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audiofanboy said:

The Tung Sol 6AJ5 was a very nice tube with a guaranteed pleasant listen, but like many 6AK5-ish tubes, I had ultimately found it lacked the absolute details and was a bit soft on the attack. Again, after testing so many other tube types, I just can't see a single reason to go back to the 6AK5 family... This was already somewhat the case for me after spending time with the CV4015...

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This!
 
 
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Originally Posted by mordy 

The next logical step is to write to David ZheZhe and ask him to design the Little Dot MkIIIi AFB edition with built in switches for the 6AU6 tubes. A little toggle switch on the front or the back panel would be a nice touch (no more dealing with pesky jumpers).

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And this!
Also, include the other families of tubes as compatibles, which are workable with the EF91/92 jumper setting, as e.g. the 6EW6.
 
So, I am going to get a pair of 6AU6s after all the discussion. Curiosity wins.

David should give you all with free products for all your hard work documenting what's compatible with his product line!

it certainly had way more value in my eyes after trying all these new awesome tubes!

Dear A11,
 
You won't regret getting the 6AU6 tubes. Please let us know your impressions once you've tried them.
 
My Tektronix have now been on over 24 hours non stop. At this point they have mellowed out a little with the too bright edge in the treble gone. They also run cooler than the RCAs.  When I drag in other family members into my listening room they all notice the crispness and impact of the presentation (OK - so I demo a drum solo at full blast).
 

Hard to not get intoxicated by you guys

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acapella11 said:

Hard to not get intoxicated by you guys

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I have been wondering how long it would take you to finally jump in! And as you will soon see, the water is fine! LOL

About jumping in - you need the jumpers for the sockets. I am sure that you are going to research the benefit of using 100% OFC multi stranded 30 gauge pure copper wire. However, in case you don't have this (like me), take a look inside an old abandoned PC computer case and see if there is a thin wire connector there - there should be plenty of choices.
My wire is silver stranded and once put in place with a tweezers works just fine - I don't think it's even copper.
 
Good luck!
 

And to give you another option, I have been successfully using solid core 30 gauge wrapping wire. I would guess that as long as it is sufficiently small, most any wire will work.

Here is the stainless steel anti static tweezers (for changing jumpers) on sale with a coupon code for 60c including shipping and tax. If you want it don't wait to order it, because it will be gone. Make sure to use the coupon code and check free shipping.




http://www.meritline.com/high-precision-anti-static-stainless-steel-tweezers---p-43059.aspx?strcoup=MLCKA05WNL1&dealid=55393

Thanks Mordy and Gibosi for the ideas. I searched through my old PC inventory and of course there were lots of cables. I found a thin one, which was from an internal output of a network card, guess no one would ever use that again. So, I got two jumpers ready. My pointy nose pliers seem to work fine changing them. Now, I just need the tubes to try them.  

As promised I have tried to compare my 8425A/6AU6s and my 6136/6AU6WBs, both manufactured in the mid 1960s by GE.
 

 

As you can see, there are some structural differences. Obiously, the 6136s have black plates with two squarish holes while the 8425As have gray plates with three roundish holes. Also, of interest, the 6136s appear to have two layers of mica, top and bottom, compared to one layer for the 8425As. Other than that, these tubes appear to be virtually identical to my eyes.
 
To audition these tubes, I used a few tracks off of Eric Clapton's Unplugged album and another track I have grown very fond of, Ain't Nobody's Business with Willie Nelson and Wynton Marsalis:
 
https://www.youtube.com/watch?v=aDJIwVPimyg
 
These tracks have real instruments and real voices in real spaces, I would hope that they would be able to reveal any sonic differences, providing my test and measurement apparatus - "rusty ears and cheap gear" - are sophisticated enough to recognize them. LOL 
 
Playing through these tracks, as I feared, my testing apparatus was unable to discern any sonic differences. However I think it is worth pointing out that both of these are premium tubes manufactured by GE in the same time frame, so one could postulate that they may well share a very similar sound. I am hopeful that others of you, with better ears and equipment, will have a chance to listen to these and let us know your impressions. To my ears, both of these are very fine tubes. Highly recommended.
 
Curiously, I have been burning in a pair of Tung Sol 6AU6WAs from the mid 1950s and I do believe that the mid range on these Tung Sols seems to be just a bit more forward than the GEs... but I fear I may be getting tired...  so I should spend more time with them to be sure....
 

 

Quote:

acapella11 said:

Thanks Mordy and Gibosi for the ideas. I searched through my old PC inventory and of course there were lots of cables. I found a thin one, which was from an internal output of a network card, guess no one would ever use that again. So, I got two jumpers ready. My pointy nose pliers seem to work fine changing them. Now, I just need the tubes to try them.  

