[Niteshade]

A sweet Amplifier with the following specifications:

1. 50 Watts x 2 into 4 or 8 ohms
2. DC Biased (Set up to be extremely easy)
3. 20-20,000hz response
4. Tube regulated high voltage (the extra 6L6) ***THIS WORKS GREAT!!!***
5. Schmidt Phase Splitter
6. 5x 6L6 & 2x 6SN7 (or 12AX7)
7. IEC Power Socket
8. ZERO Feedback of any kind!
9. Choice of colors is FREE!
10. 400 watts total power supply
11. Point to Point wired using high grade tube amp wire
12. Edcor output transformers

Sonic Observations:

Extremely transparent. High frequencies are not rolled off in the slightest, the midrange is full, but linear and pleasant. Bass is fast, abundant and accurate. Works great with inefficient or efficient speakers. The lack of feedback allows the amplifier to produce an unprecedented froward sound stage with pinpoint imaging and centering.  Tubes all run cool, more so than you may be used to. We didn't notice any shortcoming with regards to the genre of music played. Pop-Rock, country and classic all played flawlessly. The amp showed no favoritism for any of them.

[MaxCast]

What's it cost to replace the tubes in that there amp?
Amp cost?

[mcullinan]

I think designwise it might be nicer to stagger the tubes. Push the 2 6ns7s and center tube forward.
Mike

[pardales]

What are some of the chases colors?

[DARTH AUDIO]

What parts are being used in this design?

[JoshK]

Looks cool.    I like the choice of 6SN7's over the pedestrian 12ax7/12au7.   

I am a curious as to how you obtain 50w out of 2 6L6's without nfb.  I am assuming the 6L6's are triode strapped or else gNFB would be almost necessary.  Not that I doubt you, just intrigued that it can be done.  Class A/B2?

Sounds like a cool amp.  With 6L6's, I bet it sound great too. 

[Niteshade]

I'm going to answer questions throughout the day, one at a time due to a lack of, "sitting down in front of the computer time". 

It will cost around $105.00 to replace all the tubes at once. Maybe a little more or a little less depending on what you're after. You'll get the best results using power tubes with 30 watt anodes.

[Niteshade]

"I think designwise it might be nicer to stagger the tubes. Push the 2 6ns7s and center tube forward.
Mike"

That's a very good suggestion. The tubes are positioned as they are now to make it easier for the power tubes to dissipate heat. Staggering them would work as well.

Future models will have different appearances and specifications. I tend to change things quickly when there's a benefit to it.

[zybar]

Just saw this on Audiogon:

http://cgi.audiogon.com/cgi-bin/auc.pl?ampstube&1224899737

George

[Niteshade]

"Just saw this on Audiogon:

http://cgi.audiogon.com/cgi-bin/auc.pl?ampstube&1224899737"


Thanks for copying the link. That's the first model out and is currently being used as a demonstrator. Demos are a great way to save money. $$$$

[Niteshade]

Amplifier colors:

Hammertone Copper
Dark Red Metallic
Piano Black
Semi Gloss Black
Dark Blue
Red
Hunter Green
Grey
Silver/grey Metallic
Rock Color (highly textured) - Brown or grey based

It's possible to go two-tone as well, meaning enclosure one color and transformers a different color.

[Niteshade]

"What parts are being used in this design?"

The output transformers are made by Edcor. Coupling capacitors are metalized polypropylene by Xicon. Wire is a high temperature cloth covered wire made for tube amplifiers. One filter cap is a JJ/Tesla and the other is a Nichon commercial series. The power transformer is a Hammond high end with a solid copper EMI shield. The enclosure is solid steel and powder coated semi-gloss black. Power supply diodes are rated for 1.2KV @ 3 amps.

[Niteshade]

"I am a curious as to how you obtain 50w out of 2 6L6's without nfb.  I am assuming the 6L6's are triode strapped or else gNFB would be almost necessary.  Not that I doubt you, just intrigued that it can be done.  Class A/B2?"

