>Can anyone help me with copies of the following articles. I'm having
>trouble finding them locally.
>
>cheers, Paul
>VE7CQK
>email: paul1@wizard.ucs.sfu.ca
>
...snip...
>> ALC for CLass AB1 Amplifiers, QST, July, 1986, 38-39, 47. ***
...snip...
This is an article I missed, Paul.
However, the article should be interesting because the grid's DC bias
voltage in a Class AB1 amplifier is normally adjusted so that, with
full-throttle grid drive, the grid draws ZERO grid current. This means
that the exciter can not overdrive the Class AB1 tetrode (or pentode)
into the distortion-producing grid current region Thus, ALC is not only
not necessary, similar results could be achieved by turning down the
microphone gain AFTER the amplifier is tuned up under maximum signal
conditions.
Note: For anyone who is wondering why the grid bias V adj. was not used
to set the zero signal anode current (ZSAC)--a.k.a. 'idling current':
The next step in the adjustment procedure is adjusting the Screen V to
set the correct ZSAC---which is typically about 1/6 of the maximum anode
current rating. However, if the screen V required to achieve the needed
ZSAC is above the maximum screen V rating for the tube, using a lower
value of grid terminating R is in order. While it is true that the ZSAC
can be fine tuned with the grid bias V adj., the grid V should never be
set so that the grid draws grid current with max. drive applied.
Rich---
R. L. Measures, 805-386-3734, AG6K
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