nicovlogg wrote
Kind of a tangent question, but thought you might know - why are the power tubes heated by AC current (the rectifier supplies only to the pre-amp tube heaters) Doesn't AC current cause noise when used for heaters?
The rectification of preamp tube heaters is not a general thing, your amp might have it but others don't even.
The amp designer tries to cancel the hum by referencing both sides of the heater to ground through an identical resistor (it needs referencing since it otherwise would run up to some high voltage and then arc to the cathode). You could rectify (a number of hifi amps use this method) but you are likely to rectify solid state because of the low voltage. In the golden age of the tube amp there were none of those lovely 1N4007 and one would need to go through a whole lot of trouble to rectify. In the very very early days (before electric guitars were even invented) heaters would be fed with batteries, hence the 5-6.3-12.6 voltages we still see. To cut a long story short, since the sixties we know that a guitar amp can be almost hum-free on AC heaters and we accept the sound of sixties amps as our reference now. The remainder of the hum is generally considered 'good hum', it lets you know you are switched on. 8)
