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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 276

post #4126 of 10574
Quote:
Originally Posted by Audiofanboy View Post
 

Turns out that after looking at a gazillion other E188CC tubes on google and ebay, code VR2 means that these were part of a batch made in 1960, since any tube made later has a higher change code (actually, almost all the Heerlen-made E188CC you find have VR6 to VR9 codes and were made in the mid to late 60's, so much later). But what's even better is that tubes with the VR0 (first batch ever) or VR1 are the famous very early late 50's production with either a D-getter or a folded D-getter (= extreme prices); almost prototype-like tubes in a sense. So the VR2 tubes should essentially be the first batch of large O-getter E188CC tubes to have come out of Heerlen (give or take a few months). And as gibosi and I realized with the US Amperex 6922, the earlier the better, and those VR2 are pretty early!

 

This is good information to have. I have a single Heerlen-made Dario VR2 coming to me from France. (It is taking longer to get a tube from France than from the Ukraine! It was shipped on November 11! lol). Tube code: VR2 40H3. (And of course, since the Heerlen delta character is not readily available on most computer keyboards, many vendors use the number 4). I knew from the change code of 2 that it was early, that is, August, 1960, rather than 1970, and I would guess that your "PO" tubes are even earlier. I am hoping to have it next week and really looking forward to seeing how this tube compares to the US-made Amperex.


Edited by gibosi - 12/1/13 at 6:12am
post #4127 of 10574
Quote:
Originally Posted by gibosi View Post
 

 

This is good information to have. I have a single Heerlen-made Dario VR2 coming to me from France. (It is taking longer to get a tube from France than from the Ukraine! It was shipped on November 11! lol). Tube code: VR2 40H3. (And of course, since the Heerlen delta character is not readily available on most computer keyboards, many vendors use the number 4). I knew from the change code of 2 that it was early, that is, August, 1960, rather than 1970, and I would guess that your "PO" tubes are even earlier. I am hoping to have it next week and really looking forward to seeing how this tube compares to the US-made Amperex.

 

Good timing lol! So, someone agrees with my reasoning at least; always reassuring.

 

Yeah, what's odd about the date codes on my pair is that weird "PO" (or probably "P0", looking at the pictures again, which is even weirder since the third character should be a letter between A & L for the month) after the delta symbol. It really almost sounds a prototype code or somekind of "special" date code.

 

At any rate, 1960, and probably mid-year, since I've seen VR3 tubes with delta 0 codes, and VR1 tubes also with delta 0 codes, meaning that the VR2 code was short lived and sandwhiched between two other codes in 1960.

 

Quote from random lad on google: "The first line VR1 code signifies the first revision of the E188CC tube after the original best ever sounding VR0 version. The VR0 version appeared in December 1959 to January 1960, with the VR1 revision coming into existence thereafter in February 1960."

 

VR0 definitely has a D getter. All the VR1 I've seen have a D-getter (possibly folded D), and I assume that there were no changes in production without making a different batch. So, VR2 should be the first O-getter batch. I've seen VR1 with delta 0C codes, so at least from March 1960 onwards. And I found an auction with two VR2 and two VR3 tubes, coded either VR2 delta 0J2 or VR3 delta 0J3, so change between VR2 & VR3 batches should have been during mid-october 1960. So, yeah, a VR2 E188CC made in Heerlen should be dated sometime in the middle of year 1960. Fweew! Glad that's settled.
 

Hopefully, I should get my tubes fairly quickly, since they're in France in the first place (though it often takes as long to get tubes within the country as shipped from Canada, either due to the seller's laziness or due to unpredictable patterns in the French postal service; usually just seller laziness syndrome though...). If your tubes are taking 3 weeks to get to the US from France, I would start to, perhaps not worry, but at least inquire as to their whereabouts. 10 business days should be more than enough between two developed nations... In theory...

 

Edit: Color me surprised, there are more mystery (actually clearly identified) VR2 delta P0 E188CC out there. And pretty close too lol, since it's here on head-fi! Not that the people there had any better ideas to make sense of the the "P0" code...

 

http://www.head-fi.org/t/633006/aune-t1-usb-tube-dac-amp-discussion-thread-see-first-post-for-faq/2850


Edited by Audiofanboy - 12/1/13 at 8:14am
post #4128 of 10574
Quote:
Originally Posted by Ctritical Bill View Post

The heater voltages are very close to 6.3v . I live in 240volt land where I measure 238v at the wall and the Little Dots are designed for 220v so if the heater power supply were unregulated I would expect a much higher measured heater voltage. Several pages back someone showed a photo of the transformer and the driver tube heater windings were 6.6v @ 1 amp so looks like some sort of regulation is taking place. A good thing.
 

Nice work Ctritical Bill.

 

There is NO regulation on the filament windings, all 4 pairs of 6.3V wires go straight to the transformer. The primaries are listed as 120+120 so in series it would be 240V and that would fit fine with your 238V.

