>
>> >Barnacles are described in many texts. Copper actually grows
>> >barnacles when in a vacuum.
>>
>> [chortle] these are long copper filaments that burn away easily. Are
>> 3-500Z anodes made from copper? > >This entire topic has been discussed
>> here before.
>
>3-500's primarily fail from gas or mechanical problems like bad
>welds.
>
>Several tubes out of the last batch of 100 3-500Z's from Varian in
>Salt Lake City before the power grid facility was closed all had long
>single strands of grid wire sticking out of the top of the grid.
>
>All 100 had to be replaced, due to arcing.
>
>> Ä We have heard taurine feculance here before..
>
>It seems to follow you.
? Mr Rauch plays the Ad Hominem card.
>
>> I have opened dozens of kaput 3-500Zs from amps that reportedly had a
>> big-bang. I have yet to see a barnicle.
>
>3-500's don't have copper cooler. 8877's and such do. Barnacles
>are small and fragile, and disappear after an arc. They are common
>in vacuum capacitors also.
? vacuum caps tend to accumulate long whiskers of copper during storage.
Whiskers are not barnacles. I have never seen an 8877 grow whiskers.
>
>> >Tube faults like that are intentionally removed by controlled arcing, and
>> >uncontrolled flash will do the same thing.
>> >
>> >If the tube repeatedly arcs, it needs to be replaced.
>> >
>> >I'm more interested in your claim the grid fails to be a shield in the
>> >3-500Z at 80 MHz, and the grid capacitors raise that frequency. How do
>> >you determine that?
>> >
>> A dipmeter. If the grid were resonant where you claim, the amplifier could
>> not oscillate at c. 110MHz.
>
>The amplifier does NOT oscillate at "c. 110 MHz, as you claim, when the
>grid is directly grounded.
>
[chortle]
>The AL80 series, if the parasitic suppressor is removed and a grid
>wire or two lifted, oscillates near 180 MHz. It is a repeatable
>oscillation that can easily be measured.
As I recall, during the Grate Parasitics debate, the claimed frequency
was different.
>
>> >If I do a plot of S12 or S21 on a cold tube in a test fixture, would you
>> >like to put it on your web page and remove the incorrect data?
>>
>> If no such dips occur in a SB-220 at the frequencies you claim, the
>> ''incorect data'' is not mine.
>
>Your mistake is rooted in your lack of test equipment. A grid dip
>meter held near the grid connection to chassis can not determine
>the parallel resonant frequency of the grid.
>
>It could be measuring almost anything, because it is the wrong
>device for the job.
>
? This is only your opinion.
>The only way to measure the grid's isolating or shielding effect
>between the anode and cathode is to measure the loss through the
>tube from anode to cathode, or vice versa, on a cold tube in the
>actual circuit.
Before you said you used a test fixture
>
>I'm sure you think you measured something useful, but the fact is
>you have no idea what the grid impedance is using your method.
>This is especially true when there are capacitors involved, and
>multiple grid pins.
I tried it directly grounded and grounded through caps. The difference
was about 1MHz.
> You easily could have measured the loop
>impedance from chassis to grid support and back to chassis again,
>including the path through the chassis.
>
This is why I made measurement checks both ways. The same precaution
applies to the use of a Impedance Meter.
>Even if you isolated a single pin, the measurement would still be
>invalid because it does not determine the impedance at the grid.
>
This is not what the measurement is for.
>On the other hand when the signal attenuation is measured from
>cathode to anode, the effects of grid shielding can be clearly seen.
>
A dip on a dipmeter can clearly be seen.
? When reading Mr Rauch's posts, it is important to compare what he
writes with the post he is supposedly replying to. What Mr. Rauch
tosses off is usually more important that what he says.
>
Later, Tom
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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