On May 31, 2006, at 8:50 AM, k7fm wrote:
> "True, however, prayer cloths are not all that reliable. The main
> reason for going after a parasite in the anode circuit is that it's
> where the damped wave VHF ringing takes place - whenever anode
> current changes - that starts the snowball rolling downhill."
>
> It is also possible that a parasitic suppressor is an admission of
> sloppy design work. There are many amplifiers built using the 8877
> tube with no parasitic suppressors. Can you imagine installing a
> parasitic suppressor into uhf cavity? Perhaps you can make the
> entire cavity out of nichrome.
VHF and UHF amplifiers are inherently more stable because they do not
have two resonances in the anode circuitry.
>
> When designing an all band hf amplifier, it is probably easier to
> throw in a parasitic suppressor for the assumed
> natural frequency of oscillation in the existing structure than to
> use a network analyzer and a lot of effort to reduce the
> oscillations to a point where they no longer will occur.
>
> Rich talks about prayer cloths - but in fact his nichrome
> suppressor is acting as a prayer cloth. This is a case of putting
> that in will make sure something bad will not happen. It takes
> confidence in ones ability to build an amplifier without one -
> because they you are relying on your skill as a designer and
> builder - and expertise in measuring.
No divine assistance is needed to decrease VHF-Q. Add R, Q drops,
the anode's parallel-equivalent R decreases, and VHF gain decreases.
>
> I have built amplifiers with and without parasitic suppressors and
> have had parasitics in both - but then again, I am only an amateur.
My novice-days 813 amplifier never had a parasite and it never had a
suppressor.
>
> 73, Colin K7FM
>
R L MEASURES, AG6K. 805-386-3734
r@somis.org
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|