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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 291

post #4351 of 10509

Hi All,

 

Enjoying listening to an octal Sylvania 6SL7WGT tube, maybe from January 1952 or more likely 1962 (date code A2B). Not as super detailed as the 6DJ8 family, but very sweet and musical and non fatiguing.

 

Since the 6SL7 is the American equivalent to the Russian 6H9S/6N9S tube, did I partially upgrade the MKIII to the MK9 Little Dot amp?

 

Here is the advertising for the MK9 (English needs improvement):

 

  • Little Dot MK9 is that uses a electronic tube as a headphone amplifier. It uses 3 tubes (before: 6N9P, after class: 6080*2) were used as two stereo left and right channel amplifier. The input signal is the audio signal from the CD player or decoder, an amplified output signal used to drive headphones. The machine also has a road as a RCA signal output by the first stage, supply other amplifier as before use.
  • MK9 uses tube amplification circuit in the electronic is relatively rare in the SEPP single ended push-pull, OCL no output capacitor direct coupled power amplifier circuit.
  • The circuit output dynamic than the cathode output generally large (undistorted swing: 30Vp-p), due to the cancellation of the output capacitance, low frequency response can dive deeper, more solid, soprano Alto can be more transparent.
  • But to make the circuit in the case of direct coupled DC level is zero, need symmetrical supply complex. In order to stabilize the operation of the circuit, and the machine also adopts a "zero servo tracking circuit".
  • In order to ensure the safety of the output load, relay protection circuit and output protection special chip. The machine output tube uses a new production of the United States of America RCA company 50 years Antique Tube (ONS), is one of the best sound similar tube in the world.

 

(The 6080 RCA tubes are rated at 6.3V and 2.5 A and are plentiful on Ebay for $10 or less. )

 

Is it possible to add the protective circuit so that I can use a DC coupled ss amp with the the MKIII? It would have to be an outboard plug in style chip since I am not capable of opening the amp and solder in a circuit.

61lus4DYYSL._SL1500_.jpg 

post #4352 of 10509
Quote:

Originally Posted by mordy View Post

 

Is it possible to add the protective circuit so that I can use a DC coupled ss amp with the the MKIII? It would have to be an outboard plug in style chip since I am not capable of opening the amp and solder in a circuit.

 

+1 to that question!

 

Wouldn't just adding a large value coupling capacitor (?) on the output of each channel basically cancel any DC offset - and therefore offer a bit more protection and de facto compatibility with non DC couple amps?

post #4353 of 10509
Quote:
Originally Posted by Audiofanboy View Post
 

 

+1 to that question!

 

Wouldn't just adding a large value coupling capacitor (?) on the output of each channel basically cancel any DC offset - and therefore offer a bit more protection and de facto compatibility with non DC couple amps?


I have a nice little box coming from AskewLabs with just such an arrangement configured. It will have RCA In/Out jacks with an A/B switch to compare the sonic differences with the protection circuit engaged or in pass through mode, as the circuit will minimally alter the sound out of the amp.

 

This box will provide DC protection so anyone can safely connect the Little Dot's Line Out to an amplifier or receiver. When this box arrives I was planning on setting up a tour like they do with headphones, those interested could have the box mailed to them, try it out for a while and then mail it to the next guy on the list. After the trial if you feel it is something you want you can either build your own or order one all ready to plug and play.

 

It won't be here until the new year and I will let everyone know when it arrives.

:beerchug:

post #4354 of 10509
Quote:
Originally Posted by TrollDragon View Post
 


I have a nice little box coming from AskewLabs with just such an arrangement configured. It will have RCA In/Out jacks with an A/B switch to compare the sonic differences with the protection circuit engaged or in pass through mode, as the circuit will minimally alter the sound out of the amp.

 

This box will provide DC protection so anyone can safely connect the Little Dot's Line Out to an amplifier or receiver. When this box arrives I was planning on setting up a tour like they do with headphones, those interested could have the box mailed to them, try it out for a while and then mail it to the next guy on the list. After the trial if you feel it is something you want you can either build your own or order one all ready to plug and play.

 

It won't be here until the new year and I will let everyone know when it arrives.

:beerchug:

 

Nice! So, wait, you're talking about what essentially a custom-made DC-offset cancelling box right? I'm curious as to how much such a contraption would cost to have made?

 

What's actually in the box, btw? Am I totally wrong in thinking it's basically large caps lol, or do I at least have the basic idea down?

post #4355 of 10509
Quote:
Originally Posted by Audiofanboy View Post
 

 

Nice! So, wait, you're talking about what essentially a custom-made DC-offset cancelling box right? I'm curious as to how much such a contraption would cost to have made?

 

What's actually in the box, btw? Am I totally wrong in thinking it's basically large caps lol, or do I at least have the basic idea down?

I'll have all the details when the box arrives and I doubt it will be too expensive.

 

I don't know the exact circuit but I imagine it will have some nice quality caps of what value I don't exactly know, he has calculated the minimal effect on the output as much as possible while still providing protection.

:beerchug:

post #4356 of 10509
Quote:
Originally Posted by TrollDragon View Post
 

I'll have all the details when the box arrives and I doubt it will be too expensive.

