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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 242

post #3616 of 10504
Quote:
Originally Posted by hypnos1 View Post
 

Hi all.

 

After artsi's wonderful work on the switch box, the natural-born pessimist in me is coming to the fore and pushing me to play 'devil's advocate'...

 

I may well be worrying unduly, but I am reminded of the wise statement in a related field of sound reproduction - namely : the best connector is NO connector.

Applying this principle to such a box, could we be degrading our signal transfers somewhat...especially if top grade wire isn't used, along with (possible) so-so soldering?

 

Perhaps I am barking up the wrong tree? (I know I am sometimes barking MAD!!).

 

Ah well, just a thought...

 

There certainly is some SERIOUS work going on in triode land at the moment - it's hard to keep up!

 

Keep up the good work lads - am still awaiting my sockets from China so I can see/hear what all the fuss is about...can't wait...

My concerns reading posts are about possible transformer issues if a surge would occur would like to be 100% reassured on that before making ¨THE BOX¨ . Thanks

post #3617 of 10504
Quote:
Originally Posted by gibosi View Post
 

 

Similarly, I am also wondering if my long tube rolling marathon might finally be coming to an end.... Having listened now to a number of ECC88s -- Mullard, Amperex, Siemens, Reflector and Tesla -- I find that I prefer the Amperex sound. However, even though my Amperex Bugle Boys sound incredibly good, I thought I might try to find some late 1960s Orange Globes, similar to the ones you have just ordered. Plus, I am not sure how much success I will have re-straightening the pins on my Bugle Boys, so I thought I would like to have some nice Amperex to listen to once I get my 9-pin adapter put together.

 

In my search for the OGs, I stumbled across the Amperex-USA 6922 / E88CC. Reviews I have read suggest these are among the best. And it seems to me, that if I prefer the sound of Amperex ECC88s, I might also prefer the sound of a premium Amperex over a premium Siemens or others. Plus, the price was right... :)

 

Of course, even if I am close to the end of this marathon, there are still a few other tubes I would like to try. I have read some very good reviews of Voskhod 6N23P from the 1970s. And of course, I want to try at least a few 12AX7. :)

 

Yeah, we still need to at least find out whether the 6DJ8/ECC88 or 12AX7 family are better suited for our LD amps! It's basically the reason why I just ordered a "top tier" -hopefully "god tier" lol- tube from each family.

 

Up to here, with two fairly comparable tubes from each family (both EI tubes based on the machinery that made the exact same "top tier" tubes I ordered), I am definitely preferring my 12AX7 tube! But, there is no doubt that -in the right circuits, with the right gear, blah, blah, blah- the 6DJ8 family is superior to the 12AX7 from a critical perspective. However, the LD circuits could be better suited for one type (it would almost be odd if the amp could run those two very very different tube types in the same great way, if only because of their dramatically different mu/gm figures; but the amp is pretty versatile in the first place, being able to run low mu/mid gm EF95 tubes, oddball mid mu/mid gm EF92 and high mu/high gm EF91, and of course all those crazy tubes we added to the list...).

 

Like I said, I think I might wait until I have my "top standard" tube for each family before I do anything else. My hopes are that I'll be able to immediately eliminate a tube family and save a bunch of money lol!

post #3618 of 10504
Quote:
Originally Posted by hypnos1 View Post
 

Hi all.

 

After artsi's wonderful work on the switch box, the natural-born pessimist in me is coming to the fore and pushing me to play 'devil's advocate'...

 

I may well be worrying unduly, but I am reminded of the wise statement in a related field of sound reproduction - namely : the best connector is NO connector.

Applying this principle to such a box, could we be degrading our signal transfers somewhat...especially if top grade wire isn't used, along with (possible) so-so soldering?

 

Perhaps I am barking up the wrong tree? (I know I am sometimes barking MAD!!).

 

Ah well, just a thought...

 

There certainly is some SERIOUS work going on in triode land at the moment - it's hard to keep up!

 

Keep up the good work lads - am still awaiting my sockets from China so I can see/hear what all the fuss is about...can't wait...

 

The same thing occurred to me about any effects on sound quality that the extra -poor?- wiring could have. But seeing how crappy most tube pins are (a far cry from cryo OCC copper lol!) in the first place, and how thin the wiring inside a tube is, I just can't think that it could degrade the signal that much...

