>
>Rich:
>
>You keeping adding new twists to assure failure.
>
>Your statement . "The DAF runs heavy grid current" is no more true than the
>statement that any grounded amplifier draws heavy current.
>
We are discussing grid driven amplifiers. Normal grid driven linear
amplifiers draw virtually zero grid current. GAF amplifiers are grid
driven and they draw grid current.
>At maximum drive, the plate, screen, control grid, and filament of both the
>grounded cathode and the G2DAF circuit will have the same voltages (when
>adjusted correctly).
When the AB1 amplifier is adjusted correctly, there will No positive
potential on the grid. When the DAF is adjusted properly, there will be
positive potential on the grid.
>So, the G2DAF circuit will draw no more grid current
>than the standard grounded cathode configuration.
? really?
>By defining the G2DAF as
>drawing grid current at maximum signal, you assure failure.
>
? correct.
>According to Bill Orr, in his article "Intermodulation Distortion in Vacuum
>Tubes", "as far as IM distortion goes, (the perfect tube) is a poor device
>to use in equipment designed for linear amplification". However, he
>explains that the practical tube in fact will provide less distortion.
>Speaking about the curve of the practical tube, he states "the central
>portion is fairly linear and the lower portion resembles a parabola". The
>G2DAF circuit simply extends the parabola. Compression at the top end of
>the curve is the biggest cause of distortion, and the G2DAF circuit may
>actually reduce this by increasing the screen voltage at the peak.
>
? I don't see how.
>The Orr article assumes a constant screen voltage, but does state that (at
>least for a portion of the bottom end of the curve) the parabola is not only
>not harmful but exists in practical tubes which actually have less
>distortion than the "perfect" tube.
>
>Orr states that "the magnitudes of the intermodulation distortion products
>are significantly affected by almost everything: changing heater or filament
>voltage by only a few per cent; slight shifts in bias voltae, idling
>current, screen voltage, plate or grid tuning, neutralization, loading - all
>of these factors and others even more obscure enter into the determination
>of intermodulation distortion". Varying the screen voltage is simply one of
>a number of factors to be considered.
Screen potential is a large factor in electron ballistics. A change in
screen potential exponentially changes peak anode current by (e1/e2)}^1.5
. The reason that the screen potential is fixed is to maintian fixed
gain with changing drive levels - a must for minimal distortion. .
>
>The fact that the two amplifiers you have listened to
and measured
>had splatter does not
>prove that the circuit will not work.
It quite certianly worked. The P output was about 20% above normal and
the distortion measured about ten db above normal.
>To the contrary, your reports of the
>813 amplifier in the G2DAF circuitry were consistent with what one would
>expect using the same tube in stabilized screen grounded cathode circuitry
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