[Amps] AL-80B questions

[rlm]

>Rich-
>
>Somethings I've always wondered about...
>
>determining the required inductive component of the 'suppressor' for a 
>particular amp.

**  for optimum effectiveness, the suppressor inductor (L-sup) needs to 
have roughly the same # of ohms of reactance (at the anode's vhf-resonant 
frequency) as the ohms of the suppressor's resistor.  This arrangement 
divides the vhf ringing-current semi-equally and optimizes the 
stagger-tuning effect that broadbands (decreases the Q) of the vhf 
resonance and proportionately decreases the damped-wave ringing potential 
when anode current changes.  
>
>the problem is positive feedback through coupling between the plate 
>circuit and the
>grid circuit. right?

**  In a tetrode or pentode, right.  In a g-g triode, the problem is 
coupling between the anode/plate output and the cathode input.
>
>In order to get enough feedback for an unwanted oscillation, we need a 
>resonant circuit, right? 

**  correct.  And there always is a VHF-resonant circuit in a HF 
amplifier.  The lowest freq I've seen in a HF amp was 43MHz (4cx20,000A). 
 the highest was 170MHz (8873).

>The inductive component of the suppressor changes the resonance, 
>to a frequency where we can not get enough feedback to sustain oscillation, 
right? 

**  Shorted or not shorted, L-sup/R-sup barely shifts the anode circuit's 
resonanant frequency.

>If so, this means the
>inductance does not have to be some specific value, so long as it's 
>enough to move the
>resonant frequency enough.
>
>So what's the resistor for?

**  The resistance lowers Q which lowers peak ringing V, and it provides 
a low-L path to establish the stagger-tuning effect.  Resistance in the 
inductive path also lowers Q.  
>
>Isn't this the same thing we do when we neutralize a tube with 
>additional capacitance
>in the feedback loop? 

**  no

>Why isn't this additional capacitance damped? 
>Should it be?
>
**  The Bruene neutralization bridge needs to be tuned for minimum SWR at 
the operating freq. - which cancels grid reactance.  When this is done, 
the C-divider is then adjusted to null the feedthrough signal at the 
anode.  Since a uniform 180º phase shift is needed over the entire 
operating range in order to cancel feedback at the operating freq., 
adding R would seem be a hindrance.  [see Figure 5 on my Web site]

cheers, Bob

-  R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K, 
www.vcnet.com/measures.  
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