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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 105

post #1561 of 6944

Those Telefunken tubes do look great, I ought to try some at some point. ;)

 

To continue on my technical ramblings -that nobody seems to care about anyway lol- I've found a bit more information that confirms that my reasoning about heptodes isn't totally out there, and that at least a few of my ideas not only work, but have been used in various schematics.

 

From some random forum post found on google:

 

"I understand what you are saying, and in fact in researching the ways a heptode can be used, I found several example where it is connected as a triode and one where it is connected as a pentode.
All in all, since g5 is tied to the cathode internally, and g2 and g4 are also tied together internally, we have the following combinations:
As pentode G2 + G4 used as screen grid and:
1. G1 tied to cathode, G3 used as the control grid (*)
2. G3 tied to cathode, G1 used as the control grid
3. G1 + G3 tied together used as control grid
4. G3 tied to plate, G1 used as control grid
5. G3 tied to G2+G4, G1 used as control grid

As triode:
1. G2+G4 and G3 tied to plate, G1 is the control grid
2. G2+G4 tied to plate, G1 tied to cathode, G3 is the control grid (*)
3. G2+G4 tied to plate, G3 tied to G1 and used as control grid (*)
4. G2+G4 and G3 tied together used as control grid, G1 tied to cathode
5. G2+G4 and G1 tied together used as control grid, G3 tied to cathode
6. G2+G4, G1 and G3 tied together used as control grid
7. G1 and G3 tied to cathode, G2+G4 used as control grid

That makes 5 different pentodes and 7 different triodes but not all are equally promising. The combinations marked with (*) I have seen in various schematic diagrams.
In particular, G2+G4 do seem to be the equivalent of a pentode screen grid, so probably pentodes 1-3 and triodes 1-3 are the useful ones.
"

 

So, basically -forgetting about the grounded anode idea for the time being- this guy says that two of my suggestions work.

 

- Strapping pin 6 to pin 5 (grid 2 and 4 to anode, the amp does on the EF95 setting anyway), chopping pin 1 off and somehow tying it to pin 2 (strapping grid 1 to the cathode, doable but difficult without an adapter) and wire-modding pin 7 to socket hole 1 (using grid 3 as the signal grid). EF95 setting.

 

- Or -much easier- strapping pin 6 to pin 5 (same as above, basic EF95 setting), and wire-modding pin 7 to pin 1 (tying grids 1 and 3 together).

 

Now, of these two options, number 2 is the obvious winner. Most of you are already using those heptodes/pentagrid converters with grid 3 (pin 7) floating and have reported that it works better that way. That is probably -as I wrote earlier- because grid 3 is intended, like grid 1, to be a control -signal- grid, and you don't want a signal grid without a signal tied to the anode sandwhiched between two screen grids.

 

So, instead of just leaving grid 3 floating -which despite everything else, can't be ideal- why not try and strap it with the good ol' wire-mod to pin 1 (with the same EF95 setting)? It makes perfect sense to be using the "signal" grids in a heptode for, well, signal purposes, and tying everything else to the anode.

 

Anyone feel like trying before I do it? ;)

post #1562 of 6944

Maybe i'll try this on my Tung-Sol 6BE6 and see what happens in a day or two when i get some time.

 

just strap 7-1 right?

post #1563 of 6944
European Heptode Shoot Out (EF95)
 
(I know.. I know... I should do this all over again, strapping pins 1 and 7, but I am too lazy!  Soooo sorry :)
 
Amperex 6687/E91H (6BY6), Brimar CV4012 (6BE6), Siemens EK90 (6BE6) and Telefunken EK90 (6BE6). I purchased the three 6BE6 from the NOStubestore in Turkey and the 6BY6 from an eBay vendor in the states.
 
First, as a group, none of these tubes bring background sounds too close as is the case with some triodes and a few other heptodes I have heard. Moreover, all of these tubes have the typical "heptode sound" we have come to expect, with a powerful and punchy bass, an extended, but not overly bright treble, a clean and round midrange, and a wide sound stage with excellent imaging. Also interesting, I found this collection of tubes to be a nice example of the so-called "British - Holland - German sound continuum" that goes from warm and comfortable to detailed and airy.
 

 

First is the British sound, the Brimar CV4012.  As AFB has already noted, this tube has a very thick and heavy bass, and a large and deep soundstage with good instrument separation. Vocals and horns are mellow and warm, with extended, but not overly bright highs. Even though the bass is kind of mushy, I still find these tubes to be very enjoyable and easy to listen to.
 

