[AMPS] Another arc question

[Rich Measures]

> 
>>
>>>>4E27s  from the same lot were quite gassy, presumably due to 
>>imperfect 
>>>>metal/glass seals.  
>>>
>>>Are you now confusing or mixing up "gas"  Rich.  Gas due to imperfect
>>>seals is not the same as gas released internally from the materials. 
>>
>>The point is that gas is not gradually absorbed by a getter -- i.e., 
>>the 
>>rauchian disappearing gas theory does not wash.  However, the basic 
>>problem is that gas is seldom found in tubes with bent filament 
>>helices / 
>>a filament-grid short.  
>
>But you still did not answer the question Rich..sounds like a rauchian
>evasion IMO.
>A getter has nothing to do with "gradual" gas absorbtion. The anode is
>the culprit and the getter is the cure according to my understanding.
>Maybe we are just saying the same thing in a different way.
>
I am saying that I have seen gassy 3-500Zs, and the gas does not 
disappear, and that filament/grid shorted 3-500Zs very rarely exhibit gas 
leakage.  I have never seen arc-marks in a filament/grid shorted 3-500Z

> In a tantalum plate tube the plate must show color for the getter to
>even begin to do its job. A typical SB-220 owner will rarely, if ever,
>get his amp into the condition necessary to harden the tubes.
>Note that I keep stressing the SB-220 since it is probably the most
>common 3-500 amp ever built and in use today. For the time being I dont
>care squat about any other tube...lets just agree to stick to the 3-500
>and the SB-220 since we and many readers are all  very familiar with it.
>

>>
>>>I also suspect that your microamp hipot tester will not be capable of
>>>creating the conditions necessary to recreate a gas discharge 
>>event...
>>
>>It matters not whether the high potential supply being used to measure 
>>
>>gas leakage is capable of 1mA or 1000A.  
>
>I disagree. A microamp hipot tester will not be capable of any plasma
>generation..if you want to try and duplicate the fault conditions.
>
My highpot tester has plenty of current capability to create a gas plasma 
in gassy tubes.  The bluish plasma glows plainly in a darkened room.    
>>
>>>but I will leave that to Arlen and others with a formal education to 
>>comment 
>>on.
>>
>>>Sometimes it takes a 2x4 approach to get a persons attention Arlen. I
>>>think your message was well put and I know that I learned from it.
>
>>>As has been mentioned here numerous times...how do you know the 
>>condition
>>>of the resistor minutes, days or weeks before the arc?  Unless you 
>>can
>>>recreate the event in a controlled experiment I fail to see why you
>>>continue to harp on the resistor.
>>
>>because the suppressor resistor is virtually shorted out by  
>><1-milliohm 
>>of copper buswire that typically has 0.08 uH of L, which should 
>>protect 
>>it from DC arcs in the tube, but which would not protect it from 
>>bursts 
>>of vhf energy.  .  
>>
>>>In the case of the SB-220 would not the almost instantaneous 
>>discharge of
>>>the 3200VDC ( in standby which is where most arcs appear to occur) 
>>>not cause damage to the resistor? 
>>
>>no, no
>
>YES YES IMO
>
You have not satisfactorily explained how a 50 - 100 ohm resistor that is 
shorted out by 1 milliohm of copper buswire can be damaged by a DC anode 
arc which mysteriously leaves no arc craters in the filament-grid shorted 
tube.  
>>
>>>Would not the field developed in the
>>>suppressor L be sufficient to "bend" the carbon in the resistor causing
>>>the case to crack?  

no

>>>If one were to believe that the magnetic field 
>>>caused the filament to bend then the same reasoning would hold for the
>>>resistor...at least it makes sense to this uneducated dummy.
>>>
>>not to yours truly
>
>Why not?  If I'm wrong please educate me. I promise to not ask a months
>worth of useless questions!
>
Carbon granules do not bend.  Wire bends.  
>>
>>>Rich has also failed to ever explain how an amp in standby, biased well
>>>beyond cut-off can suddenly have a parasitic event.  Particularly in 
>>>an amp that is completely stable when keyed with no drive and the Tune 
>>>and Load caps are varied in an attempt to force a parasitic.
>>>Not to be confused by external arcs in tank circuit components while 
>>>the amp is in a RF amplifying state.
>>>
>>Only 5% or so of the parasitic oscillations I hear about fall into 
>>this  category,
>
>Yet, almost 100% of my customers and reports here indicate the bang is
>during standby. Again...ONLY the SB-220 is discussed here. Heck, throw in
>the TL-922 also if you want.
>
>> however, the open contact gap in a typical cathode bias 
>>relay is only 25 thousandths, which is easily broken down if the tube 
>>conducts for a microsecond or so for who knows whatever reason. 
>
>I may be missing your point but I doubt if the relay path is ever an
>issue during a catostrophic arc....

Are you contending that current that causes the damage to the 
cathode/filament passes through the 10k to 100k ohm cutoff bias R?   The 
only paths of current to the cathode are through the relay contacts or 
through the cathode cutoff bias resistor.  .  I doubt that the current 
needed to blow a 1A grid-gnd RFC could be passing through the cutoff bias 
R, which leaves only the relay contacts.  . 

>I've never replaced one (a relay) for that reason.

 There is typically no fatal damage to a relay whose contacts have 
sustained a brief arc. 


cheers
Rich...

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


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