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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 109

post #1621 of 7199

I have had a little time to listen to the Siemens EK90 and the Amperex E91H using the 1-7 strapping. I don't quite know how to say this, but it is as if the warmth of the Amperex turns a bit too sweet after strapping. In my mind, these are much better unstrapped. On the other hand, the Siemens strapped sound incredibly good, I encourage those of you who were lucky enough to get these Siemens to "strap them in" and give them a try. :) 

 

I hope to get to the Telefunken EK90 later. And just to be thorough, I also plan to try the GE JG 5760/6BE6W and RCA 5915/6BY6 as well.

post #1622 of 7199

I like to first summarize the functional principle of what which strap does to heptodes. By doing this, I repeat Audiofanboy and myself but I found it useful to put recent findings into a bigger picture.

 

Let’s remind ourselves on how the LD strips 6AK5 pentodes to triodes:

 

Anode = LD PCB wires pin 5 (anode) to pin 6 (grid 2); in EF91/92 operation, jumper connects pin 7 (grid 3) to anode and grid 2. Effectively, pins 5, 6 and 7 are connected.

Grid = Pin 1 (grid 3)

Cathode = Pin 2 (cathode), 6AK5 tubes wire internally pin 7 (grid 3) to pin 2.

 

For heptodes, this allows four modes of operation to utilize pin 7 (q3, mixer grid), without heavy mod operations:

 

  1. Grid Strap” (1/7 strap), Audiofanboy’s suggestion to connect pin 7 (q3, mixer grid) to pin 1 (regular LD grid, q1). This results in a double grid, which is neither cathode nor anode strapped. Sounds great.
  2. Floating grid. Mixer grid, pin 7 is not connected, which would in the original mode of operation be used to add the oscillator frequency to the radio frequency. Works fine and yields great sound.
  3. Anode strap in EF91/92 setting, found to yield sub optimal sound performance.
  4. Cathode strap (2/7 strap), found to give poor sound performance.

 

It would be nice to find a general consensus on the strapology of heptodes but we might end up just saying tube A is the best with this setting and B is close with its preferred strap.

 

Comparison

 

Initial remarks: I haven't made this easy for myself but obviously the transferability to other tubes may not be given.All observations were done using the Siemens EK90 (6BE6) in EF95 setting.

 

1/7 strap: better definition / resolution, more forward, harder, drier, faster, bass is deeper, better articulation, more treble presence, more bass punch, better instrument separation, higher gain. Width of stage is not negatively affected.

Float: slightly more diffuse, softer, wetter, airier, more ambience, more instrument body, sweeter, more bass presence, bass goes a bit deeper, “tubier”. The plus of ambience makes the stage feel deeper and the room itself more present.

 

1/7-Triode touch: Yes, it is there. Transparency, definition of imaging, drier character / lesser perception of ambience.

 

1/7-Gain: I find the tube also slightly louder with the 1/7 strap compared to float setting. For the operation with an external oscillator, Brimmar suggests that highest gain would be achieved with a voltage of – 2 V on the oscillator.

 

Overall, the Siemens EK90 was already revealing with the float setting, which is like an easy-to-listen-to setting giving lots of ambience. After strapping it becomes an analytical audio instrument with the only disadvantage that it reduces the ambience perception, which - in full reproduction mode - is quite nice on my Senns. Either 1/7-strap or no strap, the tube sounds great. At the moment, if I had to choose, my favour would go to the 1/7-strap because of its definition / resolution but I would have to do a few even longer listening sessions for ultimate conclusion. This would be my best sounding setup overall.

 

1/7-strap comparison between tubes

 

Siemens EK90 (6BE6) sounds more transparent, airier, more treble presence (“triode touch”), bass most differentiated, Tung Sol 6BE6 gentler with more ambience, more relative bass presence, more tube like, between Siemens and Sylvania. Sylvania JAN 5750, most relative bass presence, sounds darkest.

 

In order to compare cross family differences, I sought to find a Siemens 6BY6 (EH900, EH900S, EH960, E91H), but couldn't find one. In contrast, the 6CS6 (EH90) are easily available, which aren't yet in my collection. I bought a pair of those.

 

Gibosi, excellent work reviewing the heptodes on page 105. I was starting to go through my heptodes as mentioned above but I have to come back later to draw more detailed conclusions between tubes. Funny, I just came up with this post after you strapped your Siemens EK90.

