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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 221

post #3301 of 10502
Quote:
Originally Posted by MIKELAP View Post
 

Looks like theres 2 mods  one is this by AFB :

Yes, basically you are trying to use only the first triode in the tube, so all the leftover pins need to be neutralized or at least out of the way. So, pins 1, 2, 3 & 9 of the 6BQ7A need to be bent or cut, while pins 4, 5, 6, 7 & 8 can be inserted in a sequence into the socket hole 3, 4, 5, 6 & 7 of your adapter. Next, you just have to link/solder pin 6 to pin 1, and pin 7 to pin 2 on the adapter (with pins 6 & 7 disconnected at the base), and voila! You get a single 7-pin triode!

 

And on post #3145 at the bottom gibosi speaks of a wiring harness that is linked to another socket with no tube this mod using the 2 triodes of the tube instead of one if i am not mistaken in the first mod. One thing thats not clear in 2nd mod  is the ground part is that settled ? Thats what i think i know am i correct ? A complete procedure would be great in time when everything is settled and clear.

 

I tried to use both triodes in the tube, plugging the tube into the left socket and connecting the second triode - cathode, grid and plate - to the appropriate pins in a socket adapter plugged into the right socket.

 

http://www.head-fi.org/t/563884/little-dot-tube-amps-vacuum-tube-rolling-guide/3180#post_9847725

 

However, there was a very strong ground hum from the empty socket on the right. As this ground hum is totally independent of the volume, I suspect that there is some kind of grounding problem relative to the two sockets. My suspicion is that it might be a result of the fact that both cathodes, left and right, are being heated through the left socket. The only idea I have had to date is to connect pin 9, a shield grid, to a chassis ground. However, as I do not have much hope that this will actually work, I haven't gotten around to giving it a try....

post #3302 of 10502
All the heater wires come directly from the torrid transformer on top. 2 pair for the back and 2 pair for the front. I'll have to pull off the cover ans see if there is a number on it for a pinout.

If the two front windings are center tapped then you would just need the appropriate wire from each side for the 12V heater. I would look for a pinout first before you bridged and heater wires though.
post #3303 of 10502
Hey AFB!

MIKELAP sent me a picture of what is your MK IV SE's board section, there is a Linear 1084 modded in on a heat sink. Is this stock or a mod you have done? Possibly a CCS implementation? The input caps are missing as well. Do you have any full pics of the board?
beerchug.gif
Edited by TrollDragon - 10/4/13 at 7:53pm
post #3304 of 10502
Well took the 6AV6's down to my little workshop, cleaned up the pins and loaded a 1/32" rigid cutting disk into the Dremel.

Half speed spin and precisely lopped of the two pins perfectly flush with the glass base, there isn't even a little ridge that you can feel with a finger nail.

A job well done, very clean and easy till I looked closer and realised I had cut off 4 & 5... frown.gif

So I lopped off 6 and made a little pad out of solder wick to butt solder to the flush pin 4 stub, twisted two Cat5 strands very tightly and soldered that to the pad. Checked the heater pins with the meter and there is continuity.

It won't last but it will allow me to try out the NEC's to see if its worth getting a replacement tube or two from Taiwan.

Of all the bone headed maneuver's...
Edited by TrollDragon - 10/4/13 at 7:54pm
post #3305 of 10502
Quote:
Originally Posted by TrollDragon View Post

Well took the 6AV6's down to my little workshop, cleaned up the pins and loaded a 1/32" rigid cutting disk into the Dremel.

Half speed spin and precisely lopped of the two pins perfectly flush with the glass base, there isn't even a little ridge that you can feel with a finger nail.

A job well done, very clean and easy till I looked closer and realised I had cut off 4 & 5... frown.gif

So I lopped off 6 and made a little pad out of solder wick to butt solder to the flush pin 4 stub, twisted two Cat5 strands very tightly and soldered that to the pad. Checked the heater pins with the meter and there is continuity.

It won't last but it will allow me to try out the NEC's to see if its worth getting a replacement tube or two from Taiwan.

Of all the bone headed maneuver's...

Everytime before cutting  i always look at this picture i took.Better safe then sorry.and i use a cutter more control . Arrows show pins to be cutoff.


Edited by MIKELAP - 10/4/13 at 8:09pm
post #3306 of 10502
Quote:
Originally Posted by TrollDragon View Post

If the two front windings are center tapped then you would just need the appropriate wire from each side for the 12V heater. I would look for a pinout first before you bridged and heater wires though.

 

I am afraid that doing something like this is way beyond my comfort level!  And even if, since the 6DJ8 is a 6 volt tube, with only one set of heaters, pins 4 and 5, servicing both triodes, I really can't see how it would be possible to heat them separately.

 

Another idea rattling through my mind is strapping the two cathodes together, but I worry about an inadvertent fireworks display lol.

 

At this point, I figure I am in way over my head, and have resigned myself to continue listening to mangled pairs of 6DJ8 for the time being. But of course, I am hoping someone with more experience and expertise might be able to figure out a way to use both triodes in one tube.

post #3307 of 10502
Quote:
Originally Posted by MIKELAP View Post

Everytime before cutting  i always look at this picture i took.Better safe then sorry.and i use a cutter more control . Arrows show pins to be cutoff.

Thanks MIKELAP I'll keep the picture handy. smily_headphones1.gif

The rigid cut off disk worked perfectly, it's one of those little stone disks as round as your thumb that requires a mandrel.

