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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 312

post #4666 of 10502
Hey superdux!

1. Smoke would roll from your headphones, the amp or both... Test with cheap headphones.

2. I don't understand the question.
post #4667 of 10502

hi Trolldragon,

 

with surge i meant an overflow of electric energy in the amps circuitry. Mikelap said it had something to do with the milliamps a tube needs to run and that must be under 400ma in the LDMKIII if i remember correctly.(especially using octals with an adapter)

So using my planar headphones (T50RP), which need considerably more energy to be driven would a risk of a surge overpowering the amp be more there?

 

Sorry i´m not that good in english as i speak german most the time.


Edited by superdux - 1/15/14 at 8:04pm
post #4668 of 10502
Guten Abend Herr superdux!

The surge would not be from any amount of current draw that a headphone would place on the amplifier.

The power transformer in the Little Dot is limited to 500 ma per side on the driver tubes as far as we can tell. There is no documentation on this transformer as it is a custom one made for Little Dot. The gauge of the driver filament wires and the label on the transformer reads basically 1A / 2, so we agreed that the maximum of 500 ma per tube would be the rating.

Like MIKELAP has said to you if you keep your dual triodes (9 pin or octal) to a max of 400 ma you should have no problems.

If you want to run higher current tubes like the 6SN7 then you should set up an external filament power source like the other members here use.
beerchug.gif
post #4669 of 10502

Thx Trolldragon,

 

i get the point.Thank you for your advice

post #4670 of 10502

Sorry to bother you serious little dot tube rollers with my posting.

 

C3g tubes could be the best of the best for single triode powertube driving. 6A6 tubes are also very good sounding drivers. Curve tracer lines look very good for 6A6. http://vinylsavor.blogspot.fi/2013/02/tube-of-month-6a6.html It should be possible to drive both channels with 6A6. Only one cathode connection, so there is very tiny channel separation leakage. Heater is 0.8A! With my pan-amp i use 6A6 this way and it is impossible to hear channel leakage in normal listening.

 

I have been planning hardly my next DIY amp. Twice i nearly have ordered parts and at the last moment cancelled order. I want to use 6X5 as full wave rectifier. 6N6P's could be good powertubes. But should i use one octal socket for driver, and then i could roll nearly all my octals and with adapters 9-pin miniatyres. Or should i use two miniatyre double triodes to drive and forget mostly tube rolling with that amp. I can't decide... Somehow i think that amp sounds better with 2 triodes driving one channel.

 

Got more 6N8S tubes from 50's. Got one from 55' and it seems that there is some differences in structure if comparing to newer versions.

Getter is different in 50's to 65' with square getter. And this 55' does not have flat plates like all others and there is additional tin plates from lower mica.

 

This headphone tube amp thing is really going to get out of hand. If i don't buy more tubes, then i build more amps...

post #4671 of 10502

Audiofanboy.

 

 Yep, you certainly were right to throw C3gs into the mix, after gibosi's related findings. My heartfelt thanks go to you both; Yamamoto, and JAC Music for pushing me in that direction. Even straight out of the box they were amazing, and now with a good few hours on them I still cannot believe what they have done for this modest not-so-little amp (ie the MKIV SE).

While I am giving thanks, I for one would also like to say grazie to the founder of this thread - Dept of Alchemy - and Acapella 11, who contributed so much to this thread and is sorely missed (where are you now?!). I would have loved to hear their views on what has been achieved these past months. Thanks also to all the other regulars, who have made this thread such an education AND joy (not to mention the "tube-roller widow" indoors!!)...

 

Mordy, and anyone else interested, here is the pin layout for said C3g :

 

                     C3g               6AK5(et al)

                    

                     Pin                Pin

 

                    1&8 - H         3&4 - H

                       2  - G3(s)    

                       3  - P            5   - P

                       4  - G2(s)     6   - G2(s)

                       5  - K            2   - K,G3(s)

                       6  - G1(s)     1   - G1

                       7  - K            7  - K,G3(s)

 

As advised by gibosi, I linked C3g pins 2 & 7, to eliminate a floating grid.

 

Having connected all corresponding pins, everything is working perfectly (so far!) and trust there shouldn't be any nasty surprises further down the road...

 

Cheers everyone, and happy rolling...


Edited by hypnos1 - 1/16/14 at 1:13pm
post #4672 of 10502

Hi Gibosi,

 

Finally got my voltage regulator after waiting exactly a full month. I am using your post on page 295 as a guide, but my amp is silent - cannot coax any sound out of it.

 

My wiring is according to the diagram on p 253 for 12AX7 tubes. With this I have an octal adapter, and everything was fine and worked beautifully.

 

On your thread on p 295 you say to disconnect the wires currently connecting Vector pins 3 and 4 to the 9 pin socket pins 4 and 5, and then tape them up for future use.

