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Author Topic: Background Radiation - Could It Be a Vexation ?  (Read 41435 times)
AG6K
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« Reply #15 on: October 23, 2011, 01:25:19 PM »

Quote
AG6K  says:
Quote
  The reason I started this thread is because two days ag I received a telephone from an Ham in Idaho whose 8166/4-1000A amplifier  had an event when it was in Rx / biased off.

Quote from: 2E0CHE on Today at 10:38:44 AM
Quote
Interesting, but I would be looking elsewhere.
Regards, Dan.

The common cause of a faults on standby is a gassy tube, although sometimes it can be a HV fault outside the tube. I've seen dozens of cases where a tube will arc on standby. None of it is anything more than a simple tube fault.

  The 8166 is not gassy.
Rich
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AG6K
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« Reply #16 on: October 23, 2011, 01:35:20 PM »

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Quote from: AG6K on Today at 09:48:14 AM
I was thinking about it striking any atom in a tube and knocking one or more electrons loose -- thereby causing the tube to briefly conduct due to the several kilovolts present. 
Work the numbers, gate capacitance, charge on an electron... delta V on the gate.

  4-1000As have no gate.

Quote
Lets assume a 1pf gate/cathode capacitance (more makes the effect smaller), then knocking an electron off and having it accelerate to a large distance will change the grid voltage by delta V = delta Q /  C = 10^-19 / 10^-12 = 10^-7 V  (Working to orders of magnitude).
It takes 10^7 electrons to change the bias by a volt given a completely open circuit grid @ 1pf...... The only way you are getting that is if the tube avalanches, and if there is enough gas for that you have worse problems (Or you have a hunk of Cs137 on the shelf behind the amp in which case you also have worse problems).

Quote
The reason I started this thread is because two days ago I received a telephone call from an Ham in Idaho whose 8166/4-1000A amplifier  had an event when it was in Rx / biased off.
Interesting, but I would be looking elsewhere.

Regards, Dan.

  Where?
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M0HCN
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« Reply #17 on: October 23, 2011, 02:02:20 PM »

4-1000As have no gate.
Ok so I have been doing too much with fets lately....
The math still applies to the grid just the same as it did to the fet gate.

Faulty tube/socket/insulation failure/bias supply fault, something of that type would be my guess.

When fault finding assume the simple faults until you really do need to introduce weird physics (the second type of fault are **RARE**), 99.99%  of the time even the weird ones turn out to have a (with hindsight) trivial cause.

Also, it is often a bad idea to take user reports at face value, "Nothing has changed" then after a week of headscratching it turns out that "Nothing" includes a new PTT cable or upgrading the software or whatever. Been there, the judge ruled it justifiable homicide...... 

Regards, Dan.
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AG6K
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« Reply #18 on: October 24, 2011, 04:35:09 AM »

Quote
AG6K  says:
Quote
  The reason I started this thread is because two days ag I received a telephone from an Ham in Idaho whose 8166/4-1000A amplifier  had an event when it was in Rx / biased off.

Quote from: 2E0CHE on Yesterday at 10:38:44 AM
Quote
Interesting, but I would be looking elsewhere.
Regards, Dan.

Tom Rauch:  The common cause of a faults on standby is a gassy tube, although sometimes it can be a HV fault outside the tube. I've seen dozens of cases where a tube will arc on standby. None of it is anything more than a simple tube fault.

  Tom R.:  The 8166/4-1000A is not gassy. The owner of the 8166/4-1000A amplifier told me he had an external arc because at the he was looking in the direction of the blue flash and he heard a loud bang.  An arc inside a tube does not go bang, it goes tink.  There was no damage to the bias components.  The owner told me what he thought it was but I know you aren't having any of that Tom.  cheers
Rich, ag6k
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W8JI
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« Reply #19 on: October 24, 2011, 07:22:51 AM »

  Tom R.:  The 8166/4-1000A is not gassy. The owner of the 8166/4-1000A amplifier told me he had an external arc because at the he was looking in the direction of the blue flash and he heard a loud bang.  An arc inside a tube does not go bang, it goes tink.  There was no damage to the bias components.  The owner told me what he thought it was but I know you aren't having any of that Tom.  cheers
Rich, ag6k


That's just your take on it. None of that in any way indicates the tube was not gassy.

