Is this OK for the Etude Preamp?

[cbutterworth]

OK, I am new to Tube DIY. I have looked at and re-drawn the schematic from DIYParadise Etude. Am I doing anything stupid with this schematic?

A search for the Etude, has revealed a number of posts, but things still seem rather complicated (at least for me).

I modelled the PSU in PSUDII with a resistive load of 12K and got 293V at B+

The transformer will be the Hammond 274BX with 375-0-375 at 172mA

The chokes will be 30H 595 ohm.

I am trying to understand the circuit, epsecially where the 12K resistor fits-in ie. what does it do?

Anyway, do the voltages look OK, and if not, how can I calculate them, what about current, etc?


Maybe, I should simply be asking - Is there a good reference book for a newbie?????

Charlie

[ErikdeBest]

Hi Charlie

This is a grounded cathode amplifier. I could try to explain how it works, but you may be better of reading it from John Broskie http://www.tubecad.com/articles_2003...ier/index.html

The 12k is the load for the tube, not the same as the load on the PSU. In PSUD you can change the load into a constant current. I would do that, and plug in the current drawn through the 12B4 (two times the current if you are building a stereo amp using a common power supply).

Hmm...besides the excellent articles by John Broskie I recommend you to buy Morgan Jones Valve Amplifiers, 3rd edition, available at Amazon. It is a very well written book, packed with schematics, theory, ideas, concepts, etc.

Commercial disclaimer: (Unfortunately) I am not related to him

Erik

[cbutterworth]

Erik,

Great! I will download/print the article and try to get hold of a copy of the book that you recommend.

I had read before that it is best to use a Constant Current in PSUDII. Now, the specs for the 12B4A state: "plate current = 9.6mA" for Class A amplifier. So for a stereo from a common PSU (ie. two tubes from a single PSU), I would simply use 9.6 X 2 mA for my constant current load????

However, there is a second column of numbers, which states: 34mA for plat current.

OK, a second datasheet states: plate current for grid voltage of -23V = 9.6 mA. But it also states Plate current of 34mA elsewhere.

Hmmmm....maybe the lightbulb is just switching on here. Is this where I use the charts to look up grid voltage and corresponding current-draw???

Given that tubes seem less exacting than other types of components, maybe all the numbers do not need to be exact, but rather within design tolerances.

Thanks,
Charlie

[Original Burnedfingers]

Charlie,

I hate to be the one to talk negative here but there are far better line stages to build than this one from the diy paradise site. To be perfectly honest it doesn't sound all that good. I built both of the line stages from the paradise site. It sounds ok as does the 5687 but that's about it.

I would highly suggest building an Aikido line stage. It will cost about the same amount of money when you figure you won't need the chokes with the Aikido. Also, a plus here is that all the power supply design work has been done. There are pages of information on the construction of the Aikido here.

[cbutterworth]

I have looked at the Aikido. It certainly seems that folk really like it.

Still, the artcicle by John Broskie doesn't include a PSU. The posts in the forum seem pretty mixed with regards to recommendations about the PSU - some are very complex.

Of course, I would still have to decide what kind of tubes to use. I know that you suggested the 6FQ7 and the 5687, although I would prefer less gain. I would also still need a suitable transformer, and would this be followed by some kind of rectifier / filter?

I have found the printed circuit boards for sale. Would point-to-point be better sounding?

As always, questions, questions, questions......I really am a newbie at this

Charlie

[Original Burnedfingers]

Charlie,

If I may... I built a 6sn7/6sn7 Aikido hand wired. I've also built the Aikido's using the Diyaudio boards and John Broskie's board.
The Aikido is a superior sounding line stage.

There are numerous pages that would show different tubes and the gain. There are people on this forum like SY that enjoy helping/teaching others. The power supply will not be a problem.

Go for the stars and pick a combo that will give you the gain you want and then ask for help. You will receive it.

I'm not saying the 12B4 line stage is bad. Heck I have one sitting on my shelf in the garage. I will tell you that for the money invested you will be further ahead with the Aikido. I have a number of line stages sitting on my shelves. There are others that would enjoy making only one good line stage.

I would suggest going thru all of the Aikido threads and taking notes or printing them off. Do the research and make up your mind before going further.

I would be interested in knowing what you have for speakers and amplification.

[Sheldon]

Originally posted by cbutterworth
Erik,

Great! I will download/print the article and try to get hold of a copy of the book that you recommend.

I had read before that it is best to use a Constant Current in PSUDII. Now, the specs for the 12B4A state: "plate current = 9.6mA" for Class A amplifier. So for a stereo from a common PSU (ie. two tubes from a single PSU), I would simply use 9.6 X 2 mA for my constant current load????

However, there is a second column of numbers, which states: 34mA for plat current.

OK, a second datasheet states: plate current for grid voltage of -23V = 9.6 mA. But it also states Plate current of 34mA elsewhere.

Hmmmm....maybe the lightbulb is just switching on here. Is this where I use the charts to look up grid voltage and corresponding current-draw???

Given that tubes seem less exacting than other types of components, maybe all the numbers do not need to be exact, but rather within design tolerances.

Thanks,
Charlie

Here's an article that explains the basics of setting tube operating parameters:

http://members.aol.com/sbench102/po-dis.html

Second the recommendations on Jones and Broskie. Add Steve Benchs' site to that and you've got enough source material to take you a long way (coming from a fellow neophyte).

Sheldon

[Sheldon]

Originally posted by cbutterworth
I had read before that it is best to use a Constant Current in PSUDII.

You will design your amplifier to have a specific DC operating point (plate voltage, current). Since you have to specify the voltage and current for the amp, it's easiest to just plug in the desired current as a Constant Current load in PSUD and then adjust power supply components (resistors, diodes, inductors, caps, transformer, etc.) to give you the correct voltage and desired ripple characteristics. PSUD also allows you to use the step function to check for ringing when the load changes quickly (as during large music transients).

Sheldon

[cbutterworth]

Burned Fingers,

I emailed John Broskie about the boards. Based on his reply, I have settled for 6SN7 for all four tubes (at present). He actually suggested that 12sn7's were cheaper, but I cannot find any available. He also suggested that I consider the 6DJ8 as a pair to go with two 6SN7.

So, I have pondered the power supply, and will go with around 220V using a Hammond 272BX 250-0-250 going into a 5U4GB, going into two 12H 155 ohm chokes, using 50uF caps.

I'll post the schematic and see what comments I get for the PSU, such as whether, I would really need two chokes, etc.

For my other equipment, I have an AKSA 55N amplifier (www.aksaonline.com); Polk rt600i speakers; and a new Rega Apollo CD-player. Currently, I am using a homebrew passive preamp with Elma source selector and 50K Alps pot in shunt mode.

My next big upgrade will be speakers, as the Polks are definately the weak link in the system. I may buy new speakers such as Vandersteens, or build my own (GR-Research, Selah, etc.).

When I build the Aikido, I'll install and new 100K stepped volume control, either from Glassware Audio Design, or somewhere else.

Anyway, I'd appreciate you ideas.

Charlie

[hihopes]

A friend of mine has built a number of tube line amps, some his own designs and some other peoples. The most disappointing one he has tried was a 12B4A. He has 2 Aikidos - one hardwired and one with a board. They are both stunning - in a class of their own - but there is no question that hardwired one sounds a bit better. He is using 6N1P for 1st stage and 5687 for second. Hope this helps.
William.