[AMPS] Another arc question
km1h@juno.com
km1h@juno.com
Thu, 07 May 1998 21:31:19 EDT
>
>>>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.
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.
>
>>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
>
>>Would not the field developed in the
>>suppressor L be sufficient to "bend" the carbon in the resistor
>causing
>>the case to crack? 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!
>
>>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....I've never replaced one for that
reason.
73 Carl KM1H
.
>
>cheers
>Rich...
>
>R. L. Measures, 805-386-3734, AG6K
>
>
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>
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