 

If you've missed it earlier and can possibly be of any use. Here is the "Very Rough" schematic I made of the LD MKIV and it's power supply section, only the left channel is shown as it was the easiest to follow the traces for and the right channel would be an exact mirror image.

(Don't forget to click on "Original" and click the picture again to get the maximum size before you right click save)

:beerchug:


Edited by TrollDragon - 12/1/13 at 8:14am
post #4129 of 10574

Hi Ctritical Bill,

 

I just got the same breadboard as you. I am new to soldering. How do you best solder in the leads where the resistors are supposed to be?

 

What kind of feet are you using? Golf tees?  I found little pieces of self stick foam that I cut to size and put underneath. Also, in order for better heat dissipation by the tube on the breadboard, I moved my LD back on the shelf and placed the adapter in front of the amp on little pieces of wood and foam.

post #4130 of 10574
Quote:
Originally Posted by vic2vic View Post
 

 

I'm quite interested on this mod (I own an LD MK II). Any suggestion for a replacement jack ? I was thinking about the Neutrik one, but that's actually the one you removed :o


Hi vic2vic.

 

From what I can see in the pics of the MKII your socket is different to mine on the IV SE, so I'm afraid I don't think I can be of much help to you if you intend to keep with the plug/socket combo...my mod was to remove the plug anyway and solder the cable direct to the board inside the amp.(which I can understand might not appeal to everyone, as of course that is then a semi-permanent arrangement if further changes are on the cards re headphones...although not TOO much of a hassle to re-do if necessary!).

 

One point I must make, however - doing away with the 'choking' effect of the plug & socket, plus inferior cable from the board has had an unforeseen consequence...the increased frequency range is showing up any over-exuberance by the recording engineer in the treble department! Something my pure silver cables are especially prone to do sometimes. But then again, I would much rather have the FULL sonic experience, warts and all, than something that 'tames' certain aspects of the studio's preferences/poor equipment!

post #4131 of 10574
Quote:
Originally Posted by mordy View Post
 

Hi Ctritical Bill,

 

I just got the same breadboard as you. I am new to soldering. How do you best solder in the leads where the resistors are supposed to be?

 

What kind of feet are you using? Golf tees?  I found little pieces of self stick foam that I cut to size and put underneath. Also, in order for better heat dissipation by the tube on the breadboard, I moved my LD back on the shelf and placed the adapter in front of the amp on little pieces of wood and foam.

 

Yes, I am pleased I got these boards as they are very versatile, you can use 9 and 7 pin sockets with them too. Also they look much better than my previous attempts.

I just cut some short pieces of wire and soldered them across just one of the links. The links are joined in pairs so only necessary to put in one link.

The feet are computer motherboard standoffs that I had lying around, just the right size.

I thought about putting the board at the front but the headphone cable is in the way on the MK111 but raising it up would get over that problem. I think it would look neater that way.

post #4132 of 10574

Hi All,

 

Here is a report of my first octal tube, a National Union 6SL7GT probably from the 1950's. Since my 6AK5 days I always thought that National Union was a sister brand to Tung Sol since they were both manufactured in the same area in New Jersey. (Newark, Orange)

 

So I thought that I snagged a bargain Tung Sol that just squeezed in at my $8 limit including shipping. A little research seems to indicate that they were two different factories and I could not find any information that Tung Sol acquired National Union (not to be confused with National which was the earlier name for the Japanese Matsushiita).

 

Here is a picture of the prototype octal flying adapter. The main reason I placed the tube in front of the amp was for heat dissipation and that the socket with  6SL7 to 12AX7 adapter + tube was too tall to fit on the shelf on top of the LD amp. I will try to get a more "professional" set up with the new breadboard on the right.

 

Now about the tube:

 

 

 

 

 

The only identification letters on the the tube are YT on the blackened glass, and KC on the base. KC  = December 1953? Would appreciate if anybody has information, as well as information if there is a link between NU and TS.

 

The tube was sold as used and tested "good", whatever that means. The sound has improved over the 50 hours that I am running it which makes me believe that perhaps this tube is new.

 

The first impression listening is that that it requires higher gain than the 12AX7/6DJ8 families. Second impression is that the bass and treble are very nicely extended, similar to the Voskhod 6Sh1P-EV, but much nicer and sweeter than the Voskhod. Third, this tube runs very cool and never gets hot to the touch.

 

After extended burn in my impression is a very sweet tube with no harshness at all in the treble, especially listening to strings. Cymbals are technicolor shimmering, and the low bass is fat and authoritative. The mid range is very sweet and voices are very natural.

 

On the con side there is a lack of quickness, attack and slam in the mid bass and not the greatest etched detail, especially compared to the Amperex A-frame 6DJ8. However, it makes it up in the overall sweetness and overall pleasant, beautiful and non fatiguing sound. A keeper.