 

Mordy, I think you would probably favour a 1/7-strapped heptode, because it yields more treble presence, sounds more forward. I am guessing you just need the right manufacturer to suit your sweet tooth.

 

Audiofanboy, The depth of stage / ambience effect is IMO probably differently highlighted depending on headphones, especially considering that the HE-500 is known to not have a very deep stage and the HD800 produces one of the largest volumes of stage spaces. I might use the HE-500 for comparison as well at one point. As for your larger quantity of the positive treble energy, this is probably what I have described as  treble presence and it looks like we agree on this one.

 

Update: Added EF95 setting info.


Edited by Acapella11 - 6/23/13 at 2:28pm
post #1623 of 7199

A11,

 

Thanks for your in depth post. Just to make it clear to myself, are all the various figurations using the E95 setting?
 

post #1624 of 7199
Quote:
Originally Posted by mordy View Post

A11,

 

Thanks for your in depth post. Just to make it clear to myself, are all the various figurations using the E95 setting?
 


Yes

post #1625 of 7199
Quote:
Originally Posted by Acapella11 View Post


Yes


Well, good lord, that's some great work A11! More synthetic and easy on the eyes than when I write my own conclusions lol...!

 

But, yes, the strapping setting does, on my setup, give a unique, and profoundly engaging sound, unlike anything I heard in those past months of rolling. The treble presence/detail/energy, and the way the stage and instruments are rendered is quite an out of this world experience; seriously.

 

The one thing I think we need to find a consensus of sorts on -or basically a pattern- is whether this pin 7-1 mod yields the same results for all three identified types of heptodes. There are inherent differences in the way 6BE6, 6BY6 and 6CS6 tubes are built and function -regardless of their intended application though it would be linked- especially on the cutoff characteristics of grid 3, so we should expect to find some degree of difference. For 6BE6 tubes, I read somewhere (too tired to find and post the quote, but I'll edit afterwards) that grid 3 exhibits remote-cutoff curves, whereas the -yet untested, how is that even possible btw?- 6CS6's grid 3 is your typical sharp-cutoff; haven't found how grid 3 behaves for 6BY6 yet.

 

All I can say for now, before I get my next premium 6BY6 types, is that my strapped 5915 give me the greatest listening pleasure and staging (large, deep, wide, and realistic) I've heard on my HE-500; and I'm pretty sure that the treble presence/detail/energy would complement many people's Senn HD650 phones very well too.

 

Nice work though chaps, this here, what we've just found out, is a clear and obvious breakthrough, the likes of which I don't believe we'd had since testing the 6AU6 and 6AH6 families -that and some triodes as a side job lol!

post #1626 of 7199

Hi all, and especially thanks for your encouragement,

 

Looks like I did something wrong the first time I set up the 1-7 strap with the heptodes. In general I have always been in consonance with every-body's findings on these wonderful new tubes, and it bothered me that I could not hear what others were describing.

 

Now I tried again, and the sound is just great!

 

 

"Mordy, I think you would probably favour a 1/7-strapped heptode, because it yields more treble presence, sounds more forward. I am guessing you just need the right manufacturer to suit your sweet tooth."

 

"The treble presence/detail/energy"

 

Yes i do like sweets, and this is real ear candy. My RCA 6BY6 tubes now sound exactly like you described with plenty of volume. There is a lot of energy and detail in the highs.

 

Very happy that I can enjoy the heptodes now!

 

 

After spending some time with these I will report again.

post #1627 of 7199

I am listening to some TUNG-SOL 6BE6 with 7-1 strapping on EF-95 setting very nice sounding with the senns   and my go to tune DUKE ROBILLARD ALBIE AINT HERE  xylophone  is crisp bass to die for  i think i gonna  cry jjjjjjust kitting anyway another great tube will check them again without strapping to see the difference could these be the best tubes ive heard im not worth c.....p at describing but i now a good tube when i hear one ..Good nite and have a pleasent tomorrow.

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post #1628 of 7199

Mikelap... Mordy... Glad to see that heptode land is agreeing with you! :)

 

This evening I quickly checked out the Telefunken EK90, GE JG 5760/6BE6W and RCA 5915/6BY6. Mind you, this was listening to each tube for about 2 minutes. I just wanted to see if it would be worth my while to spend more time with any of them.

