300B Tube Amplifiers Parallel Push-Pull Rudolf Moers from the Netherlands has kindly sent us details of his parallel push-pull 300B monoblock tube amp

Parallel Push-Pull 300B Tube Amplifiers

Rudolf Moers from the Netherlands has kindly sent us details of his parallel push-pull 300B monoblock tube amplifiers to share with the DIY Audio community. It should be quite obvious from the photographs that the design and construction of a pair of amplifiers this size is by no means a small undertaking. Rudolf tells us that he spent about 14 months designing and constructing the pair of monoblock amplifiers. The total cost of each amplifiers was about 1300 Euro, or about $1760US as of 29 September 2010. Each monoblock weighs 25 kg (55 pounds) and the overall dimensions are 530 mm deep, 390 mm high, 400 mm wide.

Schematics - Parallel Push-Pull 300B Tube Amplifier

The few notes on the schematics are written in Dutch. You can use a free online language translation service like Google Translate to translate them into English.

• Parallel push-pull 300B vacuum tube amplifier Schematic - [PDF - 270 kB]
• Parallel push-pull 300B vacuum tube amplifier Block Diagram - [PDF - 43 kB]

Parallel Push-Pull 300B Tube Amplifier

The input stages consists of a preamplifier and cathode phase splitter using a ECC82 (12AU7), amplitude amplification (driver) using a ECC99 and cathode followers using a ECC82 (12AU7) tube. The output stage uses four 300B directly heated power triodes in a parallel push-pull configuration (Ia = 40mA and Vak = 356 VDC) with no negative feedback. The output power for each monoblock is about 25W.

When powered on the heater supply for the ECC[82,99,82] tubes goes from 1.5 to 6.3 VDC in 30 seconds. Likewise, the 300B heater supply goes from 1.5 to 5.0 VDC in 30 seconds. Polarity of 5.0 VDC heater supply can be reversed with a switch. All the heater voltages are separated using galvanic isolation.

The high voltage supply uses a mercury filled full-wave rectifier AX50 and is switched on when all heater voltage are at about 90% of their final value. The AX50 rectifier limits the maximum output power to 25W.

The enclosure is wooden and easily accessible with a hinged lid and there is plenty of interior space. The amplifier is constructed in a completely modular fashion with connectors. All the modules are built on prototyping boards.

Measurements Parallel Push-Pull 300B Tube Amplifier
Input power: 281 W(RMS) at 230V (50Hz/60Hz) mains voltage
Output power: 25 W(RMS) at 0 dB (775 mV) sine wave input signal
Efficiency: 8%

Bandwidth:
-0.1 dB at 20 Hz and 50 kHz at 25 W
-3.0 dB at 10 Hz and 100 kHz at 25 W

Distortion (THD) (distortion without hum suppression)
1.5% at 5 W and 10 Hz
4.0% at 23 W and 20 Hz
3.5% at 25 W and 50 Hz
3.5% at 25 W and 100 Hz
3.5% at 25 W and 200 Hz
3.4% at 25 W and 500 Hz
3.5% at 25 W and 1 kHz
3.5% at 25 W and 2 kHz
3.5% at 25 W and 5 kHz
3.5% at 25 W and 10 kHz
3.3% at 25 W and 20 kHz
2.7% at 25 W and 50 kHz
4.4% at 15 W and 100 kHz

THD < 1% at 2 W between 10 Hz and 20 kHz
THD < 2% at 10 W between 10 Hz and 20 kHz
THD < 3% at 15 W between 10 Hz and 20 kHz

Hum voltage over the loudspeaker is < -51 dB and inaudible with an ear against the loudspeaker.


Rudolf informs us that the design of this parallel push-pull 300B tube amplifier is explained in his new book "Fundamentele versterkertechniek met elektronenbuizen", ISBN 978-90-5381-226-6 which is currently only available in Dutch. However, an English translation "Fundamental Amplifier Techniques with Electron Tubes" is expected

READ MORE - 300B Tube Amplifiers Parallel Push-Pull Rudolf Moers from the Netherlands has kindly sent us details of his parallel push-pull 300B monoblock tube amp

Oatley K272A Head Amp audioXpress Review The December 2010 issue of audioXpress magazine includes a review of the $30AU Oatley Electronics K272A tube

Oatley K272A Head Amp audioXpress Review

The December 2010 issue of audioXpress magazine includes a review of the $30AU Oatley Electronics K272A tube based Headphone Amplifier Kit. Mark Houston completed a review of the Oatley Electronics K272 Headphone Amplifier Kit in August 2009 and since then many hobbyists have enjoyed this inexpensive audio kit. The hybrid headphone amplifier kit uses 6418 sub-miniature vacuum tubes and a headphone driver integrated circuit (PT2308). Adding appeal to the tube based kit is battery operation.

Highlights from the audioXpress Reliable Review of the Oatley Electronics K272A Headphone Amp by Aren van Waarde.

"Oatley Electronics (www.oatleyelectronics.com), which sells electronic parts and used equipment in New South Wales (Australia), has launched a small range of audio kits based on tube technology. My interest was raised by glowing reviews written by Mark Houston, ..."

"My initial impression of the sound of the K272A: warm, pleasant, and detailed. Organ music sounded great."

"... the K272A/Grado combination produced excellent sound: a fne bass (powerful and deep but not overblown), detailed mid-range, sweet top-end. Tonal colors of string instruments and vocals of male and female soloists were naturally represented. Many small, previously unnoticed details of recordings were revealed."

"In direct A/B comparisons, the K272A sounded better than the G4OEP (3/08 aX, p. 36) and even slightly better than the Stor class A amplifier (6/03 aX, p. 30)."

