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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 88

post #1306 of 7247
Quote:
Originally Posted by mordy View Post

 

Here is a picture of my newly acquired RCA 6J4 tube. There is a beautiful orange glow reflection from the heater at the bottom of the tube. I am running it together with the Sylvania 8532 tube, and they seems quite compatible with similar sound signature.

Somebody had complained that they had problems with microphonics with the 6J4 tube, but even tapping it directly with my finger their is no untoward noise.

 

I also had a problem with microphonic RCA 6J4. You might remember that I had a pair of Motorola 6J4, rebranded from RCA (post #1048, page 70) and one of them was microphonic. But looking on the bright side, only one of them was bad, so perhaps I should send you the good one and then you will have a good pair? :)

post #1307 of 7247
Quote:
Originally Posted by MIKELAP View Post

Dont know if this is of interest related to Sylvania tubes                     http://pax-comm.com/pa01039.htm                                                 http://www.audioasylum.com/cgi/vt.mpl?f=tubes&m=242045

 

Thanks for the link.

 

Why did Sylvania use the Leaf logo?

post #1308 of 7247
Wow, bored in a hotel and wandered into this section and found this thread. My Dad has been selling tubes for a few years now, it's cool visiting home and seeing his wall of tubes and the radios he has rebuilt. He said the Chinese have went nuts lately as 40% of his sales come from China now.
post #1309 of 7247

Scratch the notes about MKII issues. I'm beginning to think it's something wrong with my amp.

I put in a pair of previously silent GE 6676 tubes from a few months back and the right channel is still experiencing some level of buzzing.

I think I'm going to contact Little Dot about servicing this animal. I just need to make sure it happens reliably with EF91/92 tubes.

post #1310 of 7247
Quote:
Originally Posted by rosgr63 View Post

 

Thanks for the link.

 

Why did Sylvania use the Leaf logo?

It looks like an oak leaf and where do you see oak leafs you see them alot on military decoration  .Historically, the oak leaf is a symbol of endurance and strength. 

post #1311 of 7247

For 6AH6 tubes I need to strap pins 2 and 7, what the best method? Should I strap the socket or the tube itself.

 

has anyone made an adapter? If so how can I get a hold of one?

 

Anyone have any pics? I just ordered a pair of TS 6AH6WA.

 

I've been using a pair of Raytheon 6GX6 with 6N6P-IR power tubes which is a great combo.


Edited by mab1376 - 5/20/13 at 8:08am
post #1312 of 7247

In today's mail, I received two more pairs of 6AQ4, triodes, bringing my total to three pairs:

 

 

I received these about a week ago. They were manufactured in the Mullard Whyteleafe "A" factory in 1960. Notice the "Old World" D-getter. AFB tells me that this was kind of an experimental factory that made specific tube types in the 50s and into the early 60s. Eventually manufacture of these tube types was shifted to the Mitcham factory.

 

 

And sure enough, these Philips tubes were manufactured in the Mitcham factory in 1973. AFB's CV4070/6AQ4 were also manufactured in this factory at about the same time. Notice the O-getter

 

 

And a pair of Sylvania. I thought these looked very similar to the Philips, but still, imagine my surprise when I examined the tube codes and discovered that these too were made in the Mullard Mitcham factory in 1969!

 

These 6AQ4 proved quite difficult to find. In fact, I couldn't find any on eBay, and had to dig deeper into Google search to find other sources. In the end, I bought these sight unseen, knowing only the brand. I am a bit disappointed that the Sylvanias are in fact Mullards, but in the end, I think I got some pretty nice tubes. 

 

Now to find out how they sound.... Time to cut some pins and start burning....

post #1313 of 7247
Quote:
Originally Posted by mab1376 View Post

For 6AH6 tubes I need to strap pins 2 and 7, what the best method? Should I strap the socket or the tube itself.

 

has anyone made an adapter? If so how can I get a hold of one?

 

See Acapella's chart on page 77. There is a picture and directions on using a small stranded wire to strap pins 2 and 7 in the socket. Currently, this is what the vast majority of us are doing. That said, a number of people have ordered a set of socket converters to allow 6AU6, 6AH6 and simlar tubes to be plugged directly into our 6AK5 sockets with no wires. However, to my knowledge, no one has received these yet.

 

http://www.ebay.com/itm/1x-6AU6-to-6AK5-tube-adapter-socket-converter-/290917075011?pt=Vintage_Electronics_R2&hash=item43bc024843

 

My advice is to use a small wire for now, and wait until we have some feedback on these socket converters.

post #1314 of 7247

I had taken some pictures of my most recent triodes but forgot to ever post them...

