On Sun, 25 Nov 2007 01:44:55 GMT, Patrick Turner
wrote:

How true, but I have designed semiconductor audio stuff for years
(actually decades). Now I want to design/build some (pure) tube gear.

Filtering is just as important in SS circuits....

Patrick Turner.

No it isn't. SS circuits are generally built fully balanced, using
current sources instead of collector load resistors etc, which gives
them many dBs more common mode and power supply rejection than you see
in a valve circuit. You can get away with much poorer supply filtering
in SS.

Now as for valves, don't just slap in big capacitors; think. This is a
filter you are designing, for a specific purpose. So design it. Decide
how many dB rejection you need at 100 (120) Hz and do the sums. That
will give you a set of resistor and capacitor values you can use as
your minimums, Check that the spec is still met when you include the
parasitics of internal resistance in a cap; there is no point trying
to cure hum by making a cap bigger when it is the ESR causing the poor
performance.

d

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Pearce Consulting
http://www.pearce.uk.com