Vacuum Tube Amplifiers

"they sound good and keep you warm at night"

A Brief Bio of EJ Jurich
EJ Jurich

Originally From Chicago
Current Age -
Radio Broadcast Engineer, retired

Started tinkering with electronics in 1955 at the age of ten. I had a table in my room where I started experimenting with tube amplifiers. The tubes I used were 35W4 rectifier, 12AX7 and 50C5 output tubes. These were mostly tubes used in AC/DC radios of the time. Filaments were wired in series and connected directly across the 115VAC power main. The 35W4 rectified AC directly from the 115VAC power main, there was no power transformer. This would mean working with a chassis where ground circuits connected directly to the AC power main. AC plug prongs were the same size allowing a plug to be plugged into an AC outlet either way. Depending which way the amplifier was plugged in circuit grounds might actually be on the hot AC main.

Sound dangerous? Yes and I got my share of shocks. I learned really fast how to safely work with high voltage circuits. The AC/DC concept was a throwback to an earlier time when some parts of a city might have DC power. It was not a good concept for high quality audio. To prevent dead shorts across the AC main, circuit grounds to the chassis and input/output connections were through a capacitor bridged with a high resistance of around 220K ohms to limit current. This created some hellacious ground loops requiring AC plugs to be reversed. Even then ground loops would haunt.

Around twelve years old my father bought me a Space Spanner Knight Kit. He wanted me to experience a radio with a regenerative detector like he had when he was young. I built a few more Knight Kits and continued coming up with audio circuits of my own. My favoriate home built project from around 1964 was a stereo amplifier using push-pull 6CA4 output tubes. About the same time Knight Kit came out with a new soild state amplifier kit claiming great specs for the time including virtually no hum. I decided to build one of these new high-tech amplifiers. I took a trip down to Allied Radio on Western Avenue and bought one.

Knight Kit Solid State Amplifier Kit

After a couple days of wiring the kit together, I connected the amplifier to my system and powered it up. The first thing I noticed was a significant hum when the volume was turned up. In fact, a much higher hum than my 6CA7 amplifier. The wiring was rechecked and was correct. Some of the audio wiring was unshielded so I tried to reposition wires, but made no difference. I decided the hum was below normal listening levels and let it be. Although I did wonder what Knight Kit thought virtually no hum means.

Started playing an album on the turntable and after a couple songs I felt the amplifier sounded flat, no life to the sound. I tried several albums and results were the same. Connected my 6CA7 amp back up and the sound improved 300% (well sounded a lot better). Set the high-tech amp aside and went back to my tube amp. I've been a tube person ever since. If you read the entire Allure of Vacuum Tube Amplifiers article below you will see that the sonic difference of vacuum tubes still held true in 1990.

WROK, Rockford 1969
Me in 1969
WROK, Rockford

Denver, 2009
Me in 2009
(and wife)
Last Radio Gig

In 1969 I developed an interest in radio broadcast engineering. During the summer I studied, took the FCC tests and got my FCC First Class License. I landed my first assistant engineer job at WROK in Rockford, Illinois. A few months later I heard CBS in Chicago was looking for staff engineers. I stayed with CBS for three and half years. Then, WROK was looking for a new Chief Engineer and offered me the job. I was back in Rockford for my first Chief Engineer position. Those were fun times. WROK-AM was a high rated top-40 station still spinning 45s'. Slightly more than forty years were spent working at various radio stations around the country as Chief Engineer. Some of the cities include Milwaukee, Miami, Mobile, Baltimore, Birmingham, Grand Rapids, St. Louis and Kansas City.

After I retired, I had more time to work on tube amplifier designs. While browsing around the Internet I noticed there was not much vacuum tube information available for hobbyists. Web sites and books had material, but not at a level for hobbyist. In particular, the math was far more detailed than necessary to build a working tube amplifier. I decided to take a stab at writing a book geared towards the home electronic hobbyist. I did finish one in Kindle eBook format titled Vacuum Tube Amplifier Basics. Not being an experienced writer that first book was full of grammar errors and not well written. It did, however, sell fairly well and I was inspired to fix up the book.

