Subscribe or unsubscribe our Mailing List
© COPYRIGHT NOTICE  All Rights Reserved

Last Update: 12/25/2017

OTL schematic
The rumour that Julius's ashes are in this pot are not true.

Posthum award for Julius Futterman by AES 1981

The Julius Futterman Story
The man who invented the OTL

When thinking about amplifier topology, there is
SE = Single Ended
PP = Push Pull and
OTL = Output Transformer Less Amplifer

When talking about amplifier design, this is probably the most outstanding achievement ever.

This article is about Julius Futterman, who spend his entire life on inventing and improving just one circuit: The OTL amplifier.

The Holy Grail of small signal tubes, ECC803S NOS TFK <>

About how the recipe got lost.

Read more about it here.

Help! My amplifier has a crack noise

This is an interesting picture from a VAIC reference amplifier. It had a crackling tube noise, which was socket related. Remove the tube, sometimes helped, but the noise would come back. What we found was a mosquito, catched between the anode pin and grid pin. The voltage difference is +600Volt DC. So locally, the static electric field is very high, and it attracts light weighted objects like dust pieces, a thin hair, or like here... a Mosquito! As you can see, for the poor animal the electrostatic force was so high, it stretched his legs, and then got dried in this position. Obviously the 600Volts was not enough to burn the Mosquito, it was fully intact. Yet also crackling current through the mosquito in the range of (say) 50nA will give a signal of 50mV, when the grid resistor of the 300B is 1 Mega Ohm. After amplification by the 300B you get 200mV at the tube anode.

The output transformer transforms down 1:20 so reduces that to 10mV at the speaker outputs. The human hearing limit for a crack noise is below 1mV at the speaker outputs.

You can imagine what happens if insects find their way into the 300B socket. So the part on the tube itself. That would give a crackling tube also.

Full Size image

Game Over.

This is about the famous EI tube factory. Unfortunately most of the equipment was scrapped recently. This was a shameful destruction of an intact tube factory, only recently.

Read more about it here.


You have a good tube tester, but it can not measure dynamic parameters, like Gm, Gain, or Rp? Well most of the time you can, but you need to make a differential measurement.

Instead of having to explain this just use this little Excel Worksheet. You can select the tube you want, or enter the data by hand in the right table.

Then you need to do Measurement 1 + 2 and you have the Transconductance. (Gm). If you also do Measurement 3 + 4 you get in addition the Gain the the Plate impedance.

Even so, you can use this program to check the performance of a tester, that is able to test Gm or even Rp and Gain. And no, this sheet makes no errors. Any differences are caused by the tester itself, since there are analog circuits also in digital testers, and even digital, you have the problem of low resolution if cheap A/D converters are chosen, such as in the AT1000. DOWNLOAD HERE.

About the first single plate 2A3 re-issue ever since 1950.

More information here.

A mysterious "constant current user" inside the vacuum tube heater,
or why voltage specified heaters should be voltage driven.
By Jac van de Walle

More information here

You changed good ECC88 for new ones, and the new ones are BAD. They give a loud crack noise sometimes. You are ANGRY, about the new tubes. Read here about what very probably causes the problem.

Help, I have a loud CRACK noise with my ECC88

There are some crazy methods to connect tubes, not from the
schoolbook. For instance, take a triode, and use the plate as control grid, and the grid becomes the plate. Oh, yes it DOES work! And no, the grid dissipation is not too low. I found a 300B can take a few Watt grid dissipation. I took curves, and they are amazingly nice. This gives a totally different, new kind of tube, and it is a low gain, VERY low distortion tube. Lower distortion than a normal 300B.

I have also found an article on grounding the plate of a pentode, to get a triode. (VERY low noise).

Also, you can use the Screen grid of a pentode as signal input. The control grid G1 is only used to set the bias voltage.

Stephany Bench Theory on inverted operation
Stephany Bench' method for an inverted 6080 tube
Stephany Bench. Project of inverted amplifier
Here is a grounded Plate article

Recommended wire color scheme, and same small hints about grounding

More here

What are "JAN" TESTED tubes?

About destructive Testing

CRYO TUBES and WRONG tube coolers

Why tube coolers damage tubes.