 

Next is the Holland sound, the Amperex 6687/E91H. The bass is cleaner and more articulate than the Brimar bass, but still very powerful and punchy. Vocals, piano and horns are still rather warm, but not as warm as the Brimars, and the upper mids and highs are a bit brighter, with a good bit of air and detail. And like the Brimars, these have a very wide and deep soundstage with good instrument separation. I feel these Amperex are a very delicious blend of warmth and detail. In my mind these are "refined" Brimars.
 

 

Next is the Siemens EK90 version of the German sound. The bass is powerful, punchy and articulate, but it doesn't have quite the weight of the Amperex. Vocals, piano and horns are a bit more forward than the Amperex, airy and detailed. And of course, these have a very wide and deep soundstage with good instrument separation. The Siemens seem to me to be intermediate between the Holland/Amperex sound and the Gerrman/Telefunken sound, the best of both in my mind.
 

 

And finally, the Telefunken EK90 version of the German sound. The bass is very comparable to the Siemens, but again, it doesn't have quite the weight of the Amperex. Vocals, piano and horns are the most forward of all these tubes with plenty of air and detail, clean and transparent. And as with all of these tubes, the Telefunkens have a very wide and deep soundstage with good instrument separation. In my opinion these are the epitome of the German sound, detailed, airy and clean.

 
Which is the best? I don't think it is possible for me to say. What I can say is that I believe the Brimar is not quite in the same league as the others. However, I think choosing among the remaining three comes down to which one works best with your sources, your headphones and your preferred sound signature. So I will take the easy way out and recommend that everyone should have all three. :)
post #1564 of 6944
Quote:
Originally Posted by gibosi View Post

European Heptode Shoot Out (EF95)
 
(I know.. I know... I should do this all over again, strapping pins 1 and 7, but I am too lazy!  Soooo sorry :)
 
Amperex 6687/E91H (6BY6), Brimar CV4012 (6BE6), Siemens EK90 (6BE6) and Telefunken EK90 (6BE6). I purchased the three 6BE6 from the NOStubestore in Turkey and the 6BY6 from an eBay vendor in the states.
 
First, as a group, none of these tubes bring background sounds too close as is the case with some triodes and a few other heptodes I have heard. Moreover, all of these tubes have the typical "heptode sound" we have come to expect, with a powerful and punchy bass, an extended, but not overly bright treble, a clean and round midrange, and a wide sound stage with excellent imaging. Also interesting, I found this collection of tubes to be a nice example of the so-called "British - Holland - German sound continuum" that goes from warm and comfortable to detailed and airy.

 

Lol, it always makes me laugh when some of my odd formulations end up sticking; this one was meant more as a metaphor, and now it's becoming an actual measuring unit!

 

Nice work though, gibosi, that's exactly the kind of push and data I needed to go ahead and (re-)try and buy heptodes. That, and what I just tested. Keep reading.

 

As I wrote a couple of hours ago, strapping grids 1 and 3 in heptodes was apparently not only possible, but made perfect sense. So, I tried it. And guess what, it works -which it should- has more gain -which makes sense- and sounds awesome -which is more interesting!

 

Basically, it seems that sending the audio signal through both grid 1 and grid 3 adds the effect of the two grids, which is what that kind of tube was made for originally: mixing signals (or something along these lines I believe).

 

I tested this on what was supposed to be my best heptode out of the ones I had bought a few weeks ago (one pair of Telefunken EH900S in Tele boxes with "Bundeswehr" German military tags and Tele logos and "eagle" on the tubes, which were actually Sylvania 5915; very solid looking though, and still rated for 10K hours as EH900S should be; and two pairs Brimar CV4012, including one which was supposed to be Mullard but wasn't; not the best tubes anyway), so the Tele/vanias 5915/EH900S.

 

- With grids 2 + 3 + 4 strapped to the anode (basic EF92 setting), they sounded like crap, seriously; all my heptodes did, hence my not using them since then. They sounded dull, flat, boomy... The Brimar were even worse

 

- With grids 2 + 4  strapped to the anode and grid 3 left floating (basic EF95 setting), they opened up and suddenly sounded like top-tier tubes. Similar in relative sound quality and balance to my best pentodes, but slightly different. Wide and open soundstage, nicely detailed and strong-ish bass -not sub-bass though- and a bit of that pleasing and euphonic low-mids emphasis that many pentodes have, just a little. Anyway, top-tier, musical, and more realistic than my best pentodes (on par with the Tung-Sol 6485).