 

If the inner cabling in the amp were premium, I might start worrying about it, but most of it is just PCB tracings or basic wiring anyway. I would, however, try and keep the extra wiring length at a minimum, if only out of interference concerns. These are wires that are out of the amplifier "Faraday cage", so it would be good practice to only use as much as you need (and/or shield them for experts). In the my current, semi-permanent, "mod", counting the socket savers, I only have upwards of 10cm / 4" of total extra length between the original sockets and tube pins, so nothing world-altering imo (if your soldering and connections are at least decent, obviously).

 

Quote:
Originally Posted by gibosi View Post
 

My 9-pin breadboard socket assembly arrived today.

 

And it looks pretty ugly, but it is working! lol. I found that leaving pin-9 floating still results in ground hum. But when I tied it to the catheter of the right 7-pin adapter (which is the same adapter which supplies the heaters), everything is fine. So I suspect that pin-9 just does not take kindly to being left completely disconnected. Tying it to the switch in Artsi's magic box or to the catheter in my setup makes it happy. :) 

 

Nothing is soldered. I used 28 gauge (.32mm) solid core wire and wrapped one end tightly around the test points on the 7-pin adapters, and then connected the other to the 9-pin breadboard compression terminal blocks. 

 

And of course, this is very temporary until I get around to building myself one of Artsi's magic boxes.... 

 

Testing with an RCA / Amperex (Holland) 6DJ8 from 1974. I think this was manufactured after the A-frame versions as it has a much simpler getter structure. The sound is a bit brighter than my Bugle Boys, but still very nice.... and it works! :)

 

So wait, where did you connect pin 9 finally, on one the two unused pins of the socket saver that provides the heater current? Like, pin 7 of that socket (that isn't connected to anything, right)?

post #3619 of 10504
Quote:
Originally Posted by Audiofanboy View Post
 

So wait, where did you connect pin 9 finally, on one the two unused pins of the socket saver that provides the heater current? Like, pin 7 of that socket (that isn't connected to anything, right)?

 

I remember reading that pin-9 should be tied to ground, or to one of the catheters. Since I do not yet have a suitable chassis ground connection, I tied pin-9 to pin-8 which is connected to the catheter in the right socket. And on the chance it might be relevant. I thought I should point out that I am using the right socket to supply heater current. I haven't tried the other catheter. I am still so thrilled that it is working that I don't want to change anything! lol

post #3620 of 10504
Quote:
Originally Posted by gibosi View Post
 

 

I remember reading that pin-9 should be tied to ground, or to one of the catheters. Since I do not yet have a suitable chassis ground connection, I tied pin-9 to pin-8 which is connected to the catheter in the right socket. And on the chance it might be relevant. I thought I should point out that I am using the right socket to supply heater current. I haven't tried the other catheter. I am still so thrilled that it is working that I don't want to change anything! lol

 

Ooh, connected to the one of the cathodes, I see, that makes sense; it's like shielding in a cable -connected to the source side and left "floating" at the other end. I just couldn't understand what you meant by catheter, I kept thinking about some medical looking tubing lol...

 

Hopefully, having the shield connected to only one of the two cathodes shouldn't have an audible effect, as it would be outside of the triode assembly (i.e., not between the triode elements).

post #3621 of 10504
Quote:
Originally Posted by Audiofanboy View Post
 

 

Ooh, connected to the one of the cathodes, I see, that makes sense; it's like shielding in a cable -connected to the source side and left "floating" at the other end. I just couldn't understand what you meant by catheter, I kept thinking about some medical looking tubing lol...

 

Hopefully, having the shield connected to only one of the two cathodes shouldn't have an audible effect, as it would be outside of the triode assembly (i.e., not between the triode elements).

 

Catheters... Cathodes... What was I thinking?  lol 

 

And if there is an audible effect, I certainly can't hear it. I have been listening for the past hour and so and it sounds great. :)


Edited by gibosi - 10/21/13 at 2:56pm
post #3622 of 10504
Quote:
Originally Posted by MIKELAP View Post
 

My concerns reading posts are about possible transformer issues if a surge would occur would like to be 100% reassured on that before making ¨THE BOX¨ . Thanks

 

If the possibility of having the switch in the wrong position is a concern to you, then I would suggest building two boxes with no switch: one for 6DJ8 and one for 12AX7. They are cheap to build, and having one for each tube family completely eliminates the possibility of selecting the wrong heater current.


