[Amps] R. MEASURES PRAYERS ANSWERED

[R L Measures]

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 at somis.org