just completed the SSE build
Parts
- PT: Hammond 6k7vg
- Choke: Hammond 193J
- OPT: Hammond 1628SEA
- 5AR4
- EL34
- 12AT7
Readings:
- B+: 450v (with tubes with no load)
- Plate current: 62.5mv
Input 2v 1K signal
positive peak: ~9v
negative peak: ~-10v and start clipping
it sounds great, but just want to understand what causes the asymmetrical sin wave.
thanks
Parts
- PT: Hammond 6k7vg
- Choke: Hammond 193J
- OPT: Hammond 1628SEA
- 5AR4
- EL34
- 12AT7
Readings:
- B+: 450v (with tubes with no load)
- Plate current: 62.5mv
Input 2v 1K signal
positive peak: ~9v
negative peak: ~-10v and start clipping
it sounds great, but just want to understand what causes the asymmetrical sin wave.
thanks
Asymmetrical clipping in an SE amplifier (or any amplifier fort that matter) is due to the characteristic curves of the output tube.
look at the spacing of the grid voltage with respect to plate voltage. Along any fixed current line (horizontal) the spacing varies and compresses at the extremes.
The change in current for a given change in grid voltage is not linear. It compresses in an unequal way. This results in an uneven distortion of the waveformwhich produces second harmonic distortion products. Equal distortion produces odd harmonic components.
look at the spacing of the grid voltage with respect to plate voltage. Along any fixed current line (horizontal) the spacing varies and compresses at the extremes.
The change in current for a given change in grid voltage is not linear. It compresses in an unequal way. This results in an uneven distortion of the waveformwhich produces second harmonic distortion products. Equal distortion produces odd harmonic components.
It is true that asymmetrical clipping is part of an SE amp's nature. Sometimes it can be tweaked closer to symmetrical by adjusting the operating conditions (bias and load) on the tubes.
There is not much we can do to change the load, but the bias points for both the driver and output tubes can be adjusted by experimenting with the cathode resistor.
The driver tube operates well below its clipping point, so any clipping seen is likely from the output tube.
It is often the case with the output tube that the point of symmetrical clipping lies in a range of current that's too much for the tube, and a trade off between clipping performance and tube life must be made.
There is not much we can do to change the load, but the bias points for both the driver and output tubes can be adjusted by experimenting with the cathode resistor.
The driver tube operates well below its clipping point, so any clipping seen is likely from the output tube.
It is often the case with the output tube that the point of symmetrical clipping lies in a range of current that's too much for the tube, and a trade off between clipping performance and tube life must be made.
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