On Thu, 26 Oct 2000 21:24:20 +0200 Peter Sundberg <sm2cew@telia.com>
writes:
>
Hi Peter,
>I have to say that Colin and Marv seems to be the most open minded
people
>on this reflector at the moment.
Complements are gratefully accepted.
>At least they try to understand what is
>going on and even suggest some improvements.
>
>Two tone tests have been used as a standard to evaluate amplifiers since
>donkeys years. Now this test is not telling the truth say's the gurus..
ok,
>I accept the doubts on given grounds.
>But maybe we should start testing other amps than DAF's without using
the
>two tone test. A poorly regulated screen power supply in a grid driven
amp
>should maintain a pretty stable voltage with a two tone constant
modulation
>not giving away that the amp would sound bad when modulated by speech.
>True or not .. ?
IMD testing using white noise is possibly a more accurate methodology
and more representative of a real world voice situation. A good
description of the technique may be found in "Single Sideband, Systems &
Circuits" by Sabin & Schoenike, 1987 pp 473-477.
Here in the states, I believe that the FCC still uses the two tone
standard for their distortion tests so, it makes sense that if that is
the test you need to pass, that is the test you run.
>But I do most certainly agree with Marv and Colin that the DAF circuit
is
>not going to work with every tube on the shelf, the 4CX250's for
instance
>are a NO GO for sure. Just like some tubes don't work in GG.
I reallllllly hate to say this but, 4CX250's are not necessarily
disqualified for use in the DAF configuration. They are spec'ed for 2
watts grid dissipation. And my 1968 RSGB ham radio circuits book shows a
4X150 (essentially the same tube) version with some minor circuit mods on
the page facing the original DAF.
It may be have been forgotten by now... but, when I got entangled in
this thread 24 hours ago, I specifically stated that I am NOT an advocate
for the DAF concept. I just like to see the facts & numbers kept neat!
:-)
73,
Marv WC6W
*
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