Designing and Building
Audio Amplifiers.

50 Watt Per Channel EL34 Ultra Linear Amplifier.

Special Notice.
After putting the amplifier into operation I found a
few changes were necessary to the power supply. These changes appear in red
so you won't have to read through the entire text searching for them. These
are what a manufacturer calls post production changes. Believe me, it
happens frequently.

All photographs were taken immediately upon completion of the project.
The photo of the power supply will show 5 zener diodes instead of 4.
Neatness fell by the wayside as these post production changes were made.
Also I have used a little touch-up paint on the scratches on the output
transformers.

Doing it the right way.

IT SOUNDS TERRIFIC.

On other pages of
this site I have talked about designing amplifiers the
right versus the wrong way. This one was definitely designed the right
way. I spent several months and more than a little money finding the best
output transformer. Then I investigated various output tube types and
configurations. Some I didn't write up and post. Then I spent many days
looking into various phase inverter and driver configurations, again many I
didn't post. This amplifier circuit has distortion of less than 1 percent
before the global feed back is applied. When the feedback is connected the
distortion almost becomes too small to measure with the equipment I have.

In the breadboarded version of the amplifier the figures came out exactly
as reported on the Ultra
Linear Monoblock page.

General.
Although you may think of a quartet of EL34s as overkill it
was the only way I could get the low distortion figures I wanted. Frankly I
don't see how some manufacturers of commercial gear got what they claimed
back in the 60s. Maybe they didn't and were just claming they did. But
that's a discussion for another page.

This circuit appears to many people to be a Williamson. The first
amplifier stage is not directly coupled to the split load phase inverter but
that appears to be the only difference. The phase splitter is followed by
an amplifier and the output tubes are operating well below maximum power.
Also, I have used high mu triodes instead of the low mu ones used in the
original Williamson circuit. This permits the use of a lot of cathode
degeneration which reduces distortion to a very low level.

I have broken up the article into several pages because of the size of
some of the graphics files. The links below will permit you to navigate
around only seeing what you want to.

Introduction. (You are here.)

Power
Supply Schematic and Circuit Description.

Amplifier
Schematic and Circuit Description.

Power
supply chassis layout.

Amplifier
chassis layout.

Initial
tests and adjustments.

A foolish man dreams of wealth,
a wealthy man dreams of
wisdom,
and a wise man dreams of tubes aglow all in a
row.

Amplifier
Smorgasbord.

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This page last updated April 16, 2006.