Stereo 20  
Long-Tailed-Pair Distortion
(LTP driven direct from oscillator, output into 242kOhm load)
Some power supply filtering added to minimise PSU hum & noise.
ECC83, Phillips Miniwatt, Dual Triode
Output THD and Noise, %
Volt-peak, into 242kOhm Triode Section #1 Triode Section #2
2 Vpeak - -
5 Vpeak 0.05% 0.05%
11 Vpeak (=9 Watts Output) 0.12% 0.12%
20 Vpeak 0.45% 0.40%
30 Vpeak 1.00% 1.00%
40 Vpeak 1.90% 1.90%
ECC83, AWV Radiotron, Dual Triode
Output THD and Noise, %
Volt-peak, into 242kOhm Triode Section #1 Triode Section #2
2 Vpeak - -
5 Vpeak 0.05% 0.05%
11 Vpeak (=9Watts Output) 0.12% 0.11%
20 Vpeak 0.38% 0.38%
30 Vpeak 0.95% 0.95%
40 Vpeak 1.90% 1.90%
Stereo 20, Overall Distortion
LTP driven from oscillator, output into 15 Ohm resistive load
Left Channel THD and Noise, %
NEC 6BQ5's
9 Watts Average, Open Loop 0.80% Corresponds to 11 Volts-peak output from driver
9 Watts Average, Closed Loop 0.05%
Right Channel THD and Noise, %
AWA Radiotron 6BQ5's
9 Watts Average, Open Loop 1.30% Corresponds to 11 Volts-peak output from driver
9 Watts Average, Closed Loop 0.11%
TL/10  
Long-Tailed-Pair Distortion
(LTP driven direct from oscillator, output into 242kOhm load)
Some power supply filtering added to minimise PSU hum & noise.
6SN7, Super Radiotron (Aust), Dual Triode
Output THD and Noise, %
Volt-peak, into 242kOhm Triode Section #1 Triode Section #2
5 Vpeak 0.07% 0.10%
10 Vpeak 0.08% 0.15%
20 Vpeak 0.16% 0.30%
6SN7, RCA (USA), Dual Triode
Output THD and Noise, %
Volt-peak, into 242kOhm Triode Section #1 Triode Section #2
5 Vpeak 0.15% 0.12%
10 Vpeak 0.22% 0.17%
20 Vpeak 0.35% 0.50%
TL/12  
Long-Tailed-Pair Distortion
(LTP driven direct from oscillator, output into 242kOhm load)
Heavy power supply filtering added to minimise PSU hum & noise.
6SN7-GTA, Super Radiotron (Aust.), Dual Triode
Output THD and Noise, %
Volt-peak, into 242kOhm Triode Section #1 Triode Section #2
10 Vpeak 0.10% -
20 Vpeak 0.14% -
30 Vpeak 0.15% -
35 Vpeak (=approx 10 Watts) 0.17% -
6SN7-GT, RCA (USA), Dual Triode
Output THD and Noise, %
Volt-peak, into 242kOhm Triode Section #1 Triode Section #2
5 Vpeak 0.10% -
10 Vpeak 0.12% -
20 Vpeak 0.16% -
30 Vpeak 0.22% -
35 Vpeak (=approx 10 Watts) 0.32% -
50 Vpeak 0.40% -
TL/12 Output Stage and Driver/Input-Stage Distortion
Complete amp (EF37A, 6SN7, 2xKT66) measured, output into 15 Ohm resistive load
Power Out THD and Noise, %
12 Watts Average, Open Loop 1.50%
12 Watts Average, Closed Loop 0.10%
* All THD measurements at 1kHz, and filtered below 250Hz to reject power supply ripple.
S.Spicer, May 2002.