 

So, here's the CV4070 (6AQ4) I got the other day, Mullard Mitcham-made, 1972, mil-spec, very clean looking. I gave these 20 hours of burn-in and found them to be very nice tubes, with great micro detail and extension but dry and lacking the kind of musicality and "magic" that I get with my favorite TS 6485. These are the loudest tubes I've tested since the EF91 family (mu=70) with a mu of 100 (a 6AK5 is 20, and even a 6J4 triode is 50, so we're pretty far from the original specs here). Anyway, I might give these a try again at a later point since they have such interesting characteristics, but for now I need to relax with "tubier" tubes lol... Like gibosi said, 6AQ4/EC91 are hard to find, and these are just as hard to get. They look the exact same as gibosi's Philips and Sylvania Mullard-Mitcham-made 6AQ4 btw.

 

 

Here are the new tubes I'm now burning in over some even newer Daft Punk music. CV5311, so "selected mil-spec" Mullard tubes (CV5xxx are supposedly selected CV4xxx, themselves mil-spec Mxxx, themselves premium EFxx on which the older CVxxx were based... Actually was able to test that back in my EF91 adventure days, where for example: EF91 < "EF91/6AM6"  < or = "6AM6/CV138" < M8083 = or < CV4014 < CV5377; and the CV4014  -or some CV4xxx types in general- were manufactured either in Whyteleafe in early days and in Mitcham in later times, which further complicates understanding the "hierarchy" of UK/Mullard tubes; in my experience though Mitcham-made (usually with O-getters) tubes were superior to (usually D-getter) Whyteleafe which were good but just different (larger and drier), at least for the EF95 and EF91 families where I tested it myself), Mitcham-made, so basically the best you should be able to get out of UK NOS tubes, but mil-spec or rugged doesn't always mean good-sounding as we've experienced.

 

At any rate, these are nicer on the ear than the French 6J4S I'd tried and the aforementioned CV4070. Interestingly, these have very loud volume -closer to EF91 or 6AQ4 high-mu types than other 6J4 triodes, even the Sylvania 8532W I tested but never reported on, or did I? I forget... They are also very bright-looking and light up like the 6AJ5 did, and are built like tanks, which makes me think that they are indeed very ruggedized and made largely over specifications -robust cathodes and heaters- to keep their characteristics after 1000-2000 hours. Right now, they definitely seem to have more "power" than they should...

 

 

Telefunken EH900S (6BY6 type), no diamond-on-the-base or gold pins, German "eagle" military symbol (strange...), USA label (stranger...), made in '77 somewhere; I have no idea who really made these and how they'll sound, but the boxes were definitely Telefunken.

 

post #1315 of 7247
Quote:
Originally Posted by gibosi View Post

 

See Acapella's chart on page 77. There is a picture and directions on using a small stranded wire to strap pins 2 and 7 in the socket. Currently, this is what the vast majority of us are doing. That said, a number of people have ordered a set of socket converters to allow 6AU6, 6AH6 and simlar tubes to be plugged directly into our 6AK5 sockets with no wires. However, to my knowledge, no one has received these yet.

 

http://www.ebay.com/itm/1x-6AU6-to-6AK5-tube-adapter-socket-converter-/290917075011?pt=Vintage_Electronics_R2&hash=item43bc024843

 

My advice is to use a small wire for now, and wait until we have some feedback on these socket converters.

 

Thanks, I'll see if I can give it a shot later, I have some 6AU6 tubes I haven't tested yet.

 

I also ordered the converters, but coming from Hong Kong I'll expect it to take about 2 weeks.

post #1316 of 7247

Hi G,

 

The "blue glass" is a Mullard give-away - I don't think anybody else made tubes with this feature. In addition, those little round plastic pin protectors were only included with Mullard tubes and an Australian Mullard clone that was inferior in quality.
 

post #1317 of 7247

 

Mordy, I didn't know that blue glass is an indication of Mullard manufacture. Back when I was rolling 5654 tubes, I wondered where these RTC 5654RT were made. As I understand, RTC was a French company that made some of their own tubes and rebranded others. However, I cannot find any manufactureing codes on these, so they have remained a bit of a mystery. So now it appears that these were likely made by Mullard?  But they sure don't look like any Mullard EF95 I have ever seen....

 

Oh, and none of these 6AQ4 came with those little plastic pin protectors... Maybe only Mullard CV series tubes came with these?