 

Don't know why the octals are more expensive than most of the other tubes we have tried. Perhaps people think that bigger is better, and these tubes certainly are much bigger the 7 and 9 pin tubes suitable for the LD MKIII. Too, it could be that they are more rare, being older and production ceasing earlier than the other smaller tubes.

 

Would appreciate help in a possible TS-NU link, and the dating of this tube.

 

Happy tube rolling!

 

 

 

 

 

post #4133 of 10574

Hi TrollDragon

 

Thankyou for posting the schematic, makes it easier to see what is going on. I would really like to get voltages with stock 6AK5 tubes so that we have a reference for the ideal settings.

I am still surprised at my heater readings as the 6SL7 only draws 300ma and the transformer is 6.6v @ 1 amp but I am happy with that as the heaters aren't being over-volted.

Have you been able to measure the B+ ? I guess it must be a bit over 200v but if we knew for sure everything else could be calculated.

 

I have been thinking more about these 6SL7 tubes and although they sound very good in the LD (especially the soundstage) I think they are very unsuited. In this sort of design with a push-pull output stage, the plate voltage on the driver tube should be half the B+ to balance the drive to the output tubes. The 150-160v I am measuring is way out so one triode of the output tube is going to be overdriven. Also the grid voltage at about 1v is too small to prevent clipping and will lead to distortion which I think I am hearing in the treble.

The datasheet I have of the Brimar 6SL7GT quotes the operating characteristics as plate voltage 250v and grid voltage 2v so you can see how far out from ideal we are.

post #4134 of 10574
Quote:
Originally Posted by Ctritical Bill View Post

 

Thankyou for posting the schematic, makes it easier to see what is going on. I would really like to get voltages with stock 6AK5 tubes so that we have a reference for the ideal settings.

I am still surprised at my heater readings as the 6SL7 only draws 300ma and the transformer is 6.6v @ 1 amp but I am happy with that as the heaters aren't being over-volted.

Have you been able to measure the B+ ? I guess it must be a bit over 200v but if we knew for sure everything else could be calculated.

 

I have been thinking more about these 6SL7 tubes and although they sound very good in the LD (especially the soundstage) I think they are very unsuited. In this sort of design with a push-pull output stage, the plate voltage on the driver tube should be half the B+ to balance the drive to the output tubes. The 150-160v I am measuring is way out so one triode of the output tube is going to be overdriven. Also the grid voltage at about 1v is too small to prevent clipping and will lead to distortion which I think I am hearing in the treble.

The datasheet I have of the Brimar 6SL7GT quotes the operating characteristics as plate voltage 250v and grid voltage 2v so you can see how far out from ideal we are.

 

And in addition to the 6AK5, I think it would be useful to have similar measurements for the EF91 and EF92, as these are very different than the EF95. Given the enormous variety of tubes that I have successfully used in my LD over the past year, my impression is that the LD was designed to easily accommodate a very wide range of tubes.

 

Re: Octals.... I have a Tung-Sol 6SU7GTY and a Sylvania "Chrome Top" 6SL7WGT, in other words, two of the best, and I have not heard any high frequency distortion with my ears (admittedly old) and gear......

post #4135 of 10574
You are most welcome Ctritical Bill. I didn't measure it but I will pop the back of my amp later and see if I can get a reading for you. The board is a real pain to remove from the case on the MK IV, so I should be able to reach a test point with a wire on a probe.
beerchug.gif
post #4136 of 10574

Actually, thinking more about this, I can calculate the B+ from my measurements and the value of the plate resistor from your schematic. And the number is ....... 200v almost exactly.

So the plate voltage on the driver tube really needs to be down around 100v which is close to ideal for the 6DJ8 as it happens.

post #4137 of 10574

Can a 6SC7 tube be substituted for a 6SL7 tube? What is the difference/advantage of a metal tube vs a glass tube?

post #4138 of 10574

Could any of these steel and glass octals be used with the Littledot i have and old tube radio and i use these tubes 6AC7, 6SQ7, 6SK7 6F6G ,6SA7,. Finally having a listen on new 6v. adaptor to my Holland made 6DJ8 Bugle Boys really nice detailed very clean sounding great separation between instruments and wide soundstage nice. Cant wait to try octals see how those sound.

 

post #4139 of 10574
Quote:
Originally Posted by MIKELAP View Post


Nice Job!
Except for the blue of course there is not quite enough shine for me... Just Kidding. tongue.gif

Now if you put two of those 3/4 to 1/2 tees end to end, you could put a 6DJ8 socket on one end and a socket for a 12AX7 on the other end ... One tube used at a time of course. Parallel wires from one B9A to the other with the appropriate changes at the socket end... biggrin.gif
post #4140 of 10574
My ceramic sockets are on the last Rickshaw out of Chi-Nee town, swinging by the USSR to grab the tubes on the way I think. biggrin.gif
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