05-11-2016, 12:12 PM
(05-11-2016, 11:37 AM)Mark Hennessy. Wrote: We assume that audio signals are symmetrical either side of ground (largely true, but there are some exceptions). Therefore, we bias in the centre of the available voltage range, which means that when clipping occurs, it'll hopefully be pretty symmetrical.
Not quite.
You bias the valve so that it's sitting in the middle of the available CURRENT range, so that when clipping occurs it's hopefully symmetrical (like you said). Then, you check that the bias you need is at least equal to the peak input swing, so that the grid never has to try to go positive (if it does, you get a new distortion mechanism).
If this isn't satisfied, you have to operate at a lower standing current, or raise the HT voltage (so you can then increase the bias to throttle back to your favoured current). And that's why valves need high voltages!