 

- With grids 2 + 4 strapped to the anode (EF95 setting) and grid 3 strapped to grid 1 (wire mod from pin 7 to pin 1, you can't do it wrong, it's the only two pins separated by a gap!), the tubes became different beasts. Basically, they started sounding almost triode-like -never thought I'd end up using that expression to describe tubes- in a good, very good, way. Open, airy, boundless soundstage, upper-end detail like you wouldn't believe (and I've been running pure triodes for weeks, so I've gotten pretty picky about upper end detail), and clarity, so much clarity. Voices are just there, thin or thick, husky or mellow; the sound is almost un-tube like in some ways -just like some 6AV6 tubes actually- with none of that mids and low-mids hump or blurry emphasis that, while euphonic, takes away some clarity.

 

As I said earlier, there is also more gain with that new setting; I'd try it if just for that (gain goes from the equivalent of a 6AK5 to about the same as a 6AU6, so maybe mu = 36~40 instead of 20).

 

At any rate, I strongly believe you should try this if have a few heptodes lying around, or if you're actually using pentodes; and anyway, once you look at what these tubes were made for and the purpose of each grid, it makes sense. Be warned, the tubes do sound quite different between the two settings, so I'm sure some of you will end up sticking with the former.


Edited by Audiofanboy - 6/18/13 at 7:48am
post #1565 of 6944

Hi Gibosi,

 

My wife asked me last night why I need so many tubes, especially since I do not use a lot of them. After some thought, I came to the conclusion that I have the same question....

 

(I tried to explain to her that I am looking for the ultimate in sound, but could not come up with a good example that she could relate to. My wife is the kind of person who recognizes her car based on the color, and more than once she tried to open up somebody else's car door because the car had the same color.)

 

So, here is the question to you: How do the European pentodes compare to the US made Tung Sol 6AH6WA/6485 and the Westinghouse Tektronix 6AU6/4825 tubes? These two tubes are on the top of my list currently, and I am very happy with them.

 

Would a Siemens EK90 bring more to the table?
 

post #1566 of 6944
Quote:
Originally Posted by mordy View Post

Hi Gibosi,

 

My wife asked me last night why I need so many tubes, especially since I do not use a lot of them. After some thought, I came to the conclusion that I have the same question....

 

(I tried to explain to her that I am looking for the ultimate in sound, but could not come up with a good example that she could relate to. My wife is the kind of person who recognizes her car based on the color, and more than once she tried to open up somebody else's car door because the car had the same color.)

 

So, here is the question to you: How do the European pentodes compare to the US made Tung Sol 6AH6WA/6485 and the Westinghouse Tektronix 6AU6/4825 tubes? These two tubes are on the top of my list currently, and I am very happy with them.

 

Would a Siemens EK90 bring more to the table?
 


American tubes, especially Tung-Sol tubes, have a fruitier sound than most non-UK European tubes. More oomph and subjective power in the low-mids region among other things, and sometimes slightly rolled-off treble and thicker, rounder bass. GE tubes would also tend to be like this, pretty balanced and mellow but not very airy; Sylvania tubes would be more detailed and airy, and in some ways closer to European non-UK tubes. I haven't owned enough RCA or Raytheon tubes to compare.

 

I'd still try a heptode or two, if only for the thrill of it. Maybe just wait another couple of weeks for the top-three list to be firmly established, depending on which setting is used.

post #1567 of 6944
Quote:
Originally Posted by mordy View Post

So, here is the question to you: How do the European pentodes compare to the US made Tung Sol 6AH6WA/6485 and the Westinghouse Tektronix 6AU6/4825 tubes? These two tubes are on the top of my list currently, and I am very happy with them.

 

Would a Siemens EK90 bring more to the table?
 

 

To follow up on Audiofanboy's comments, I find the Siemens EK90 to be just as good as the TS 6485 and the W 4825, but slightly different, in that the Siemens EK90 seems to have a bit more air and detail. The 6485, 4825 and EK90 are all exceptional tubes and I enjoy all of them. But again, as those of us who have these heptodes will now feel compelled to go back and try them again with pins 1 and 7 strapped, it might be best to watch from the sidelines until the dust finally settles. :)

post #1568 of 6944
Quote:
Originally Posted by mab1376 View Post

I am absolutely in love with my Telefunken 6BE6 using with standard EF95 settings.

