[AMPS] SB-220 TUNE Cap Arcing

[Rich Measures]

>>>I was under the impression that some of the mods he did on the input side 
>>>might have been adding nichrome suppressors to the grid leads like you 
>>>suggest.  
>>
>>The resistance-wire grid-grounding suppressors I recommend for the 
>>4-1000A/8166 do not increase or decrease the inductance in series with 
>>the grid.  Such suppressors decrease the Q of the unavoidable VHF grid 
>>resonance. 
>
>I am confused.  First we were on the 3-500Z of these guys amp, now on the 
>4-1000A.  

The 8166 has a tricky screen grid resonance.  The 3-500Z grid can be 
grounded with two resistance wire conductors of different lengths, at 
right angles to each other, using separate gnd lugs.  The resonance point 
will be roughly the same (80MHz) as with conventional grounding, however, 
the Q will be lower.  //  Conductor width is a logarithmic function in 
Terman's inductance of straight conductors formula, so there is little 
difference in inductance between a foot of #1 and a foot of #18.  

> Anyhow, Rich adding any kind of thin wire to a grid to ground 
>path vs. having the grid directly grounded with a very short piece of 
>braid does add more inductance.  

Not as much as some folks might imagine.  A dipmeter tells what's what.  

>However, sometimes adding the inductance 
>is necessary for moving the resonance point.
>
In the case of the 8166, yes.  Generally speaking, for triodes, 
increasing the grid resonance freq. increases stability.  
>
-  later, Jon

Rich. Measures.  Web site:  www.vcnet.com/measures


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