[AMPS] B+resistors

[Rich Measures]

>Rich,
>
>>Special, high peak energy-absorbing resistors are best, 
>>although the cost is high.  
>
>Have you any comments about using big solid carbon or metal film
>resistors - things like 50ohm, 50 watt metal film tubular resistors NOT
>spirally cut, as are/were made for dummy loads? 

Spiral-cutting would reduce the voltage-gradient in the resistive 
material.  

>Similarly,  the carbon
>things about 10 inches long and 1 inch diameter?

My opinion is try it.  If the resistor does not fail during a test, it's 
probably going to do the job of limiting peak fault current during a real 
glitch.  //  Carborundum Co. made special high peak energy-absorbing 
resistors before they were bought out by Cesivid [716 286 7610].  The 
Cesivid catalog lists similar resistors.  //   To test a glitch resistor, 
temorarily short the positive HV to chassis-ground.  If the resistor 
exhibits no sign of damage, you have a winner.  If a glitch diode shorts 
during the test, try replacing it with with 2 of the same type diodes in 
parallel - or with a higher peak-current rated unit.  
>
>Your comments on the failure analysis of the tubes you've looked at does
>suggest that maybe the glitch resistor is not as important...

IMO, the glitch resistor IS important because it limits peak current 
during an intermittent oscillation condition.  I believe that limiting 
peak current during such an event can prevent the aforementioned types of 
grid/filament failure.  

> ...  as has been
>suggested, because arcs per se don't occur. Unless of course, one
>postualtes that the VHF parasitic gets going, and the voltage swing
>achieved at the plate is enough to initiate an arc, leading to all the
>results..........I dunno
>
To be sure, it's a 'whodunit'.  It seems likely to me that the arc is 
external, and it occurs after the current pulse which apparently damages 
the tube during a VHF oscillation condition.  How else could the VHF 
parasitic-oscillation resistor be damaged?  
Rich---

R. L. Measures, 805-386-3734, AG6K   


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