>Rich, you wrote:
>
>? I have a theory on this. /// In my opinion, some guys use the DAF
>config. as an
>attention-getter and ego-builder. According to phychologist Dr. Phyllis
>Greenacre, some men use such tools to promote male-competence. . . .
>"The sense of reality is characterized by a peculiarly sharp, quick
>perceptiveness, extraordinarily immediate keenness and responsiveness,
>especially in the area or the imposture. The sense of reality is,
>however, impaired."
> [Phyllis Greenacre: "The Impostor" Psychoanalytic Quarterly, 27:359 -
>382 (1958)]
>
>GOOD WORK, RICH! Trial lawyers have stated that if the facts are on your
>side, you argue the facts. If they are not, you argue the law. If the law
>is not on your side, then you argue the Constitution. If that is against
>you, you argue about the other lawyer's tactics. You have added a new one -
>psychoanalysis. I will remember to use that when reasoning and the facts
>fail me.
>
-22db or so down is what the DAFs measured.
>The reason that an amplifier using screen voltage derived from the drive may
>work is as follows:
>
>We know that at fulll drive, the screen will have exactly the same voltage
>on it whether it is derived from a separate regulated circuit or from a
>rectification of the drive.
Si, Correcto
>Therefore, the G2DAF circuit will have exactly
>the same distortion products at a constant full drive as the standard
>configuration.
Hardly. AB1 has zero grid current. The DAF runs heavy grid current.
> We also know that at zero drive, there will be no distortion
>products.
? Duhh
>So, if a tube such as the 813 is used in a G2DAF circuitry, it
>must fail because that tube is not a good tube to use in a grid driven
>circuitry. The 813 would have unacceptable distortion products even if the
>screen voltage was regulated perfectly.
? True enough. The 813 was designed for Class C.
>
>What is questioned is what happens between zero and full drive. This is one
>case where the G2DAF circuitry has an advantage over the standard
>configuration, because the gain of the amplifier tube changes with drive.
? The gain of an amplifier tube needs to be constant at any drive level
to be linear.
>Since distortion is measured against full output,
? Not the way I measure distortion. The human voice has rapidly varying
amplitudes.
> the G2DAF circuitry will
>actually inproved distortion products as drive decreases - because the gain
>of the tube is less.
>
? I do not see how this the case.
>The gain of the amplifier using a regulated screen is constant. We know
>that tubes are not inherently linear and even using a very regulated screen
>will result in distortion products. Eimac rates the 4CX250B at -25 db 3rd
>order distortion below peak power with the standard grounded cathode
>configuration.
Eimac rates it at -25db below either tone of a two-tone, which is 31db
below peak.
>As the drive is varied throughout speech, distortion will
>occur and this distortion will be amplified at a constant gain.
>
? ¿?
>Varying the screen voltage probably increases distortion, however it could
>be offset by a decrease in gain of the tube.
>
>The real question is how fast can the screen voltage follow the driver
>signal. Since the rectifier charges a capacitor, we need a time constant so
>fast that the screen voltage charges immediately. This could be a
>significant problem, and may cause the circuit to fail in practical use. It
>may be similar to the use of audio derived agc. In most cases, the agc will
>not follow speech and the first impulse of the received signal will cause a
>clicking. What you hear in a receiver as clicking would be severe
>distortion during transmission. I know I could make the G2DAF circuitry
>fail and splatter by delaying the charging of the screen, but it may be
>possible to charge the screen fast enough to have it faithfully follow the
>grid. By using circuits similar to agc circuits, it should be possible.
>
>Easy, heck no!
Impossible, yes. Norm kept coming up with new and greatly improved
screen configurations for his DAF amplifier. Distortion was c. 22db
down. .
>
>It is obvious that other parameters need to be followed, such as adequate
>bypassing of the screen.
The only proven workaround for not regulating the screen is G-G.
cheers, Colin
- Rich..., 805.386.3734, www.vcnet.com/measures.
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