Patrick Turner wrote:

Ian Thompson-Bell wrote:
I am designing a tube based microphone pre-amplifier. At present I am
trying to sort out the HT supply topology. I would prefer a simple RC
network but this reduces the anode volts available to the first stage. I
want to avoid 'anode starvation' and it attendant colouration so my
question is below what voltage would the anode be considered to be
'starved'? The preamp uses 6AU6 tubes.

Cheers

ian

There is nothing wrong with CRCRCRC type filters for preamps.

You need forst to abandon completely trying to copy
what was done in 1955 where preamps rarely had more than 47uF caps.
For good filtering, R had to be high, and thus you got a dc voltage drop
you didn't
want.
AND you also got a preamp very likely to oscilate at LF, ie, motorboat,
because it is a de-facto phase shift oscillator.

But these problems dissapear if you use LARGE value capacitors
which are now quite cheap, such as 470uF x 450V rated.

Patrick, I notice you use these in a number of designs featured on your
web site. Where to you get yours form?

Cheers

Ian