Vacuum Tube Amplifiers

Tube amp project support

Vacuum Tube Amplifiers

Tube amp project support

Vacuum Tube Amplifier Basics

Vacuum Tube Amplifier Basics
EJ Jurich

There is a growing number of audio enthusiasts and hobbyist interested in creating their own vacuum tube amplifiers. If one has the necessary technical information, high quality tube amplifiers can be assembled using point-to-point hand wiring.

For the novice not versed in electronics several sections of the book cover electronic basics. Includes how capacitors work, voltage, current, ohms law, reading circuit drawings plus other related information.

Principles of vacuum tube operation includes function of grids, effect of tube capacitance, tube resistance, heat dissipation and voltage gain. A table of component values for the popular 12AX7 in various operating parameters simplifies pre-amplifier stage design. Power supply sections cover vacuum tube and solid state rectifier conversion of AC to DC and DC filtering. A sample power supply is used to explain calculating loads, determining required transformer ratings and component values. Includes high voltage, bias and filament supplies.
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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 into an AC outlet, circuit grounds might actually be on the hot AC main.
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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.
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Vacuum Tube Gain Controlled Amplifier

Vacuum tube audio processor for maintaining an average level while preserving dynamics using an all triode vacuum tube design built around the 12AX7 dual triode. This is the gain controlled amplifier mentioned in The Allure of Vacuum Tube Amplifiers.

A gain controlled amplifier (also called a compressor) is an amplifier that maintains an average output level over a larger input level range. This type of amplifier is used to prevent over-driving audio systems and keep levels in a more comfortable listening range.
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Importance of Filament Voltage

Tubes have an optimal filament voltage, most common is 6.3 volts. Although a voltage range below and above the optimal voltage is specified in datasheets there is good reason to not apply more than the optimal value.
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Amplifier Power
Sound Pressure Levels
Saving Money

Building a vacuum tube amplifier can be expensive, transformers and power output tubes can be especially pricey. If you are working with a tight budget, there are options available to help reduce costs. Backing off on amplifier power and referring to sound pressure levels for loudness can save you money and save your hearing.
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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.

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

6L6G 6L6GC

From Chelmer Valve in Great Britain provides data over a wide range of operating voltages. Use in conjunction with current manufacturers datasheet.  Chelmer still exists, but no longer handles audio vacuum tubes.

6L6G 6L6GC Datasheet 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 exercise 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.

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