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.
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.
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.
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.
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.
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.
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.
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.
ejjurich.com 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.
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