[AMPS] Follow Up on the SB-220 Follow UP

[Rich Measures]

>>> If you 
>>>think that he had a parasitic event while unkeyed, please explain how 
>>>this could happen.  I always belived that a tube in cutoff would be very 
>>>hard to get oscillating.  You also told me this once.
>>>
>>€  The how part beats me.  It has not happened to me, however, I have 
>>talked to a number of those who have had it happen.  How do we know it 
>>was a parasite?  Bent fil. helix / sudden change in suppressor resistance 
>>/ 6kV bandswitch arcs in amp. with 3kV anode supply, are clues.
>
>I guess it happens to those who think that every bang is a parasitic 
>oscillation.  For one, with proper suppressor resistors you shouldn't have 
>an oscillation.  

€  The Challenger o-rings were supposed to be plenty ok in cold weather.  

>I don't think the oscillation changes the value of the 
>resistors.  

€  A big-bang event happens in a 2-holer..  The suppressor resistors are 
100 ohm +/- 5% units.  The resistors appear to be in mint condition. .  
Each resistor is virtually shorted by a few turns of #16 copper wire.  
The measured resistance of the suppressor resistors was over 400 ohms.   
I was there.  I made the measurements.   

>Rather, I think the resistor values change over time and over 
>being heated up.  Then you can get an oscillation because of bad resistors 
>and hence a suppressor not performing properly.
>
>But the only thing that blew in this guy's amp was a resistor.  Don't 
>think he had the beloved parasite.
>
€  If he has a bent fil. helix, my guess is that either he has been using 
the amp. in an aerobatic aeroplane, or he had an intermittent parasitic 
oscillation. 

-  later, Jon


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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