On Wed, 10 Jul 2013 12:55:38 +0100, "Arfa Daily"
wrote:



"Phil Allison" wrote in message
...

"Arfa Daily"

The power supplies in guitar tube amps are universally linear. Simple
transformer, full wave rectifier, reservoir cap followed by L-C or R-C
filtering. Rails up to 500v can typically be found feeding the output
stage, and it's not at all unusual to see ripple voltages of 5 volts or
more on these high voltage rails.

** The ripple voltage on the first filter electro is typically 10% of the
DC level - at ful load.

This means up to 50V p-p for a 500V rail.


The hum on the output is barely noticeable,

** The push-pull output stage rejects supply hum almost completely - until
the amp goes into clipping.

However, it is crucial that the screen supply is hum free or the output
will be amplitude modulated at 100 Hz.

Fender made a blunder with this when they built the Super Twin.


... Phil


Yes, all agreed, and of course the reason that the early stages *do* have to
have a smooth anode supply is that they are single ended, unlike the output
stage.

Arfa

Yes that is part of it, as well as the fact that there is
amplification of the early stage hum.

peter