Edited by gibosi - 5/20/13 at 10:51am
post #1318 of 7247

Hi Mikeleap,

 

Thanks for the links. The third link provided the most information. One of my Sylvania tubes has a letter code L7V. The first letter is the month, with A being January etc. The second number is the last digit of the year it was made, and the V is a code for a Sylvania factory. So L7V translates into December 1957/1967 (take your pick) made in the V factory. Sometimes the letter "I" was discarded in a sequence since it looks too much like the number 1; then this tube would be made in November.

 

Other Sylvania tubes I own have the designations CH, ke     and ak         etc.

                                                                                   ARK        JBB

 

If anybody can decipher these letter combinations, please let me know. All the above tubes come in the same old style Sylvania yellow boxes.

 

Here is a chart that explains the different colors on the box flaps and tube print. One of my Sylvania 6AV6 tubes has red print instead of black print on the box flap, and the tube has red print. Oops, no warranty!

 

 

 

TUBE WRITING COLOR

BOX FLAP WRITING MEANING
Yellow Black Standard Sylvania Warranty
Red/Orange Red Distributor Warranty Only
Syl sells to dist for less
Sylvania absolved of warranty
Green Mil Box: Black
Export Box: Unknown
Military or Export
No Standard Warranty
The above table applies only to the Yellow boxes. In the old Green box days, standard writing was usually green.
The newer Philips/ECG tubes usually had blue writing.
post #1319 of 7247
Quote:
Originally Posted by gibosi View Post

 

Mordy, I didn't know that blue glass is an indication of Mullard manufacture. Back when I was rolling 5654 tubes, I wondered where these RTC 5654RT were made. As I understand, RTC was a French company that made some of their own tubes and rebranded others. However, I cannot find any manufactureing codes on these, so they have remained a bit of a mystery. So now it appears that these were likely made by Mullard?  But they sure don't look like any Mullard EF95 I have ever seen....

 

Oh, and none of these 6AQ4 came with those little plastic pin protectors... Maybe only Mullard CV series tubes came with these?


Gibosi, Mordy, RTC was part of the Philips -and therefore Mullard- group which may have shared technologies and definitely tubes between European plants. Although I have never seen EF95 tubes with blue glass, it doesn't seem illogical either, since the whole purpose of the process -like carbon-colored or silver glass- was to absorb the stray electrons that would otherwise make the glass more fragile over time. While the "blue" trait seems to be tied to Mullard, I'm not sure we can actually trace it back to a specific pattern in Philips tubes; it seems to just have been "selected" as a specification for some tubes made in Philips factories. Most Mullard EF91 types had blue glass until the 80s and mysteriously lost it afterwards, my CV4070 (6AQ4/EC91) and old-world EC91 have blue glass, and other similar Mullard signal tubes have it as well without any reason I can understand (on pentodes such as EF91, screening make sense, since the anodes don't cover the hole surface where electrons are sent from the cathode -hence the suppressor grid and blue or silver glass that "catch or absorb them- but on triodes like the 6AQ4/EC91 or 6J4 the anode literally encircles the cathode very close, so few electrons should be able to get through, and we still find blue or grey glasson some tubes).

 

So, basically, I wouldn't necessarily count on the blue glass trait or pin protector trait to determine a tube's manufacturer. Factory codes, on the other hand, are a pretty fail-safe way to know for sure, as gibosi pointed out for his "Sylvania" 6AQ4.

post #1320 of 7247

Hi Folks,

 

From the Oddly Enough column:

 

Came across a new use for old tube boxes:{$9.99 + $4.50 ship}

 

http://www.ebay.com/itm/2-Mullard-10M-Master-Series-EF86-6267-Tube-Boxes-Boxes-Only-No-Tubes-/261215479436?pt=Vintage_Electronics_R2&hash=item3cd1a7e68c

 

 

 

BTW, Mullard Millenium tubes was the British answer to Sylvania Gold Brand, GE 5 Star and Russian DR tubes which were all engineered to last around 10,000 hours.

 

OK, I found one Raytheon blue glass 5654/EF95 tube. (Made in France by RT=Mullard)

 

http://www.ebay.com/itm/1-x-Raytheon-5654-EF95-tube-made-in-France-Black-plate-Blue-smocked-glass-/380415849529?pt=Vintage_Electronics_R2&hash=item58928d3439

 

 

Other makers of blue glass tubes were Tesla and Arcturus, but here the glass is all blue, and not a band like the Mullards.

http://www.ebay.com/sch/i.html?_trksid=p2047675.m570.l1313.TR0.TRC0&_nkw=Blue+glass+vacuum+tube&_sacat=0&_from=R40

 

Have fun!
 

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