 

Now, according to the schematic, 9 pin socket wires 4 and 5 for the heater are both connected to 3 on the right LD socket. Disconnecting these two wires from 3 on the Vector,  and connecting the external voltage source, results in silence.

 

What should I do with Vector wire 4 that goes to pin 9 on the 9 pin socket?

 

Could it be that the schematic you presented is for 6DJ8 tubes? What do I have to do to enable the 12AX7 setup plus the octal adapter that it should work with an external voltage source?

 

I have six 6SN7 tubes waiting to sing, and wish I could listen to them. Can anybody explain how to wire the external voltage source for the wiring of a 12AX7 with octal socket?


Edited by mordy - 1/16/14 at 4:18pm
post #4673 of 10502

Just passing this along, if anyone may be looking for a pair of Voskhod 6ZH1P-EV or Tung-Sol EF95 I'm selling some extras that I don't need...

 

http://www.head-fi.org/t/700730/fs-voskhod-6zh1p-ev-rockets-and-tung-sol-ef95-for-little-dot-darkvoice-6ak5-5654w-ef95

 

 

post #4674 of 10502
Quote:
Originally Posted by mordy View Post
 

Hi Gibosi,

 

My wiring is according to the diagram on p 253 for 12AX7 tubes. With this I have an octal adapter, and everything was fine and worked beautifully.

 

On your thread on p 295 you say to disconnect the wires currently connecting Vector pins 3 and 4 to the 9 pin socket pins 4 and 5, and then tape them up for future use.

 

Now, according to the schematic, 9 pin socket wires 4 and 5 for the heater are both connected to 3 on the right LD socket. Disconnecting these two wires from 3 on the Vector,  and connecting the external voltage source, results in silence.

 

What should I do with Vector wire 4 that goes to pin 9 on the 9 pin socket?

 

Could it be that the schematic you presented is for 6DJ8 tubes? What do I have to do to enable the 12AX7 setup plus the octal adapter that it should work with an external voltage source?

 

I have six 6SN7 tubes waiting to sing, and wish I could listen to them. Can anybody explain how to wire the external voltage source for the wiring of a 12AX7 with octal socket?

 

Since your adapter is 6SN7 on top and 12AX7 on the bottom, then you simply need to swap the vector wires with the voltage regulator wires. Pins 4 and 5 on your socket remain bridged and then connect one of the voltage regulator wires to either pin 4 or pin 5. Next, connect the other voltage regulator wire to pin 9 on the socket. Thus your 9-pin socket is configured in the 6-volt 12AX7 configuration, and all you have done is to replace the vector heater connections with voltage regulator connections.

post #4675 of 10502

Hi Gibosi,

 

Many thanks for the wiring instructions. It took a little trial and error, but I am finally listening to a 6SN7GTB 1957 Tung Sol tube now. Too early for listening impressions (or too late; it's after1.00 AM LOL).

 

Here is a picture of work in progress. Colorful spiderweb, conflicting measurements, left over old laptop power supply (?), scrap pieces of wood and foam. Pretty? No, but it works!

 

This is real! Thanks again for the help!

 

 

post #4676 of 10502

Mordy,

 

Glad to see that you have arrived in 6SN7 land! :)

 

And to all of those who have mated their LD with an external heater PS, another 600ma tube that might be worth trying is the ECC40. However, it is an 8-pin miniature and thus will require an adapter -- ECC40 to 61N/6DJ8 or ECC40 to 12A-7.

post #4677 of 10502

Hi Gibosi,

 

So far all is well. Tried four 6SN7 tubes so far; a Tung Sol '57 tall bottle, Tung Sol short bottle from '54, Raytheon US Navy unknown year, and a Sylvania '52 chrome top. All of them sound very good with the exception of the Raytheon, which sounds old and tired and restricted in the treble and bass.  The Sylvania has a great amount of detail.  However, need more time to come to a clearer impression of each tube.

 

I have a bunch of 6CG7/6FQ6 tubes that I first tried as power tubes but decided that they are not suitable for that.

 

Plugged in one 6CG7 in the the 12AX7 setup but only silence. I have a second setup for 6DJ8 tubes. Could I use this setup for the 6CG7 tubes? How should I hook up the wires?

 

Sorry for bothering you again, but I am not good at figuring out these things.

 

Thanks again for all your help.

post #4678 of 10502
To use the 6CG7, it is plug and play in a 6DJ8 socket (with your external PS).
post #4679 of 10502

Hi G,

 

To the rescue again - works fine. Using Raytheon Japan 6CG7/6FQ7 tube to begin with. Thanks again!

post #4680 of 10502
Quote:
Originally Posted by mordy View Post
 

Hi G,

 

To the rescue again - works fine. Using Raytheon Japan 6CG7/6FQ7 tube to begin with. Thanks again!


I just received my US Raytheon, and I'm loving it so far!

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