On Mon, 3 Dec 2007 12:11:44 -0500, "Arny Krueger"
wrote:

"Don Pearce" wrote in message

On Mon, 03 Dec 2007 14:07:52 GMT, Patrick Turner
wrote:



Don Pearce wrote:

On Mon, 03 Dec 2007 12:41:34 +0000, Nick Gorham
wrote:

Assuming that the decoupling is done with zero ESR
caps, and there is no inductance in either the cap or
resistor, both of which will be false.

Given the assumed wonderful decoupling, maybe its
worth thinking how the switching spikes got to the
valve?

Lack of star point grounding would be my number one
candidate.

Nope. Star ground can mean many inconveniently long
leads all running to the same point.
Its OK in theory, but the OP killed the spikes with a
0.1uF across the HT sec as I suggested.
The path of noise wasn't in the 0V rail or star point.

I often don't have a star point. I often have a 0V buss
using 1.3mm thick Cu solid wire
the length of the circuit layout, maybe 150mm long.
Works fine.

Patrick Turner.

If you aren't too fussed about ultimate noise
performance, then no problem. When I was with Marconi
Instruments, we made a doppler radar speed meter for a
train and the first iteration of the board failed to read
below about thirty mph, when theory said it should have
been good down to two. We had missed star-pointing every
track around the input by about two mm. That was all it
took to allow massive 1/f ingress.

OK you got me. What does star-pointing every track around the input mean?


Sorry, I meant every ground track and every HT track with decoupling.

d

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