>Esteemed Reflectees:
>
> The comments expressed recently regarding adding a second tube to
>the existing one in the Alpha 77 series, without altering the tank, has made
>me think about the practice as it applies to other amps. I noted lots of
>folks are adding a 3rd 8874 to their older Alphas, and the current AL-800
>will apparently ...
...allegedly seems to be a bit more like it.
>...take a second 3CX800A with no other PS or tank changes to
>make it an AL-800H. Possibly someone else makes a 1-holer ready to take a
>second tube.
To yield a tank operating Q of 12 with two tubes (operated at double the
anode current of a single tube), a 1-holer that is "ready to take a
second tube" would need an original tank operating Q of 24.
>
- For example: When the second tube is added to a 77dx, and the tubes
are driven to 2A of anode current, the stock tank's operating Q on 160m
drops to about 5.9. IMO, this is not good engineering practice. To
increase the operating Q to 12, C-tune and C-load need to be roughly
doubled and L needs to be roughly halved. Since P=I^2 *R, it might be
worthwhile to increase the surface area of the tank inductors when the
second tube is added--because the RF circulating current doubles.
- Are we to believe that recognized amplifier "experts" are exempt from
Ohm's Law?
Rich---
R. L. Measures, 805-386-3734, AG6K
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