the new SV572-3 Single Ended Amplifier

by Andrea Ciuffoli - 2004

Design of the output stage

The starting point has been the simulations made with SE CAD 1.01 from http://www.tubecad.com/
with these targets:

• get the max power from a single Svetlana SV572-3
• with no more than 900V
• always in class A1 so never in positive grid area
• normal idle condition to have a long tube life time
• Zout less than 2 ohm to drive any loudspeakers with good damping factor so good bass frequency

In this conditions

the result will be the following:

As output transformer has been choiced the Lundahl  LL1620/90mA with secondaries connected in B configuration to have a primary load impedence of 11.5K on 8ohm load.
The LL1620/90mA have a primary inductance of 40H and the Svetlana SV572-3 have an nominal plate resistance of 1900ohm so the low frequency cut-off will be egual to Ra / ( 2 * pi * 40) = 7.5Hz.

Is also possible change the SV572-3 with an 845 tube and get a result very similar.

Design of driver/input stage

So now what I need is only a good driver stage able to give an output about 160V / 1.41 =113 Vrms with low distortion.

Follows my first test with a section of 12AX7 and an EL84 in triode confiiguration (G2 connected to Plate)..

Here the relative measurement made with Clio system by Audiomatica

The voltage is the half of the total output voltage get on secondariers of  LL1671 and thd about 0.8%.

The result is good but I would like to try to get a better result.
 
 

Follows the second test circuit with two section paralleled of an 12AX7 followed by an EL34 in triode configuration

Here the relative measurement made with Clio system by Audiomatica

N.B. The voltage in the previous image is the half of the total output voltage get on secondariers of  LL1671 and thd about 0.37%.

N.B. The voltage in the previous image is the half of the total output voltage get on secondariers of  LL1671 and thd about 0.22%.

now the result is very good

continue soon ....................