I emailed NOSTUBESTORE about getting some Siemens 6BE6 to compare... but SOMEONE bought all of them recently according to the owner... confused_face(1).gif

 

I'm sure I could find a pair somewhere else, just haven't looked yet.

 

Eventually I'll try out my EH900S with gold pins.

 

Hi mab,

 

Oh dear, I sincerely hope all my ravings about the Siemens EK90 haven't encouraged someone to do a spot of profiteering...I am glad however that they are proving to be a popular choice...

And deservedly so, methinks.

 

After Genesis/ELO type rock(?), am now seeing what they can do with classical..and WOW - my head is bursting. Piano is awesome; kettle drums astounding; violin 'scratchy' - in the best possible sense ; flute obviously blown; harp so gorgeous I could die; brass nice and raspy (and as for the tuba!...); triangle 'tingly', etc. etc. And all in a wonderfully integrated spatial configuration - even the 'mad' cacophony of Mussorgsky's Great Gate of Kiev (Pictures at an Exhibition - orchestral version). I am now truly in sonic heaven...should I try Audiofanboy's latest finding? Am almost too afraid to do so!...But probably will...


Edited by hypnos1 - 6/18/13 at 11:51am
post #1569 of 6944
Quote:
Originally Posted by hypnos1 View Post

 

Hi mab,

 

Oh dear, I sincerely hope all my ravings about the Siemens EK90 haven't encouraged someone to do a spot of profiteering...I am glad however that they are proving to be a popular choice...

And deservedly so, methinks.

 

After Genesis/ELO type rock(?), am now seeing what they can do with classical..and WOW - my head is bursting. Piano is awesome; kettle drums astounding; violin 'scratchy' - in the best possible sense ; flute obviously blown; harp so gorgeous I could die; brass nice and raspy (and as for the tuba!...); triangle 'tingly', etc. etc. And all in a wonderfully integrated spatial configuration - even the 'mad' cacophony of Mussorgsky's Gate of Kiev (Pictures at an Exhibition - instrumental version). I am now truly in sonic heaven...should I try Audiofanboy's latest finding? Am almost too afraid to do so!...But probably will...


Do it lol! I'm dying to have new and different impressions of all these tubes with that new setting! If only just to compare with what I heard.

 

Has anyone tried the EH90 (6CS6) type, the third of the 7-pin heptode family? They seem to be easily available.

post #1570 of 6944
Quote:
Originally Posted by hypnos1 View Post

 

Hi mab,

 

Oh dear, I sincerely hope all my ravings about the Siemens EK90 haven't encouraged someone to do a spot of profiteering...I am glad however that they are proving to be a popular choice...

And deservedly so, methinks.

 

After Genesis/ELO type rock(?), am now seeing what they can do with classical..and WOW - my head is bursting. Piano is awesome; kettle drums astounding; violin 'scratchy' - in the best possible sense ; flute obviously blown; harp so gorgeous I could die; brass nice and raspy (and as for the tuba!...); triangle 'tingly', etc. etc. And all in a wonderfully integrated spatial configuration - even the 'mad' cacophony of Mussorgsky's Gate of Kiev (Pictures at an Exhibition - instrumental version). I am now truly in sonic heaven...should I try Audiofanboy's latest finding? Am almost too afraid to do so!...But probably will...

 

I've emailed about 5 different tube sites and no one has the Siemens in stock. I do have the Telefunken's though, so I don't feel left out lol.

 

I really like them with very fuzzy rock such as Kyuss and The Black Keys, even though its enjoyable it doesn't do it any justice. to really get a feel for what they're capable of run through the Muse album Resistance. I also really like the Maxence Cyrin Piano cover album with them.

 

This is also quite and enjoyable track:


Edited by mab1376 - 6/18/13 at 11:01am
post #1571 of 6944

Tried my 1966 RCA 6BY6  hep tubes with the new 1-7 strap setting. (Used the jumpers I made for the 5-6 setting which fit fine over the gap.) The treble is super detailed and the bass is strong, and the brightness gave way for mellowness. The first thing I noticed was a marked decrease in volume and I had to turn up the volume quite a bit. [If I was using the TS tubes my neighbors would complain with this volume setting.]  The sound was very detailed but lacked sweetness, and after a while I could not listen any more and had to put back the Tung Sol 6AH6WA tubes(I assume that the TS 6485 sound the same although I have not heard them).

 

Relief. Looks like I prefer the juicy (fruity?) punchy bass and crystal clear presentation. Could be that my system does not like heptodes; maybe it's me.

