May 23, 2020•405 words
So, I've just discovered that some of the more silly1 Hi-Fi people use valve2 amplifiers with valve rectifiers, because they are, apparently higher fidelity. I have no problem with valve stereo amplifiers – I own two, one of which I made – although I would hesitate to call them 'high fidelity': they sound wonderful, but so do records (records played through valve amplifiers sound even better), but they both sound wonderful because they have significant distortion. 'That warm sound' ... is distortion. But valve rectifiers in amplifiers which claim high fidelity are a joke, in two ways.
Firstly the only reason you can still buy rectifier valves is because some guitar amps use them. In fact, probably the only reason you can still buy any audio valves at all is the same. Of course the golden eared are not aware of this because they live in a world only tangentially related to this one, an invented world with an invented past.
Secondly, why do some valve guitar amps still use valve rectifiers? Solid state rectifiers have been available for a very long time: the very famous Marshall 1959 'plexi' from 1965 had a solid state rectifier, for instance. So why do some guitar amps still use valve rectifiers? The answer is that valve rectifiers have a rather high internal impedance, and this means that under heavy load they suffer from what's called 'sag': the output voltage of the rectifier drops or, well, sags. This in turn means that the power valves in the amp, particularly, see lower plate voltages, and (since the amp is already being driven hard) this causes more distortion. This is a desirable characteristic for a guitar amp as it means the amp becomes very responsive to playing dynamics: play a note harder and there is more sag & hence more distortion. And guitar amps mostly exist to add distortion of various kinds to the sound of the instrument.
So, wait: valve rectifiers still exist because they sag under load, and sag dramatically increases distortion from the amp, and makes that distortion depend in complicated ways on programme level. So, if you wanted high fidelity, well you wouldn't be using a valve amplifier in the first place, but you definitely wouldn't be using one with a valve rectifier. Oh.
It's hard to find words for the level of stupid here.