Why tubes should not be cryogenic treated!

When some passionate HiFi nuts are telling you, how they discovered break through things, doing it better than three generations electron tube builders before us, you have two options:

1) They are no nuts, and three generations of tube specialists were wrong.

2) They are nuts, and three genet rations of tube specialists were right.

Read the rest here

Nice original article by the Tungsram company about how it all began

It is in Hungarian + English language

Read article here

 Made in Japan?  No sir! 

Read more about Lynn Olson's works

What can you do with just one Watt of output power?
Read the article
Explanation of the Telefunken method of naming RE-series tubes.
Some notes about  TESLA and JJ

How a vacuum tube works,  by Eric Barbour 

Read the article

The "Loop Distortion" 

An overview of amplifier topologies, by Lynn Olson 
Technical Editor of Vacuum Tube 
Valley magazine. 

This presentation says a lot in a small space, and could easily be the subject of an entire book. This is a MUST read for every engineer. 

Read the article

The blue glow pages
5881, A new beam power tube.
By C.E. Atkins 

Commercial Engineer Tung-Sol Lamps Works, Inc. 
     Radio & Television News, September 1950. 
Read this almost 70 ears old article

An application of the AV2A3

A detailed article by M. Feretti, about how to use the 2A3 tube. 

Marco is a student of electronic engineering at the Turin Polytechnic in Italy.  He became involved with tube amplification in highschool, and then was attracted to audio  reproduction. After practicing with push-pull amplifiers, he focused his research on single ended designs. 

Read the article

How a vacuum tube works, by Eric Barbour.
At that time application engineer at SVETLANA Russia.

Very nice article, also small information about Svetlana

Dieter's violins in the City Museum of Innsbruck, Austria

The Character of Sound.
by Dieter Ennemoser. 

Dieter Ennemoser is a studied violin builder, and a great personality. I visited him, outside Innsbruck, in the smallest house, you have ever seen. Below his house is the workshop, which is so small it gets a bit crowded in there with two people. At the other side of the street is a tourist hotel, so that was only a short walk over there.

He manages his life in such a way he can do the things he likes. He sais, the reward for hard work is only the tax office treats you like a criminal. I can only confirm Dieter is right. They bite the hand that feeds them. So Dieter choose live less wealthy and more happy. He can work with violins, build them, and guide young musicians, and on his door bell is a note for the tax office, saying they have to go away. (This is not a joke) .

Dieter is the creator of the C37 glass shape, for AVVT tubes, and he is the patent owner for the word "C37" as well. When building violins, what you expect is not always what you get. It a never ending search for materials, special paint, treatments, and what is the mystery that makes a violin sound as it does.

Why do some materials sound good and other sound bad? For Dieter is has to do with biology of the materials. Violins are made from materials that were alive. Mainly wood, but not just that. Also his paint is natural. Not to forget horsehair for the violin's bow, or strings made from guts. Traditional wood glue, made of horse bones. Etc. What do all biological materials have in common? They hold Carbon molecules, and many are grown at 37°C. He called the effect "C37".

Dieter also wrote a book. He wrote it prison. His crime? Building blue violins! What exactly did he do? He used an historical colorant for his violins, and over that comes his own C37 paint. So far so good, and if you wanted one of those, you have to register on the waiting list. But here comes the problem: By law in Austria, violins must be brown. So the word "violin" is protected, and they have to be brown. Period.

However Dieter's colorant was not selected to comply with laws, but to sound best. The colorant is gray with a blue shade. Dieter was in the news, for the magnificent sound of his violins, and famous musicians payed prices, that created a lot of envie, by the organized violin builders guild. So he was under pressure to stop building blue violins. He refused until the bitter end, and to make a long story short, he was send to prison, together with other criminals.

Just FYI, here is a picture of the inside of the violins, very interesting how he does that.

Dieter is getting older now. Please support and reward him by ordering his book. It is easy to read, and most all very interesting! About the harmony between shape and materials,  and why he thinks materials sounds as they do.

German + English Version  is available from:  "Musikverlag PAN" - Switzerland.  Fax Nr. 0041-1-3114108

Subscribe or unsubscribe our Mailing List
© COPYRIGHT NOTICE  All Rights Reserved