Why are valve rectifiers getting so popular?
With the advent of very cheap silicon diodes valve rectifiers were considered obsolete technology and by the late 1980s no major guitar amp manufacturer was using them. Four silicon diodes for use in the bridge rectifier of a guitar amp cost less than fifty pence, whereas the popular GZ34 valve rectifier typically costs at least £10. Besides cost, valve rectifiers have several other disadvantages when compared to silicon diodes: they are relatively fragile; have a finite life; they require a separate tap on the power transformer to power their filaments adding further cost; and their filaments generate heat which has to be dissipated, for example a GZ34 generates 10 W of heat just to power the filament! They also have relatively high internal impedance, which can be seen as either an advantage or a disadvantage. If you want maximum power from your amplifier, and this seems to be an obsession in the sales departments of many manufacturers, then you want a low impedance power supply. How
