Paul Joppa
Moderator
Just thought I's mention, it's the plate choke as well. Stock is about 30 henries, or 3.75 henries per kOhm of output transformer impedance. The Stereomour iron will be 35 or 40 henries - nearly 5.0 H/k. The MQ choke is 50H, 6.25H/k.
The Speco is an interesting study in what you can get. At saturation the maximum inductance is achieved, which is about 100 henries. This happens at 40Hz, 2 watts (30 Hz 1 watt, 20Hz 0.5 watt). At 1v out (1/8 watt) inductance is still quite large, 30-50 henries, and bass is extended to -3dB at 27Hz. At small signals its inductance is around 10 henries and the bass extension suffers. So it has pretty good bass at moderate levels with most of the music, with some loss of bass at very small signals and some distortion of the deep bass when near saturation.
My limited measurements indicate the Speco is built on ordinary silicon steel. The MQ is not only larger, it uses grain-oriented silicon steel and should be good for at least another octave of bass before saturation, with no significant falloff for small signal levels.
The Speco is an interesting study in what you can get. At saturation the maximum inductance is achieved, which is about 100 henries. This happens at 40Hz, 2 watts (30 Hz 1 watt, 20Hz 0.5 watt). At 1v out (1/8 watt) inductance is still quite large, 30-50 henries, and bass is extended to -3dB at 27Hz. At small signals its inductance is around 10 henries and the bass extension suffers. So it has pretty good bass at moderate levels with most of the music, with some loss of bass at very small signals and some distortion of the deep bass when near saturation.
My limited measurements indicate the Speco is built on ordinary silicon steel. The MQ is not only larger, it uses grain-oriented silicon steel and should be good for at least another octave of bass before saturation, with no significant falloff for small signal levels.