The Allure of Vacuum Tube Amplifiers

There are a few possible reason for the allure of vacuum tube amplifiers. Perhaps it is nostalgic, status symbol of owning a vacuum tube amplifier or possibly because of the way audio sounds amplified through vacuum tubes. If you ask audio enthusiasts who prefer vacuum tube amplifiers, more than likely they will say it's the sound. The opinion of a few audio enthusiasts may not mean much. How about the opinion of a few thousand ordinary people. Click here to read rest of the article

6SN7 Headphone Amplifier

This is an experimental headphone amplifier using one section of a 6SN7 as the output tube. Power output at 1KHZ is ½ watt sufficient to drive headphones loud and speakers in a small room to a moderate listening level. With the tone control set in middle rotation frequency response measured 40HZ to 18KHZ -3db points.

6SN7 Amplifier

Speaker Binding Post
Speaker Binding Post
Speaker Binding Post

Gold Plated
Speaker Connect Posts
4 for $11.48

free shipping

Custom Panel Engraving
Custom Panel Engraving
Custom Panel Engraving

Single Panels
Production Runs

Tube amp transformers
Tube amp transformers
Tube Amp Transformers

Power Transformers
Output Transformers
Custom Wound Transformers
Made In U.S.A.

Vacuum Tube Amplifier Basics

Vacuum Tube Amplifier Basics
8½ X 11 Paperback
LULU Bookstore

Principles of vacuum tube operation includes function of grids, effect of tube capacitance, tube resistance, heat dissipation and voltage gain. Projects include a 30 watt monoblock amplifier designed for tube rolling.

Vacuum Tube Amplifier Basics

Vacuum Tube Amplifier Basics
PDF eBook
Secure Payment & Download

PDF is an excellent format for eBooks. They can be opened in many tablets and on a PC or laptop using Adobe Acrobat Reader.
This is the only up to date eBook version of the print book available direct from the author.

Acrosound Amplifier Circuits

These are circuits from the 1955 Acrosound transformer catalog. The circuits are updated using current available transformers, component values and have a parts list. Building using only a circuit drawing as guide requires some amplifier building experience.


6L6 Push-Pull
Center-Tap Output Transformer
6SL7 Driver/Phase Inverter


Williamson Type Circuit
Pentode or Triode Output Option
6SN7 Driver/Phase Inverter


6V6 Push-Pull
Ultra-Linear or Tetrode Option
12AX7 Driver/Phase Inverter

The Rejuvenation of Vacuum Tubes
Lane S. Upton

This is a good reference source for those who wish to try bringing weak tubes back to life. It does require the use of a tube tester.

Rejuvenation of Vacuum Tubes PDF

Secrets of Output Transformers
Menno van der Veen

A lot of good information about output transformers, amplifier performance and selecting an optimal output transformer for a special application.

Secrets of Output Transformers PDF

RoHS beware the Grim Reaper
, beware the Grim Reaper of electronics

vacuum tube amplifiers
High Voltage Audio
New to electronics or experienced, when working with vacuum tube equipment be careful where you put your hands.

DISCLAIMER assumes no responsibility for damage, injury or otherwise related to any use of information on this site or given by other means. Many electronic circuits, in particular vacuum tube circuits, operate with dangerous voltage and current. Always excercise care when working with electronic circuits.

EJ Jurich has no association with sites offering free downloads of my book. A site that offers free downloads or wants you to register beware. If the download is free, then why would they require you to register? Free download or torrent sites are notorious for passing malware on to you. Be very careful.

For those wondering what happened to the resource links at the bottom of the page. Those links needed to be verified every few weeks. In an effort to reduce web site maintenance and have more time to work on circuit design the site was reduced to primarily my own material. EJ Jurich

copyright 2014 -