"Dave Plowman (News)" wrote in message
...
In article i,
Iain Churches wrote:

My 50W PPP tube amp has a noise floor of 80µV
that's -106dB

That's not typical.

Bear in mind that traditionally valve amps had AC heaters.
These days, by simply using DC, and biasing the heaters
above the cathode can make 10dB improvement in the
LF noise floor.

In the hey-day of valve amps, iron was cheap and large
electrolytics very very expensive. Now the reverse is the
case. When valve retifiers were used, the reservoir cap was
usually limited to 47µF. Now 470µF is often seen as the first
cap in a chain with one or more chokes of 10 or 20H.
This results in a PSU of low impedance with very
low ripple.

I can understand that it might suit the agenda of some
to try to maintain the idea that valve amps are plagued
with hum and noise:-)

Fortunately, this need not be the case.


Regards to all
Iain