[bearington]

I have those adapters but they will not fit.  I am using a SOIC-8 soldered to the top and bottom, http://cimarrontechnology.com/so8to8-pindipadapterpn970601-3.aspx  has them already made, or you can make your own.

The pots settings I used was based on the opamp I used, I put my meter between GND and the outputs of the op amps pins 1 and GND and pin 7. I never got to put it on a scope to see what was the best setting, but I am very happy with 6.28 to 6.30, it is kind of the lowest setting. Before you do this, measure the two points and see what the voltages are before you start. Let me know what they are. I forgot to do that.  The last thing I did, was install a few bypass capacitors. If I get a chance, I will install a few 50pF caps on the opamp as the data sheet of the chip recommends for the lowest distortion.

Current Tube       Semens Silver Plate
Current OpAmp   Two AD767 on a BrownDog Adapter
Bias set to 6.28 volts DC. 
Bypasses Coupling Cap with a Vishay poly .1uF cap (just for fun)
 
Still don't have a whole lot of time, to really play... but do a little once and in a while 

 

[MDR30]

Opened the Muse to check the bias.
 

 
You just remove the tube, pull out the volume control knob, unscrew the four screws on the back plate and take the board out.
 

 
Here are the bias measure points (pin 1 and 7), and the adjustment pots (P). You place one probe on the pin, and one on the phono socket (ground).
 

 
Stock voltages were at 7,22 and 7,24 volts. I adjusted both to 6,30 volts at bearington's recommendation.
 

 
Also soldered a ground lead. It locks between back plate and box.
 

 
Sound possibly became a bit smoother after the adjustment.

 

[MDR30]

Quote:

awesome work Bearington.... however for a $100 and all that work I don't think it's worth it...
 
I also purchased this little beast: 
 
http://www.ebay.com/itm/261031079874?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
 
It's about $50 and I had to troubleshoot the transformer to make sure I got the right voltages, but at least it came assembled...... MAN this thing sounds AMAZING!!!! much better than "The Quickie" which was $100 and I had to assemble the whole thing and it didn't even come with a box!!!
 
K7

 
Is it as powerful as the Muse TU-20? Still sounding good?

 

[K7music]

@MDR30.
 
Interestingly enough, I tried to run a pair of headphones with that specific 6N3 preamp and it wouldn't do it. However I don't care too much for headphones.. I just ran it into my cheapy "Audio Source A-100" amp and into a pair of Paradigm Atom 2's. 
 
To answer your question..... I'm not sure if the 6N3 preamp is AS powerful because it can't run a pair of headphones.... (maybe I wired something wrong, and didn't care to correct it), but the fidelity is the best I've heard so far..... MUCH cleaner than the Muse TU-20.
 
Another thing I discovered though, is that just after a few weeks of listening to the 6N3, the channels started unbalancing... then I learned that if you have a solid state rectified supply that you have to have an ON-Delay for the plate voltage to eliminate "Cathode Stripping", which is basically unnecessary wear and tear. 
 
K7.

 

[MDR30]

"Interestingly enough, I tried to run a pair of headphones with that specific 6N3 preamp and it wouldn't do it. However I don't care too much for headphones."

K7.
[/quote]


Right. Well maybe you should edit your first post before someone buys it thinking it's for headphones. This is after all the Headphone amp forum.

 

[bearington]

  I did a couple of other things, kind of quickly. The cool part about this little tube amp is that I can open it, solder up some parts and close it very quickly. I added Bypass caps to the Coupling caps, and to all the electrolytic capacitors near and behind the tube, on the bottom of the board. It was hard to get them to fit, but I got them in. I haven't listened to it yet, I have them burning in. I think I might make sure the opamps are "A" Biased and put two 50pf caps on the output to pos power as indicated in the AD767 Data sheet for reducing THD. Just to do and see how it sounds.  

 

[MDR30]

And the 6V tube heater supply had a nice 1.2V ripple of around 20kHz, but that's also typical of those cheap little LM7806's... more filtering is in order in my opinion. 

