blue light phenomenon:

 

http://www.jacmusic.com/techcorner/ARTICLES/English-neu/blueglow/807-3.JPG

 

For further study (and more confusion) about what this is see this link under Type 1:

 

http://www.jacmusic.com/techcorner/ARTICLES/English-neu/blueglow/blueglow.htm

 

Good night!

 

Yep - I picked the right word:

e·phem·er·al
əˈfem(ə)rəl/
adjective
adjective: ephemeral
1.
lasting for a very short time.
 
synonyms: transitory, transient, fleeting, passing, short-lived, momentary, brief, short;

Edited by mordy - 3/31/14 at 10:22pm
post #5695 of 6943

Hey mordy those adapters looks nice.

post #5696 of 6943

Hi i luvmusic2,

 

There are actually 2x2 adapters. Here is the first one that allows you to put an octal tube into the Little Dot MKIII.

http://www.ebay.com/itm/221065459067?_trksid=p2055120.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

 

However, the decorative rings around the tube sockets do not allow these adapters to go inside the socket since the adapters are too wide to fit inside the ring. For this we need an extender or socket saver:

 

 

This set fits inside the ring. http://www.ebay.com/itm/2PCS-9-PIN-vaccum-TUBE-SOCKET-SAVER-FOR-12AX7-12AU7-ECC82-ECC83-tube-audio-amps-/251350602537?pt=Vintage_Electronics_R2&hash=item3a85a9d329

 

Spending around $35 incl shipping for these four adapters allows you to use any 6SN7 tube (and 6SL7) in your LD MKIII. These tubes outclass the 6N6P family of tubes and to boot are plentiful and very inexpensive.

 

There is a lot of hype about the 6SN7 tubes, and certain types command very high prices. IMHO I would not bother with these but instead buy any garden variety Sylvania or RCA tube. Just plug them in and enjoy delicious, full bodied sound! In addition, these tubes are well built and are supposed to last a long time.

 

Another added bonus I noticed is that my LD amp does not even break out in a sweat with these tubes and the amp is cool to the touch. It has to be added though that I am using another 6SN7 as driver with it's own power supply.  The tubes run hot, but the amp is not even warm.

 

And then there is the ephemeral Blue Light......


Edited by mordy - 4/1/14 at 8:02pm
post #5697 of 6943

Here MIKELAP is a nice tube for the little hybrid amp. Thanks!

:beerchug:

post #5698 of 6943

Hi TD,

 

The light on the picture is a LED light and not the blue glow. The following quote is from a 1960's Sylvania publication:

 

"Blue Glows are not tube detriments per se. They are, however, suspects in the eyes of many receiving tube users for lack of a full understanding of their origins. There are several types of Blue Glow which can be described as follows:

Blue glow FLUORESCENCE (Photo 1)- this type of glow is usually violet in color and most noticeable around the inside surface of the glass bulb. It is most pronounced on power tubes and is the product of electron bombardment of the glass taking place within the tube. It generally has no adverse affect upon receiver performance, and in fact, tubes displaying this phenomenon are particularly good with respect to gas content."

 

http://www.thetubestore.com/Blue-Glow-Photo-1

 

Quote: "Hey, you'd be blue too if you smacked your head off a piece of glass a few billion times thicker than you while traveling at the speed of light."

post #5699 of 6943

Hey mordy!

 

I was just showing MIKELAP the 6BQ7A he sent to me in use with the hybrid amp, the LED under the lamp is actually white but appears blue in the camera.

 

 

This is the Blue Glow that I like from Mecury Vapour Rectifiers.

post #5700 of 6943

Hi TD,

 

"MERCURY VAPOR HAZE - is a blue-violet glow associated with those tube types which rely upon mercury vapor for proper operation. In such cases, the blue glow should be evident indicating proper operation."

 

To be specific, the Blue Glow is not the same as the mercury vapor haze; the colors and origin are different.

 

http://www.clarisonus.com/blog/wp-content/uploads/2008/03/mv_rectifiers.jpgTo compare:

http://www.jonikazategi.com/wp-content/uploads/2013/12/5-Integrations-That-Will-Amplify-the-Power-of-Your-Lead-Nurturing.jpg

 

As you all know, an expired tube turns white:

 

http://2.bp.blogspot.com/-pkhawQtDFTE/UBMhZc1yIJI/AAAAAAAAOXo/q3hh1Hq3i1c/s1600/skeletubearmy.jpg

 

 

I guess that too much much tube rolling drive some people crazy.....

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