Re: MC PHONO PREAMP



Ian Bell wrote:

Patrick Turner wrote:

Paul Crawford wrote:
snip

I have yet to come across any work that verifies the old 2.5/gm
equivalent input noise resistance for a tube. I have yet to see better
than 2uV from a single tube.

The EINR isn't the only source of tube noise. There is shot noise at the
anode. And the noise spectra has more amplitude at low F.

But your'e right, not all tubes measure less than 2uV of calculated
input noise. I have a few with 0.8uV though, rather rare.....

One has to measure the noise after an amp raises the signal at the anode
of a tube under test x 1,000 times then divide the noise figure by a
total of [1,000 x tube gain]. We assume the noise at the anode of the
tested tube is mainly all due to EINR. Its difficult to measure it any
other way.

The noise of the tester amp with gain of 1,000 will not significantly
contribute to noise measurements.

Patrick Turner.

Cheers
.

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