[AMPS] VHF visitation (was power handling...)

[measures]

>Rich says;
>
>>I have never been able to find an arc mark in a tube that grid-fil. 
>>shorted during a big-bang event.  
>
>According to Gossling's paper, 'tree like markings' appear, but they can be
>quite small. He goes on:'If the discharge current passes through two limbs
>of a filament placed side by side, these are often pulled together by the
>magnetic attraction of the parallel currents, causing a short circuit and
>spoiling the valve', which sounds  very much like the filament heix bending
>you've observed, Rich.

 I saw this in the prototype for the AL-811   The filament wires were 
pulled together and they broke into pieces that dropped into the bottoms 
of the envelopes.   With a dipmeter tuned to 85MHz, I observed a sharp 
dip at the blocking cap. 
>
>Question: when these 'big bangs' occur in amps with paralleled tubes (such
>as 3-500Zs), do both tubes go west, or only one?

In amps.  with typical 500va  anode supplies -  like the SB-220 and 
TL-922, one tube may short after a big bang.  However, such shorts 
typically appear only when the fil. is lit.  .  In the Henry 3K-A, one 
finds a 2500va CCS supply and no glitch resistor in the positive hv lead. 
 When a 3K-A has a stentorian event, both tubes often dead short by 
welding the grid to the anode.  We have never been able to straighten the 
filament helices in such a tube with our 11g centrifuge.  .  //  I know 
of one 3kA in Manhattan Beach, CA and one 3k-A in Santa Monica, CA that 
managed to short two pairs of brand new, out of the Eimac factory sealed 
box, 3-500Zs in under 24 hours flat.  .  

Jim Day, the man who bought the orig. "Plywood Box" 8171 amplifier, 
repairs and modifies Henry amplifiers as a sideline.  Over the years, he 
has become friends with the guys who build Henry amps in LA.  One day he 
told the Henry guys that he has been able to apparently stabilize unruly 
Henry amplifiers by installing lower VHF-Q suppressors in lieu of Henry's 
silver plated beauties.  The Henry guys said that they could not change 
their suppressor in any way because this is the way that they have been 
making them since the very first day.     .  
>
cheers, Peter

-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


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