"For the asking price of 30 Australian dollars, the K272A is an absolute bargain. And it does not involve any dangerous voltages."

The full review of the Oatley Electronics K272A Headphone Amp is available as a direct download from audioXpress [PDF- 737kB].

Additional Oatley Electronics Audio Kit Information:

• Mark's review of the Oatley Electronics K272 Headphone Amplifier Kit.
• Tube Matching circuit in the Oatley Electronics K282 RIAA Phono Preamplifier Kit review.
• Forum thread: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272A Audio Kit).
• Forum thread: Oatley Electronics K281 6418 Tube / LM1875 IC Amplifier Kit

What's Playing: Clannad - Macalla

READ MORE - Oatley K272A Head Amp audioXpress Review The December 2010 issue of audioXpress magazine includes a review of the $30AU Oatley Electronics K272A tube

SuperCables CookBook - Review (1/2) Recently I got a chance to read the "SuperCables Cook Book" (3rd edition) by Allen Wright of Vacuum State Electron

Recently I got a chance to read the "SuperCables Cook Book" (3rd edition) by Allen Wright of Vacuum State Electronics and I thought I would share my findings. As the title implies, this is an instructional book on how to make various cables. The book covers balanced and unbalanced line level (interconnect) cables, speaker cables, mains (power) cables, digital cables and even video cables. The book is just shy of 200 pages and retails for 40 Euro and that price includes worldwide postage.

I thought of writing a book review only with no chat about the technical gems held within. That was until I finished reading the book through. I found not only some cable designs I would like to build but some confronting mathematical and theoretical proof that thin wires rule over thick wires.

SuperCables CookBook Review

The book is spiral bound, with a clear plastic front cover, black card-stock back cover and the paper quality is low. For about the same money one can purchase beautifully bound, hard cover manuals full of color photos, but let's not judge a book by it's cover. One plus about the spiral binding is the book will lay flat which makes it easy when working from a particular page. Unfortunately the image quality is poor and boring – the images look like black and white copies of color photos. You don’t find yourself looking at a picture of a good looking cable and think “I want to build that”, but don't let that discourage you. Some of the images are of such poor quality that it is hard to work out what point is being displayed.

Apart from the usual trademarks, disclaimers, copyright warnings etc. The book opens with Contents, About the Author, Introduction and A Brief History. It then works you through the theory and concepts of electricity traveling through a conductor. The book then works it way into speaker cable constructions, interconnect cables, mains cables etc. Toward the back of the book more varied cable types can be found, balanced, digital and even video cables. The list of cable types is very comprehensive. I must congratulate the author on covering such a huge range of cables.

Reading the Book
There are three ways you can go about reading the book.

1. You can read the book cover to cover;
   
2. You could skip the preface, author, intro, theory and concepts and jump right to a cable recipe. For many you can follow a recipe, construct the cable and enjoy while never looking back;
   
3. But here is my suggestion after reading the book. Read from the front cover to the theory. Jump the theory but read the concepts. Then find your first cable to build and you will likely not stop at one.

Working through the theory and maths, no matter which famous mathematician developed them, will not make you a better cable builder. However, understanding and the concepts for better cable construction and applying those concepts will. If you read nothing else prior to your mystical journey into strange cables, read the concepts section from pages 42 to 52. Other portions of the book that are must reads, Connector Basics and any of the other “Basic” sections in the book. This may be “basic” information, but it is good information that is often overlooked or forgotten.

Cable Construction Pages
There are 35 projects in the book. The project page layout is excellent. Across the top of each page is the cable project you about to start, “#7 Intimate Silver Foils” which makes it obvious what this cable is made of. The other guides on this page are: Sonics, Difficulty, Pro’s, Con’s. Some have a numerical rating other a verbal description. The next section outlines the Materials required supported by some more images. The Materials are numbered. From here we go to Method, once again numbered. At the end of the method, which is really a step-by-step list of how to put the cable together, you may find some other notes. For example, “if using Lemo’s (a brand/type of connector) and “if using RCA’s”. This layout makes it simple to follow and construct. The author also makes comments about what you may experience when listening to the cables in an attempt to rate and compared the many cable recipes in the book.

Lessons Learned
Here’s what I discovered and do agree with:

• Thin (even ultra fine) wire is better than thick wire;
• Thin foil is better than thin wire;
• Cheap light weight plugs are better sounding than extra heavy ones;
• All dielectric is bad, some not as bad as others;
• The best plug is no plug;
• Separated wires sound better than clumped;
• Solid core wire is better than stranded,
• Solder with a few percent silver or copper is good;
• The shorter the wire length the better (I think we all can agree here);
• Skin effect does occur at audio frequencies;
• Plumbers Teflon tape has more than one use;

Summary - SuperCables CookBook Review
As I stated earlier the book is very comprehensive on the subject of cables. It also highlights tricks and traps when making cables and safety issues when dealing with mains power cables. The book is well thought out, hand-holding and thought provoking. The SuperCables CookBook challenges preconceived ideas about materials used in cables, cable construction, plugs and even how a cable should look.

At around $AU60 the book is not cheap. Do I recommend the book? Yes I do. If you want a good read, buy a novel. If you are a DIY Hi-Fi nut, this book will ease your cravings. Expert or novice the book guides you through each build with the goal of producing a better sound from your system at very little cost. Just don’t tell your friends you replaced your expensive cable with a few strands of 30 AWG silver plated copper wire wrap. They’ll have you certified.

Part 2 of the SuperCables CookBook will follow in the next couple days and will cover how a couple of the cable recipes perform in my system

Mark Houston - Retro-thermionic.

READ MORE - SuperCables CookBook - Review (1/2) Recently I got a chance to read the "SuperCables Cook Book" (3rd edition) by Allen Wright of Vacuum State Electron