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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 15 Dec 2013, 17:19 
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Joined: 06 Apr 2009, 10:08
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Location: US Pacific Northwest
As promised, here are the load line designs for the 5 different tubes in order of increasing gain.
Attachment:
12AU7 4SU.jpg

Attachment:
12AV7 4SU.jpg

Attachment:
12AY7 4SU.jpg

Attachment:
12AT7 4SU.jpg

Attachment:
12AX7 4SU.jpg

As always, question and/or comments are more than welcome.


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PostPosted: 16 Dec 2013, 09:33 
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Joined: 05 Jun 2012, 13:10
Posts: 196
Location: Darboy, WI, USA
Thanks to Matt and everyone for this community and the body of work that is developed by it. It truly is a joy coming here, learning and building!

My last couple of components will be arriving today, weather permitting, for my 4S Universal preamp. I just need to find a chassis...

I will be using Matt's tube power supply as opposed to Mark's solid state design. Hopefully I'll have time before Christmas to finish it. (Then on to my 2A3 EH Gold build...)

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Ross in Wisconsin


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PostPosted: 26 Dec 2013, 08:20 
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Joined: 22 Nov 2011, 21:35
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I built a unit using Matt's PSU today. I am a tube amp beginner and would like learn more charactistics of valves, this schemetic and Matt's testing result is very helpful to me.

Attachment:
SAM_1205.jpg


Attachment:
SAM_1206.jpg


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PostPosted: 26 Dec 2013, 12:40 
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Beautiful Build! :thumbsup:

How does it sound?

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PostPosted: 26 Dec 2013, 22:36 
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Joined: 22 Nov 2011, 21:35
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The sound is clear and dynamic :P . I would like to reproduce your results with my unit, but I don't know what equipments should I need? I have a multi-test meter, an audio generator and an oscilloscope.


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PostPosted: 27 Dec 2013, 20:19 
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ckleung17 wrote:
I would like to reproduce your results with my unit, but I don't know what equipments should I need? I have a multi-test meter, an audio generator and an oscilloscope.
If you mean the gain and phase plots, what you really need is a signal generator, an oscilloscope, and, if possible, a good AC voltmeter. Your multi-test meter will not really help because they will generally only produce accurate AC readings at 50Hz to 60Hz. Even the True RMS volt meters like the Fluke 179 are only specified to measure AC voltages from 45Hz to 500Hz. If you look at the picture of the unit under test on the project page, you'll see the Leader LMV-185A Dual AC voltmeter that I use. This unit is specified to produce readings accurate to 2% from 20Hz to 200kHz

The best way to take the gain measurements if you don't have a wide-band AC voltmeter is to read voltages directly off of the oscilloscope. Just make sure to periodically zero the inputs to make sure that the traces are still baselined to zero volts. The phase measurements are slightly more problematic. The way I did it was to use a plotting compass and take measurements of the relative zero crossings between the input and output waveforms accounting for the 180deg mid-band phase shift. If you take a measurement, divide it by the length of one full cycle, and multiply by 360, you get the relative phase shift in degrees. Then just repeat both procedures at a number of frequencies to generate the response plots.

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PostPosted: 30 Dec 2013, 18:01 
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Location: Australia
ckleung17 wrote:
I built a unit using Matt's PSU today. I am a tube amp beginner and would like learn more charactistics of valves, this schemetic and Matt's testing result is very helpful to me.

Clean and neat build, very smart.

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Projects:”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp | "LeManja” - hybrid tube and chip headphone amp


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PostPosted: 31 Dec 2013, 02:33 
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I test for maximum swing in volts before clipping and +\- 3db frequency points. Also noise level. 3db points at least 20hz to 20khz swing, anything??? and noise under 2.5mV. At low output voltage levels distortion is generally around 0.6% for these preamps. A two stage tube preamp with feed back I built some time back never got over 0.05% distortion even driving into heavy loads at large voltage swings. But these sound better.

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PostPosted: 17 Jan 2014, 17:38 
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Joined: 03 Dec 2013, 02:03
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About how much in parts would this cost to build?

Being a noob, a parts list would be helpful. At least for suggested caps, resistors, and transformer.

Thanks!


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PostPosted: 17 Jan 2014, 19:21 
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Depending on your enclosure you should be able to builds the preamp for a few hundred dollars. This is based on a very cheap or free enclosure (use something at hand) and a wall wart AC supply. I use a bride rec for HT and generally supply DC to heaters. Use a small step down tranni backwards to generate 240V of AC from a 24V wall wart.

I always make list of parts direct from the schematic. Then draw my own PS and list parts for that.

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