Edited by gibosi - 10/21/13 at 3:16pm
post #3623 of 10504
Quote:
Originally Posted by gibosi View Post
 

 

If the possibility of having the switch in the wrong position is a concern to you, then I would suggest building two boxes with no switch: one for 6DJ8 and one for 12AX7. They are cheap to build, and having one for each tube family completely eliminates the possibility of selecting the wrong heater current.

So if on 6 volt position you can use 6dj8 tubes whithout having to cut pins is that right .

post #3624 of 10504
Quote:
Originally Posted by MIKELAP View Post
 

So if on 6 volt position you can use 6dj8 tubes whithout having to cut pins is that right .

 

This is true. You do not have to cut any pins. The two 7-pin adapters I am using have not been altered in any way. In each adapter, I am using pins 1 (grid), 2 (cathode) and 5 (plate) to connect the tube's two triodes to the Little Dot. And on the right adapter, I am also using pins 3 and 4 to supply heater current to the tube. And then on the tube itself, I am connecting pins 8 and 9 to eliminate ground hum.

 

So your 6DJ8 adapter would do exactly what I am doing here. And while it looks like a complicated mess, it is in fact pretty simple. :)

 

 


Edited by gibosi - 10/21/13 at 4:55pm
post #3625 of 10504

I am going to play "Devils Advocate" as well...

 

All this dual triode stuff is really great, BUT caution needs to be used in the selection of the tubes used. Rolling most of the 7 pin tubes were no problem, but with the 9 pin tubes you can be exceeding the design specs of the amplifier's transformer. Which is my main concern as I don't want to see any ones amplifier stop working.

 

 

The transformer label from my MK IV shows that the driver filament maximum current is 1Amp, this would be split between the two sides.

This transformer is a custom made one either for or by Little Dot themselves. With China being notorious for bad labeling, out of spec / poor tolerances and minimal quality control, the 0.5A rating could be anywhere from 0.4A to 0.6A all depending on who was running the toroid winding machine that day. The LD's are designed to use tubes that draw less that 0.3A and most of the tubes suggested in the manuals to roll are in the 0.175A or 0.2A range which is well below the 0.5A theoretical winding output.

 

Some of the dual triodes are very close to or are exceeding the maximum current for the winding depending on the tolerances of the transformer. The 6V duals such as E288CC / 8223 draws a filament current of 0.47A and the ECC85 / 6AQ8 / B719 & 6L12 draws 0.44A. If all was good and transformer tolerances were tight, even then these two are pushing the edge of the maximum current. Which will cause the winding to heat up and open one day leaving you with a cold tube and no filament power.

 

I doubt LD will sell you a replacement transformer, they might... If they don't, you would have to spec one out through one of the transformer manufacturers online. Which might in turn have to be a custom One Off build and that would not be cheap. There are probably lots of ready made ones on the shelf but they will not have the right dimensions to fit in the housing or they will have extra windings etc...

 

I still have an issue concerning this 6V/12V switch as there are 12V dual's that can draw current on the edge of maximum as well such as the 12AD7 drawing 0.45A.

Someone should really measure the current on a 12V tube to make sure it is not running too high.


Any Multimeter should do, just put it on the AC amps function and insert it between the center tap of the tube filament and the pin that usually connects there.

 

 

I am really not here trying to discourage anyone from playing with the dual triodes, and I am not here to spread the doom and gloom, it's just people should be aware of what the consequences might be if they decide to join in on the fun. It is good to see that the bridged filaments were discontinued as that had me concerned, since there are people trying the duals that have very little electronic knowledge.

 

In my opinion I would stick to the 6V / 0.35A or less tubes to minimize the chance of possible transformer failure and forget about implementing the switch unless you know for a fact what the current draw is and you understand how to wire such a switch...

:beerchug: 


Edited by TrollDragon - 10/21/13 at 8:30pm
post #3626 of 10504
It seems that ground hum problem concern at least tubes 6DJ8 and 6922. After workday i'm going to figure how to connect pin9 to get rid of this music spoiling noise. Cathode to free pin of my 9pin switch could solve this.