 

I do recognize that other people, depending on their equipment and preferences, may like the sound of the heptodes but so far, it's not for me.

post #1572 of 6944

The E91H is a special heptode with a passivated third grid designed to reduce secondary emission; this device was used as a "gate", allowing or blocking pulses applied to the first, (control) grid by changing the voltage on the third grid, in early computer circuits (similar in function to the U.S. 6AS6).

 

http://en.wikipedia.org/wiki/List_of_vacuum_tubes#Special_quality_tubes

 

E91H Normally replaceable but slightly different than the 6BY6

 

Basically G3 should always be floated to reduce crosstalk.


Edited by mab1376 - 6/18/13 at 12:31pm
post #1573 of 6944
Quote:
Originally Posted by mordy View Post

Tried my 1966 RCA 6BY6  hep tubes with the new 1-7 strap setting. (Used the jumpers I made for the 5-6 setting which fit fine over the gap.) The treble is super detailed and the bass is strong, and the brightness gave way for mellowness. The first thing I noticed was a marked decrease in volume and I had to turn up the volume quite a bit. [If I was using the TS tubes my neighbors would complain with this volume setting.] 

 

Quote:
Originally Posted by Audiofanboy View Post

As I said earlier, there is also more gain with that new setting; I'd try it if just for that (gain goes from the equivalent of a 6AK5 to about the same as a 6AU6, so maybe mu = 36~40 instead of 20).

 

 

Audiofanboy writes that there should be more gain, not less. And yet, your experience was just the opposite? This is very curious.... Later this evening, I will try out this strapping on one of my heptodes....
post #1574 of 6944
Quote:
Originally Posted by mordy View Post

Tried my 1966 RCA 6BY6  hep tubes with the new 1-7 strap setting. (Used the jumpers I made for the 5-6 setting which fit fine over the gap.) The treble is super detailed and the bass is strong, and the brightness gave way for mellowness. The first thing I noticed was a marked decrease in volume and I had to turn up the volume quite a bit. [If I was using the TS tubes my neighbors would complain with this volume setting.]  The sound was very detailed but lacked sweetness, and after a while I could not listen any more and had to put back the Tung Sol 6AH6WA tubes(I assume that the TS 6485 sound the same although I have not heard them).

 

Relief. Looks like I prefer the juicy (fruity?) punchy bass and crystal clear presentation. Could be that my system does not like heptodes; maybe it's me.

 

I do recognize that other people, depending on their equipment and preferences, may like the sound of the heptodes but so far, it's not for me.

 

Interestingly, while gain seems higher for strong signals -like music- I have noticed that it also seems less linear. Basically, if a signal isn't that strong in the first place, I'll need a lot more volume to actually get more sound, whereas a strong signal will only need about as much volume as a 6AU6 to sound loud. But then again, maybe I also needed a lot more volume on the EF95 setting alone to get more sound, I didn't test it with "weak" signals like the audio from a video; and I confirm I do need less volume for basic music playback.

 

And like I said, I immediately recognized that the sound is different from both "pentode" sound and heptodes on the EF95 setting, so I'm not surprised that it would not be your fav'.

 

Quote:
Originally Posted by mab1376 View Post

The E91H is a special heptode with a passivated third grid designed to reduce secondary emission; this device was used as a "gate", allowing or blocking pulses applied to the first, (control) grid by changing the voltage on the third grid, in early computer circuits (similar in function to the U.S. 6AS6).

 

http://en.wikipedia.org/wiki/List_of_vacuum_tubes#Special_quality_tubes

 

E91H Normally replaceable but slightly different than the 6BY6

 

Basically G3 should always be floated to reduce crosstalk.

 

From what I've read, there are two kind of heptodes (at least for the ones we use), the ones meant to "mix" or be useful for two separate signals, and the ones meant to "block or let let a signal through" where only one incoming signal is relevant. The E91H seems to be one of the latter, while most 6BE6 seem to be the former; but I still need to look into this some more.

 

Again, from a theoretical perspective, both floating or strapping grid 3 make sense, and it yields different -good- results, so I'd just try both and use the preferred one.


Edited by Audiofanboy - 6/18/13 at 12:42pm
post #1575 of 6944
Quote:
Originally Posted by mab1376 View Post

 

Do you prefer the 6BE6 on the EF92 setting as opposed to the EF95 setting?

Just noticed that they possibly sound better on EF95 (page 77).did not try them on other setting (EF95)yet will leave on EF92 for a a bit .

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