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I have some 6AU6W tubes on the way and need to figure out something for the jumper. I guess the PC cables used to power on floppy discs, cd, dvd, hd, etc. (taking one of the 4 wires) are still too big to fit in the socket, correct ?
What about "sacrificing" some unused earphones (e.g. stock ones that came with sansa clip+) ? The cable going to to each earpiece should contain 2 wires small enough to be used as jumper (or are they too small) ? 

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vic2vic said:

 
I have some 6AU6W tubes on the way and need to figure out something for the jumper. I guess the PC cables used to power on floppy discs, cd, dvd, hd, etc. (taking one of the 4 wires) are still too big to fit in the socket, correct ?
What about "sacrificing" some unused earphones (e.g. stock ones that came with sansa clip+) ? The cable going to to each earpiece should contain 2 wires small enough to be used as jumper (or are they too small) ? 

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I have used 28 gauge stranded wire, 28 gauge solid core wire and 30 gauge solid core wire. I wonder if your headphone wires are smaller than that? But even so, I seriously doubt that they are too small. Usually the problem is that the wire is too big preventing the tube from seating in the socket properly. So I would say go for it!

More on blackplate GE 6136/6AU6s...
 
I had another pair of black plate GE 6136s arrive today. These are not 6136/6AU6WB tubes, just standard 6136.
 

 

But they look identical to my 6136/6AU6WBs, even down to the double thickness of mica. Judging from a visual inspection, there is no significant difference between these newly arrived standard GE 6136 and my 6136/6AU6WB.
 
With their arrival today, I began to look more closely at my 6136/6AU6WBs and discovered that this "matched" pair are not exactly the same:
 

 
 

 

 
Notice that one has two squarish holes and the other two roundish holes. Moreover, one has etched "6136" and the other "6136 USA". So there is some variation, but in the end, these all appear to be the same tube.
 
As some of you may be out there searching for these, thought this little bit of info might be helpful....

While many of you have Little Dot IIIs and IVs, I have a Little Dot 1+. The LD1+ is a hybrid/tube amp. That is, the tube stage sits in front of a solid state amplifier. But the difference is actually quite a bit deeper than that. In the III and IV, the driver tube is used as an amplifier to provide gain. In the 1+ the tube stage provides no gain, and in fact, actually provides a slight negative gain. The tube finds itself in a cathode follower configuration and thus the output is something on the order of 1, 2 or 3% lower than the input. Thus, the tube stage acts as a buffer, and not as an amplifier. In fact, the tube stage can be completely bypassed with a straight wire, and the amp will work absolutely fine, but as a solid state amplifier.
 
One consequence of using the tube stage as a buffer, and not as an amplifier, is that the 1+ can use tubes that would likely be completely unacceptable in the III/IV. A couple of pages ago, you might remember that I tried out a 6BA6. This is a remote-cutoff pentode that likely would distort very badly if used in the III/IV.
 
So why am I telling you this? LOL.  Well, I never really thought the 6BA6 would be a great sounding tube. I found a pair of 1947 NIB/NOS 6BA6s. Why did that get my attention? Well, I was born in 1947, and I thought, how cool would it be if I could run these in my Little Dot? So I ordered some cheap ones first, to make sure I wouldn't be wasting my money, and they actually sounded pretty good. Not 8524A good, but still pretty good.
 
And so.. here are my new treasures:
 

 
 

 
 

 
They are in better shape than I am! LOL

Sunday afternoon, I was able to spend more time with the 1956 Tung Sol 6AU6WAs.
 

 

Using the GE 8425As as my reference, I allowed myself to be serenaded by Eric Clapton, Willie Nelson and Winton Marsalis. At first, I though the Tung Sols were just a bit brighter, more air, but then I realized that the midrange, horns and vocals, were a bit more subdued. Otherwise, they have the classic 6AU6 sound, clean, detailed and powerful. I prefer the warmer sound of the 8425As, but if others find those too warm, the Tung Sols might be a good choice.
 
Next up, two pairs of 1950s Sylvanias:
 

 
 

 
I noticed that the plates and getters are different in these two pairs, even though manufactured only three years apart.....

 
Like Mordy, I often write to the eBay vendors. I ask lots of questions. And some of them are quite friendly and others are not so friendly, to put it politely. LOL. The vendor I purchased the GE black plate 6136/6AU6WBs is one of the friendly ones. He was very interested to learn I was using these in a Little Dot and he offered that he might have some interesting 6AU6s for me. And sure enough, I now have these Tung Sols and Sylvanias.
 
The Sylvanias with red are burned in and have started to burn in the second pair. Hope to be able to post some impressions in the next day or two.