 

The Results: The TFK and the RCA easily passed the test, but the GE couldn't hold my interest for even 2 minutes! lol  Oh, and I just remembered that I have a pair of Brimar CV4012.... I need to test them too.....

post #1629 of 7199

OK, I found the information I was missing last night, on the cutoff characteristics of grid 3 on those heptodes; and I found it from a more official source than forums this time: the datasheets -which I'd had for weeks...

 

So:

 

- 6BE6: grid 1 = sharp cutoff, grid 3 = remote cutoff (cutoff in triode mode when tied together ? )

- 6BY6: grid 1 = sharp cutoff, grid 3 = sharp cutoff (so we'd expect a sharp cutoff trait when triode strapped, probably...)

- 6CS6: grid 1 = sharp cutoff, grid 3 = sharp cutoff (so same as above...?)

 

Just food for thoughts...

post #1630 of 7199

Is there any good power tubes to replace stock for the LD MKIII without breaking bank? electro harmonix 6h30pi is a bit expensive.

post #1631 of 7199
Quote:
Originally Posted by Audiofanboy View Post

OK, I found the information I was missing last night, on the cutoff characteristics of grid 3 on those heptodes; and I found it from a more official source than forums this time: the datasheets -which I'd had for weeks...

 

So:

 

- 6BE6: grid 1 = sharp cutoff, grid 3 = remote cutoff (cutoff in triode mode when tied together ? )

- 6BY6: grid 1 = sharp cutoff, grid 3 = sharp cutoff (so we'd expect a sharp cutoff trait when triode strapped, probably...)

- 6CS6: grid 1 = sharp cutoff, grid 3 = sharp cutoff (so same as above...?)

 

Just food for thoughts...

 

I'm currently testing the EH900S with the 2-7 strap and I'm finding that they have a very detailed presentation with a decent soundstange compared to my previous EF95 configuration with a blasé experience.

 

Drums are also very punchy and quick, even on the HD650. Some harder Buckethead stuff really shines with this configuration.

 


Edited by mab1376 - 6/24/13 at 5:38am
post #1632 of 7199
Quote:
Originally Posted by mab1376 View Post

 

I'm currently testing the EH900S with the 2-7 strap and I'm finding that they have a very detailed presentation with a decent soundstange compared to my previous EF95 configuration with a blasé experience.

 

Drums are also very punchy and quick, even on the HD650. Some harder Buckethead stuff really shines with this configuration.

 

 

 

Trumpets and drums are amazing on this track with the above configuration.

 

Piano sounds like its in the room with you. very impressed so far!

 

Mids have a VERY forward feeling like the guitar in in my face.

 

And I still want a pair of those Siemens EK90! Can't find it anywhere!

 

-edit-

 

don't know how I double posted, whoops.


Edited by mab1376 - 6/24/13 at 7:52am
post #1633 of 7199

Dear Mab 1376,

 

Here is a link to German EBay for Siemens EK90 tubes (three offerings, but don't know about pairs - you have to ask seller):

 

http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=Siemens+EK90&LH_PrefLoc=2

 

To find these tubes when you go to EBay, look on the left  and scroll down to the heading Location; then click on Worldwide.

 

Hope this is of help
 

post #1634 of 7199
Quote:
Originally Posted by mordy View Post

Dear Mab 1376,

 

Here is a link to German EBay for Siemens EK90 tubes (three offerings, but don't know about pairs - you have to ask seller):

 

http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=Siemens+EK90&LH_PrefLoc=2

 

To find these tubes when you go to EBay, look on the left  and scroll down to the heading Location; then click on Worldwide.

 

Hope this is of help
 

 

Looks like they all only have one each.

 

I usually try a buy in pairs with similar date codes, I've had some issues in the past where there was a noticeable difference between channels.

post #1635 of 7199
Quote:
Originally Posted by siles1991 View Post

Is there any good power tubes to replace stock for the LD MKIII without breaking bank? electro harmonix 6h30pi is a bit expensive.

 

My suggestion is 6N6P-IR. For me, the best solution before and way cheaper than the 6H30P-DR. Don't be fooled by the 500 h guaranteed time of operation. This is under impulse mode, which we don't use with the LD. Since it is made for even worse conditions than normal power tubes, I am guessing that it lasts at least as long as any other regular 6N6P tube. The R means a special low noise quality, which also is a special feature indicating a tube of highest quality. As for years of production, try to buy pre-1984 power tubes, as this indicates tubes of the old Russian quality.

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