ECC83 or 6N2P-EV does not have any hum. Did not tried at all 6922 electro harmonix with new box before reading 6DJ8 hum from here.

"Grounding" pin9 in 6.3v mode makes impossible to use couple 6.3v heated tubes that have pin9 connected to filament middle. They burn to death i think.
post #3627 of 10504
Quote:
Originally Posted by TrollDragon View Post
 

I am going to play "Devils Advocate" as well...

 

All this dual triode stuff is really great, BUT caution needs to be used in the selection of the tubes used. Rolling most of the 7 pin tubes were no problem, but with the 9 pin tubes you can be exceeding the design specs of the amplifier's transformer. Which is my main concern as I don't want to see any ones amplifier stop working.

 

I am really not here trying to discourage anyone from playing with the dual triodes, and I am not here to spread the doom and gloom, it's just people should be aware of what the consequences might be if they decide to join in on the fun. It is good to see that the bridged filaments were discontinued as that had me concerned, since there are people trying the duals that have very little electronic knowledge.

 

In my opinion I would stick to the 6V / 0.35A or less tubes to minimize the chance of possible transformer failure and forget about implementing the switch unless you know for a fact what the current draw is and you understand how to wire such a switch...

:beerchug: 

 

This is very good advice, and thanks for bringing this to our attention. 

 

Fortunately, the 6DJ8 / ECC88 is .365 amps and the 12AX7 / ECC83 is .3amps (in 6 volt operation) , and these are the only double triodes I have considered rolling. But as you note, the universe of double triodes is quite large, and we should be careful to check the amperage of any new tube before we play.

 

Cheers

post #3628 of 10504

Hi Gibosi,

 

I like your idea of using connections that do not need to be soldered to try things out. From the pictures I gather that you are using one 6DJ8 tube for both channels, whereas in the past I always saw two tubes being used.

 

I have one each of the 6BS8 and 6BQ7 tubes. Can these tubes be used singly without cutting any pins (the same as the 6DJ8)?

 

I found it difficult to put together the Vector adapter after I took it apart. I assume that you took it apart to wire the adapter. What kind of crimp on pins could I use on the Vector adapter to avoid disassembling it?

 

Hi Trolldragon,

 

Would the above mentioned 6V 6BS8 and 6BQ7 tubes with a rating of 0.40 A be safe to use with the Little Dot MKIII?


Edited by mordy - 10/21/13 at 9:07pm
post #3629 of 10504
People here have been using two 7pin 0.45A tubes with no problems. This means 0.9A current from transformer in my calculations. So i think that if we stay under 0.5A with one tube everything is safe.

I have wrote currents to all "compatible" tubes in the list.

I do not suggest to anyone try crazy experiments with 6N6P etc powertubes as driver.
post #3630 of 10504
Quote:
Originally Posted by mordy View Post

Would the above mentioned 6V 6BZ7 and 6BQ7 tubes with a rating of 0.40 A be safe to use with the Little Dot MKIII?

Hey mordy!

 

Most if not all of the 0.4A tubes should be fine to use, but I personally would try to get tubes with a lower current requirement. The closer you get to that 0.5A maximum the greater the chance there is for failure and there is really no way to know what the maximum value is on the transformer other than what is printed on the label.

 

I would look into the 6DJ8 / ECC88 or the 12AX7 / ECC83 running in 6V mode like gibosi uses.

 

As I stated earlier all the "Recommended" tubes in the manuals are 0.3A's or less and this dual triode modding is really stepping outside of the design parameters of the amp.

 

So there is no way to really know if a tube is "Safe" or not, even some of the 7 pin tubes we roll are pushing the limit. The 6Ж5П's that I have in right now, have a heater current of 0.45A with a ± 0.025A tolerance, this means the tube might draw 0.425A which would be quite high, or it is drawing 0.475A which is just asking for trouble. My favorite tube the 6AH6WA can draw anywhere from 0.42A to 0.48A and I really should not be using either of these tubes.

 

Now I have to find a tube that sound as great as these two do but with less current draw, something like a 6CS6 with more bass, that would be really nice...

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