 

I don't know the exact circuit but I imagine it will have some nice quality caps of what value I don't exactly know, he has calculated the minimal effect on the output as much as possible while still providing protection.

:beerchug:

 

Yeah, I always wondered if I could just solder some appropriate caps, like, directly on each output RCA cable going to the power amp(s), so any DC offset would just get cleaned up nicely. But every time I thought about actually trying it out, a blinking red light turned on in my head, and a voice too: "Thou shalt not maim thine interconnects in vain! Especially if thine electrical knowledge is so limited!". So, yeah, that stopped me from doing it lol; but I might consider it again depending on how your crazy contraption works - and how hard it is to make, I'll solder a cap or two but not a box full of electronics...

:beerchug:

post #4357 of 10509
Quote:
Originally Posted by mordy View Post

Hi CollectoR13,

Buy these tubes from Yugoslavia; offer $4 or $5 each - free shipping. Asking price is $6.95. Look up on Ebay:

6HM5 /6HA5 / EC900 export quality audio triode tube / NOS / FREE SHIPPING /




As a bonus you will get a 1 second fireworks display when you turn on the tubes. (Don't worry, they are designed to flare up for quicker start, and it will not damage anything)



I would be able to get some made by sylvania for cheap.
Are they good too or maybe better?
post #4358 of 10509

Seriously I have tried them all, except for the supermod tubes (adapters etc..). The yugo 6Hm5 is by far the best for unmodded tubes in my gear. A close second are the Lorenz EBC91 however you need to cut some pins.I say get both and let us know which you think are the best.

post #4359 of 10509
Quote:
Originally Posted by TrollDragon View Post
 


I have a nice little box coming from AskewLabs with just such an arrangement configured. It will have RCA In/Out jacks with an A/B switch to compare the sonic differences with the protection circuit engaged or in pass through mode, as the circuit will minimally alter the sound out of the amp.

 

This box will provide DC protection so anyone can safely connect the Little Dot's Line Out to an amplifier or receiver. When this box arrives I was planning on setting up a tour like they do with headphones, those interested could have the box mailed to them, try it out for a while and then mail it to the next guy on the list. After the trial if you feel it is something you want you can either build your own or order one all ready to plug and play.

 

It won't be here until the new year and I will let everyone know when it arrives.

:beerchug:

That would be  great i could now use the Littledot as preamp with my Pioneer SX 750 nice .Here we go again!

post #4360 of 10509

Hi Collecto R13,

 

I don't have experience with the Sylvania 6HM5 so I can't tell if they are good or not. However, I do know that the EI 6HM5 Yugo tubes are very good, and you can use them unmodded. If you don't want to go to the 12AX7/6DJ8 or octal 6SL7 families that would be my first choice. In addition, they are very inexpensive as premium tubes go.

 

However, building the adapters for the above mentioned tubes will take your LD amp to new heights with a very significant improvement. As they say in the car rental business - a triple upgrade....

post #4361 of 10509

If you want a good subwoofer very cheap, here is an excellent deal:

 

http://slickdeals.org/permadeal/109700/newegg---polk-audio-psw10-10-powered-subwoofer-black

 

This a Polk PSW10 50W self powered subwoofer for $50.00 including shipping (usually no sales tax). Sold by Newegg which is an A+ company.

post #4362 of 10509
Quote:
Originally Posted by CollectoR13 View Post


I would be able to get some made by sylvania for cheap.
Are they good too or maybe better?


I have the Sylvanias and they are excellent

post #4363 of 10509
Quote:
Originally Posted by CollectoR13 View Post


I would be able to get some made by sylvania for cheap.
Are they good too or maybe better?

I find the Yugos good, but they have little bit "metallic" sound in my gear. 
Sylvania 6HM5 has very good highs and very pronouncive bass, but they can sound little bit "crowded" in upper mids/highs.

post #4364 of 10509
So, I think I am going half octal now smily_headphones1.gif
I will buy a Adapter for Power tubes 6n6p to 6sn7, but the one that was available on eBay seems to be not available anymore...
What would you recommend as a good 6sn7 Tube (endgame?)?
And sure I am getting some yugo 6hm5s wink.gif
post #4365 of 10509
Quote:
Originally Posted by CollectoR13 View Post

So, I think I am going half octal now smily_headphones1.gif
I will buy a Adapter for Power tubes 6n6p to 6sn7, but the one that was available on eBay seems to be not available anymore...
What would you recommend as a good 6sn7 Tube (endgame?)?
And sure I am getting some yugo 6hm5s wink.gif

 

The General Electric 6HM5 made by Mullard in Great Britain is also a very good choice, IMO. :)

 

``````````

Some on this forum have experience using the 6SN7 as a driver tube, but I do not think I have seen any postings about using it as a power tube. You may be one of the very first to do this....

 

As to an end-game 6SN7, if you go by price and internet reputation, then it would have to be the Tung Sol with black glass and black round plates, such as these:

 

http://www.ebay.com/itm/PAIR-VT231-NOS-TUNG-SOL-6SN7-1940s-6SN7GT-TUNGSOL-/171120565209?pt=Vintage_Electronics_R2&hash=item27d7949bd9

 

I have yet to try a 6NS7 (driver tube), but have an inexpensive National Union coming to me.....

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