K7.

Is there an alternative to the LM7806 to get a cleaner supply voltage?

 

[MDR30]

  I did a couple of other things, kind of quickly. The cool part about this little tube amp is that I can open it, solder up some parts and close it very quickly. I added Bypass caps to the Coupling caps, and to all the electrolytic capacitors near and behind the tube, on the bottom of the board. It was hard to get them to fit, but I got them in. I haven't listened to it yet, I have them burning in. I think I might make sure the opamps are "A" Biased and put two 50pf caps on the output to pos power as indicated in the AD767 Data sheet for reducing THD. Just to do and see how it sounds.  

Any improvements? Photos of your board would be welcome, to see where you put all those caps.

 

[K7music]

To be honest, I might have made some erroneous measurements because I had the scope on 10:1 setting and probe at 1:1 setting..... so that 1.2Vpp ripple was probably a 120mVpp ripple.... still a lot thought and the device still sounded pretty bad... 
 
I'm not sure what could be subtituted for the 7806, but more filtering caps are definitely in order. 
 
I don't have the preamp with me, I lent it to a friend. 

 

[MDR30]

There was a distinct difference when lowering the bias from 7,2 to 6,3 V. Maybe some nice distorsion that gave the sound an edge disappeared. Riding that voltage close to the border may be the trick. I don't have an oscilloscope, but someone who has could probably find the right setting.
 
In the meantime I got myself some op amps and a tube to try out next week.
 

 

 

[MDR30]

At least tried the AD797AR op amp and sound is more vivid and transparent. Not much difference between the Russian Electro Harmonix and the Slovakian JJ 6922 tubes, they both sound fine.
 
Gonna let it settle for a while before I do some more comparisons. But it's making wonderful music with my K400 (this week's preference) with astonishing clarity and size of sound stage.
 

 

[MDR30]

It's all warmed up and sounding good now after a few days. This is a powerful little amp - plays loud, clear and full. Best 50 bucks I spent.
 
Didn't realize that the little perspex window filled a purpose: to identify the op amp. Here's the little bugger:
 

 

[MDR30]

Quote:

For the size, cost it sounds good, using customized denon ah-d2000, but will try my stock hd800s tomorrow. The Er4s sound good too. The source is a ak100 on the line ins on the back, or an imoded iPod on a custom dock. Currently this is the best sounding tube and op amp combo I tried, have many more tubes and op amps to audit. I need put this on a scope to find the best grid voltage ( no over modulation ). I also have an occasional noise that comes and goes, need to get rid of, other then that dead silent at full volume ( other then typical tube noise at extreme volumes. )

 
 
How did it do with the HD800? I'm also wondering if it's just to remove the blue LED or if it's in circuit and needs some sort of replacement.
 
My amp sounds fine, listening to it a lot on side with the G3, both have their merits.

 

[bearington]

  I actually have that little amp with me on the road. I carry a Corda 2Stepdance with me and it is my favorite potable amp. The HD800 sounds good with everything. This little tube amp was just a toy to play with. The AD797AR and my APEX tube sounded best, with a clean bias setting. I find the impedance match is better with the line in ports on the back. I have placed poly bi-pass caps across every capacitor to reduce noise and replaced the power supply with a much better unit. I think I got the best I can get it to sound, and have not really played with it much. There really isn't enough power to drive the tube to it's potential other then over modulation.

 

[MDR30]

Just thought I'd follow bearington's mod to allow swapping with 12AU7/ECC82 tubes as well.
 
The board has jumper pins installed for either 6 or 12V tubes.
 

 
The jumpers are soldered for the supplied 6V Electro-Harminix 6922 tube on the backside of the board.
 

 
Desoldered it.
 

 
Jumper in place. Now its easy to change from 6DJ8/6922 (not 6622 as the board is wrongly labelled) to 12AU7/ECC82.
 

 
Running it with fine sounding AD797 op amps on a double sided adapter.
 



 
Coming up for trial: Mullard ECC82.