The NS-100 is using 60 watt output transformers that are a good match for the 6L6's. The phase splitters are well balanced too. From the combination, my watt meter says I'm getting 50 watts RMS at the point of clipping. There is absolutely no feedback of any kind- either local or global and the circuit is extremely stable. I was able to make it work by reducing the input sensitivity a little and by providing a regulated DC voltage to the phase splitters to reduce power supply noise. It is running between classes AB1 and AB2. Bias voltage is -35 volts.  High voltage is 436 volts.

Some info:
Typical Operation
(Values are for two tubes)   6L6   6L6GC
Plate Voltage   360   360   450   volts
Grid-No.2 Voltage   270   270   400
Grid-No.1 (Control-Grid) Voltage   -22.5   -22.5   -37
Peak AF Grid-No.1-to-Grid No.1 Voltage   45   45   70
Zero-Signal Plate Current   88   88   116   ma
Maximum-Signal Plate Current   132   140   210
Zero-Signal Grid-No.2 Current   5   5   5.6
Maximum-Signal Grid-No.2 Current   15   11   22
Effective Load Resistance (Plate-to-plate)   6600   3800   5600   ohms
Total Harmonic Distortion   2   2   1.8   %
Maximum-Signal Power Output   26.5   18   55   watts

[jon_010101]

At risk of sounding like a trouble-maker, I am going to second the 50W doubts.  30W at 1% THD is the best we've been able to do in pentode mode with 6SN7 driver without drawing grid current, and the 6SN7 can't supply it in this configuration.  We are using about the same operating point and Edcor iron. 

But, 6L6 = my favorite output tube. 6SN7 my favorite dual triode 

[Niteshade]

"At risk of sounding like a trouble-maker, I am going to second the 50W doubts.  30W at 1% THD is the best we've been able to do in pentode mode with 6SN7 driver without drawing grid current, and the 6SN7 can't supply it in this configuration.  We are using about the same operating point and Edcor iron."

Here's some more data:
Vp:               450 v
Vscr:             400 v
Grid bias or res. -37 v
Ip idle:          116 mA
Ip max:           210
Iscr idle:        5.6 mA
Iscr max:         22 mA
Load:             5600 ohms
Pout:             55
THD (approx)      1.8%

At 55 watts output, it appears the THD will be around 1.8%. These voltages and the load impedance are a little different than my circuit, but the THD level looks about right. Running the amp around 30 watts will produce less THD.

[JoshK]

just another fyi.  tungsol reissues for the 6l6gc and the 6sn7's are both suppose to kick ass.  these are modern production and easy to source for less than 150 for the whole shibang.   of course, nos is nice, but harder to get and more expensive.  i have heard some reports where the tungsol reissues beat tungsol nos.

[Niteshade]

Joshk brings up a mighty good point and I'd like to expand on it further: Due to the way the NS-100 is set up, tube rolling will provide different 'hues' of tonality. It's like having multiple tube amps in one. Different tubes have different characteristics and this amp will allow them all to display their characteristics flawlessly. I have upgraded the NS-100 circuit to a semi-automatic DC bias system that makes it simple to adjust the bias and dial in any 6L6 variety's best qualities.

[Niteshade]

I have added another feature to the NS-100 that works incredibly well: Auto tube balancing. It's almost like my hybrid biasing that uses fractions of both cathode and DC biasing, but leans more towards DC biasing. The result is a 'cushion' that's just enough to let the power tubes to self balance, but not enough to lower the output power. The bias voltage is still adjustable and it's easy to do. No meters or screw drivers are necessary.

[Niteshade]

We're installing variable negative feedback and an additional gain stage using a 12AX7.  aa


Photos coming soon as well as a revised description of the amp's performance and features.


***We are selling this demo/first production model on Audiogon for a  reasonable price. All the upgrades are FREE as well to make up for some of the cosmetic blemishes this unit has.