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AG6K
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« Reply #20 on: October 24, 2011, 08:55:17 AM »

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W8JI
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RE: Background Radiation - Could It Be a Vexation ?
« Reply #19 on: Today at 07:22:51 AM »
   
Reply with quoteQuote
Quote from: AG6K on Today at 04:35:09 AM
  Tom R.:  The 8166/4-1000A is not gassy. The owner of the 8166/4-1000A amplifier told me he had an external arc because at the he was looking in the direction of the blue flash and he heard a loud bang.  An arc inside a tube does not go bang, it goes tink.  There was no damage to the bias components.  The owner told me what he thought it was but I know you aren't having any of that Tom.  cheers
Rich, ag6k


That's just your take on it. None of that in any way indicates the tube was not gassy.

  The owner told he subsequently checked the tube and it was not gassy.   Would an anode-to-gnded grid arc  inside a gassy tube make a bang Tom ?
Rich, ag6k
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M0HCN
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« Reply #21 on: October 24, 2011, 09:13:16 AM »

Not directly, but I could see magnetorestriction in the wiring and possibly even the power transformer making a bang as the current pulse sets up fields between conductors.

I have actually heard this effect in pulsed power applications, the intake room had a sort of ghostly impossible to locate ticking sound coming from everywhere as the wiring in the conduits reacted to fast risetime pulses.

Regards, Dan.
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W8JI
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« Reply #22 on: October 24, 2011, 09:18:34 AM »

  The owner told he subsequently checked the tube and it was not gassy. 
 


So what? My wife tells me numerology works. People say things, claim things, and think things all the time that are not factual.


Quote
Would an anode-to-gnded grid arc  inside a gassy tube make a bang Tom ?
Rich, ag6k

Yes, if coupled to an outside system it does. It absolutely happens all the time.

When we produced a 3CX3000F7 amplifier new tubes would fault all the time on power up. They would always make a big bang as resistors and unintentional air gaps would arc, and wires jump around during the fault. One big bang, and the tubes would be clear for life.
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AH6RR
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« Reply #23 on: October 24, 2011, 10:03:23 AM »

I have come to the conclusion that Rich was very good friends with Timothy Leary back in the 60's
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AG6K
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« Reply #24 on: October 24, 2011, 12:16:28 PM »

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AH6RR
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RE: Background Radiation - Could It Be a Vexation ?
« Reply #23 on: Today at 10:03:23 AM »
   
Reply with quoteQuote
I have come to the conclusion that Rich was very good friends with Timothy Leary back in the 60's

  YWhat was his callsign?  .  Do you believe that an arc inside a vacuum tubes makes a big bang? 
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W8JI
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« Reply #25 on: October 24, 2011, 01:24:14 PM »

  YWhat was his callsign? 


AC1D

Quote
Do you believe that an arc inside a vacuum tubes makes a big bang? 


I do, because I've seen and heard it on many occasions.

Apparently many others do, also.
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AG6K
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« Reply #26 on: October 24, 2011, 06:19:34 PM »

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W8JI
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RE: Background Radiation - Could It Be a Vexation ?
« Reply #25 on: Today at 01:24:14 PM »
   
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Quote from: AG6K on Today at 12:16:28 PM
  What was his callsign?
.

AC1D

Quote
Do you believe that an arc inside a vacuum tubes makes a big bang?


I do, because I've seen and heard it on many occasions.

  I remember in high school physics when the instructor put an electric alarm bell in a bell jar, started the current through it and began pumping the air out.   At first the class could hear the bell plainly but as the vacuum  increased the sound level decreased.  When the pressure in the jar was <1mm of Hg the sound was barely there. 
  ••  "You can fool some of the people some of the time,  but you can't fool all of the people all of the time "
-  Abraham Lincoln

Quote
Apparently many others do, also.

  Apparently are others who think it's possible to make stuff up and win a science debate. 
Rich, ag6k
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AG6K
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« Reply #27 on: October 24, 2011, 06:25:14 PM »

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Quote
Would an anode-to-gnded grid arc  inside a gassy tube make a bang Tom ?
Rich, ag6k

Tom R.  -- Yes, if coupled to an outside system it does. It absolutely happens all the time.

  Tom's "System" prestidigitation again.

Rich, ag6k
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AH6RR
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« Reply #28 on: October 24, 2011, 07:42:21 PM »

To funny Tom that is about right and I thought it was W60LSD since he was on the left coast.
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N3OX
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« Reply #29 on: October 24, 2011, 08:36:48 PM »

I have actually heard this effect in pulsed power applications, the intake room had a sort of ghostly impossible to locate ticking sound coming from everywhere as the wiring in the conduits reacted to fast risetime pulses.

I have a split ferrite core on a stepper motor controller for one of my antenna switches that ticks when I change bands Grin
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
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