With it cutting so flush you don't need any tape on the tube.

Now I just have to be careful plugging it in, with the missing pins it has no key now. biggrin.gif
post #3308 of 10502
That's right gibosi your using the 6DJ8's, I had it in my mind your were using a 12A?7 type tube. So all that heater stuff doesn't apply...

Well I'm batting 0 for 2 tonight, I guess it's time to just listen a little Genesis before bed, "Foxtrot" I'm thinking will suffice.
biggrin.gif
post #3309 of 10502
On a lighter note I have 4 Svetlana 6Ж5П's on their way from Sofia, another 3 week wait... biggrin.gif
post #3310 of 10502
Quote:
Originally Posted by TrollDragon View Post

Hey AFB!

MIKELAP sent me a picture of what is your MK IV SE's board section, there is a Linear 1084 modded in on a heat sink. Is this stock or a mod you have done? Possibly a CCS implementation? The input caps are missing as well. Do you have any full pics of the board?
beerchug.gif

 

Linear 1084? Heat sink? Modding? Nope, not me lol, my IV SE is pretty much stock!

post #3311 of 10502
Quote:
Originally Posted by mordy View Post
 

Hi Gibosi,

 

"Ah yes, it appears you have a pair of Toshiba-made 6CS6. These are nice tubes. :)"

 

 

I have a pair of Raytheon 6DT6A made in Japan plus the Siemens Foreign  EH90 and Haltron 6CS6. They all look like they were made in the same factory. Since we know know that there is a connection between Hitachi and Raytheon, how can you know if all these tubes were made by Hitachi and not by Toshiba? (Perhaps Toshiba made them for Hitachi when it comes to the Raytheon tubes?)

 

Have not been able to find out much about the production and differences between the Toshiba and Hitachi tube factories.

 

The bottom line is that these are all very nice tubes.

 

Mordy,

 

Oskari made a pretty very convincing case that these 6CS6 were manufactured by Toshiba. But of course, it is certainly possible that there was some kind of connection between Toshiba and Hitachi at that time....

 

http://www.head-fi.org/t/563884/little-dot-tube-amps-vacuum-tube-rolling-guide/2655#post_9756591

post #3312 of 10502
Quote:
Originally Posted by Audiofanboy View Post
 

 

Linear 1084? Heat sink? Modding? Nope, not me lol, my IV SE is pretty much stock!

 

No problem good sir, this was the pic in question. :D 

The TO-220 case LT1084 surrounded by the thick white silk screening there has been moded to fit.

It's a 5V 7.5A Low Drop Out Regulator that will keep Vout constant down to a 1V Vin/Vout differential.

Installed as a Constant Current Regulator possibly, or just a more effiecent 5V regulator most likely.

 

Anyway, as they say "Inquiring minds want to know..."

:beerchug: 

 

Edit: Update I found the picture, should have done a reverse Google first... It's eboy2003's MK IV from 5 years ago which has a different board than mine, probably a very early revision.

 

Here is the thread where the pictures come from and he has done some interesting mods, I'll have to give it a read through.

 

I just put the sudo repaired 6AV6 in and I am going for coffe and a smoke before I light it up and see if there is any flames. :D


Edited by TrollDragon - 10/5/13 at 7:09am
post #3313 of 10502

Update on the 6HM5s (Yugoslavia?!)...

 

Despite the blinding flashes still on start-up(!) - but with no obvious ill-effects after 50+hrs - these have definitely knocked the RCA 6DT6As off their perch. Initial reservations have been totally kicked into touch. I have now become an avid fan of really wide and deep soundstage, even though I thought it at first a rather less "intimate" sound. I love the 'airiness' and clarity these babies are putting out. And the range and 'cleanliness' of treble notes, coupled with extra instrument separation is truly a revelation. This separation probably also explains my initial doubts over bass response - what I thought may be a negative, ie less perceived 'slam', I now realise may be down to a much more subtle reproduction of different TYPES of lower frequency...ie a nice spread, rather than 'bunched', which at first can seem less weighty.  Perhaps these tubes are not for heavy head-banging - unless you turn that knob right up! Then again, I am a firm believer that less is more as far as bass is concerned - there are so many fine, detailed things going on in a really well-recorded piece of music that it is bordering on the criminal to overpower them indiscriminately...just my personal thoughts, that is...But despite my ramblings, please don't get the wrong impression - bass is lovely and rich from these tubes. Give 'em a try! And the beauty of these also is they are just "plug 'n play" (EF95).

 

Happy rolling.

post #3314 of 10502
Quote:
Originally Posted by mordy View Post
 

I have a pair of Raytheon 6DT6A made in Japan plus the Siemens Foreign  EH90 and Haltron 6CS6. They all look like they were made in the same factory. Since we know know that there is a connection between Hitachi and Raytheon, how can you know if all these tubes were made by Hitachi and not by Toshiba? (Perhaps Toshiba made them for Hitachi when it comes to the Raytheon tubes?)

 

How does one know anything for certain? :rolleyes:

 

Photos please!

 

The Raytheon–Hitachi relationship hardly precluded Raytheon from selling tubes from other sources.

post #3315 of 10502

I have a general question, what is the most detailed and dynamic tubes out there for the Little Dot 1+?

Tubes that blow the ones mentioned in the original guide out of the water.

 

I would like mod-less, to easy to mod tubes if possible.

 

Any ideas?

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