Saturday, June 6, 2009

Completing the Schematic

Now, lets finish off this before my new toy arrives.

Lets organize all the numbers that we had determined.

input is assume to be 1Vrms so Vp=1.414V

#additional note, normally, we will try to bias the tube at least 0.5V away from 0V grid, to prevent grid current, but in this case, the gasin of the stage is so high that before we even get close to 1V of the 0V grid, the power stage should have over loaded. so it doesn't matter.

DC state

RL=14kR 3W
Rk=86R 1W
Rg=1MR 1/4W

PS resistor = 2 x 200R 5W
PS Reservoir cap = 22uF
1st stage Filter cap = 68uf
2nd Stage Filter cap = 68uf

Friday, June 5, 2009


It has been a few years since I’d started to look for a mean to start on micro controllers stuff. PIC is the recommended chips as I was told they are cheap and abondon locally.

Bought many books and spent hundreds of hours surfing the net with no fruitful progress…. These books eventually became my best cure for insomnia… It never fail to put me to sleep in 20 minutes…

Everything which I found require me to build some thing, either a programmer or hardware to actually make the micro chip work… Its too much challenge for me… so the search continue

Found this book while wondering aimlessly in my local book store a month ago.

By Massimo Banzi, co-founder of the Arduino Project. Published by Make Magazine.

The cover cough my eye.

“Arduino” has appeared with increase frequency in my google search for how-to starter packages for electronically challenged beginner like me. I didn’t dig this AVR based board as I was looking for PIC stuff. What a mistake!

This is the only book on MCU which I finish reading in one go… and awake!

I learn what Physical Computing meant, Arduino uses C language, everything is open source, the board contain the necessary hardware to operate and plugin USB.

Arduino is “ready-to-go”, no need to know about bootloading, I/O connections, I2C, USB chip, communication chip... etc etc which I couldn't care less, so that noobies like me can get our claws right into the fun part.

There is a growing community such as
Seriously fun ppl.

and their web page is packed with great stuff such as ready made codes/programs, meaning we don't have to reinvent the wheel!

The potential application is only limited by your imagination! We can do useless thing with it such as teaching our flower to call for help when they get thirsty, lights off in the absent of occupant, control an autonomous robot, intelligent home system, track the sun, control an miniature UAV, feed the monkey, skin the fish.... all of which you can jump straight in as long as you know what make things tick, perfect toy for tinkerers.

Just placed an ordered a "clone" Arduido starter pack, (wanted to go for the real thing but they have the best shipping charges.) should arrive by next week, can't wait to blink some LED....

The Basic Circuit

I was forced to learn up Eagle to produce this circuit.

Tuesday, June 2, 2009

Tube Curves is Your Friend

Common stereotype misconceptions that tube design is for tube gurus with in-depth tube knowledge, Master Yoda-ish character and is one-with-the-force; In reality, anyone who is competent in prevent/avoid electrocution while working with high voltage and still remembers Ohm’s Law is competent enough. All you need is the data sheet. Allow me to demonstrate.

Firstly we get hold of the 6DJ8 data sheet as follows:-

You can start by determine the max and min safe work condition, gain, Rp, rp, plotting the best loadline… etc.

BUT I WON'T!! I will reserve that for your self-amusement during your dreary hours…

Use the Data Sheets recommendations and get straight to it before the irrational impulse of building a tube preamp subsides.

From the #Page 1 of the Data Sheet we have
Filament voltage, Vf = 6.3V,
Filament Current, If = 365mA
From this, we calculate the power required by th filament Pf = Vf x If = 2.3W

#Now write down this on your shopping list, “ 6V, >2x365mA (1A is common),transformer”

At the end of #page 2, "maximum rating, absolute value"
Series grid Resistor = 1 megohm max

you will find "Typical Charateristics" and the followings

Plate Voltage, Vp = 90V, This is the voltage across the anode and cathode
negative grid voltage, Vg = 1.3V, this is be the Bias Voltage
Plate Current, Ip = 15mA, with triode, Ip= Ik, cathode current

Now some maths,

Find Rk, using Ohm's Law,

Rk = Vbias/Ik = 1.3/0.015 =87 ohm #

Determine B+,
We will use Isolation Transformer, In my part of the world, main power is 230V AC,
Using Isolation Transformer with a bridge will yield,

Raw B+= Sqrt(2) x 230 = 325V,
we will filter raw B+ to 300V

VLoad = 300V - Vp - Vbias = 300V - 90V - 1.3V = 208.7V #

RLoad = VLoad/Ip = 208.7V/15mA = 13,913 ohm we can choose 15K resistor.

Well after all this hard work, I need to get my regular coffee fix.... We'll continue on the next installment

How to Sound Like Tube Guru 101

How to Sound Like Tube Guru 101

Common Cathode CC is name as such because its Cathode is connected to the Common Ground.

The CC is good at Voltage amplification, i.e., magnify signal; this is generally the strength of glassware.

It has high input impedance of easily a few hundred thousand ohms; in plain English, it is very sensitive to input signals and very easy to drive.

Fairly high output impedance, which means it is not so good at driving difficult or less sensitive loads such as Solid State Amplifiers and Loudspeakers without some neat tricks but its sufficient to drive another tube stage.

Biasing, to get the tube into operating condition, we set the DC bias or quasient state, its like getting your car on idle speed; When AC signal (yes, signal can only be AC, that includes noise signal too) is applied, its like stepping on the accelerator, and the engine will respond accordingly to how hard you step on it

There are 2 biasing methods in general, Fixed-Bias and Self-Biasing. My emphasis will be on Self Biasing as IMHO they are easier to tinker with and better sounding too.

Self Biasing means we put something (resistor, LED, Diode, Battery or Constant Current Sink) between the tube’s cathode and the ground so that it can generate the required bias voltage by themselves, hence Self Biasing.

Input signal, lets consider CD player output signal of 1Vrms, that means 2.83V peak to peak. V max of +/-1.414V.

You don’t need an input capacitor solder in your circuit as CDP already has an output cap to do the job.

Output coupling. We are going to use Capacitor coupling. This capacitor will ensure only signal voltage is delivered to the next stage. That’s all you have to know for now.

Recite the above to your pal is enough to impress your tube ignorant buddies.

Common Cathode Amplifier

Common Cathode Amplifier

Glass-tech is over a century old…. How hard can it be????

To cut short the chase, we will pay exclusively attention to triode for now. This should spare us from pages upon pages of boring tech-loaded content. Jumping straight to Common Cathode Amplifier (CC from here on), will speed up the whole process even further.

There are more then ample articles written on the basis theory in the net, spend some effort to google will reap fruitful return. I'll leave this to the readers to decide.

CC has its strength and weaknesses, but hey, it constitute vast majority of audio circuit in its plain or modified form, that speaks strength for itself.

Tinker with Tube Circuit

To begin with, my motive was learning electronics. I wasn’t looking for that illusive “Tube Sound”, as I was neither an audiophile nor interested in Hi-Fi. As the matter of fact, I don't even know what "tube Sound" meant!!

Fortunately, from my day job, I learn enough electrical safety practices to avoid electrocution. Nevertheless, it is an act of plain stupidity to take on 230V D.C. without paying due respect lethal aspect of electricity.

With help from very patient and persistent and unselfish cyberspace friends from all corners of the globe, I made leap and fold progress. Friendship sprout rapidly among like interest people. Its like I’d found my second childhood that I never had, it has been a fulfilling journey.

Today, through the journey, I'd beginning to have the ear for good sound and developed my own preference. I do my best to go for the best possible sound at least to my ears when designing and building amplifiers. It feels satisfying.