On Jul 12, 2005, at 8:24 AM, Larry Carman wrote:
> Rich, that's a well know fact in the ham community. I don't understand
> why
> there hasn't been more articles in QST, etc about it and why the FCC
> hasn't
> addressed this issue.
Public discussion of this matter in a respected magazine like *QST*
might raise a stink.
> I never fire up the homebrewed 3cpx5000 amp during
> bacon, eggs and beans burrito consumption.
Better to be safe than sorry.
>
> Fact Or Fiction?
> Regards,
> Larry N5BIP
>
> -----Original Message-----
> From: R; Measures [mailto:r@somis.org]
> Sent: Tuesday, July 12, 2005 9:30 AM
> To: Larry Carman
> Cc: amps@contesting.com
> Subject: Re: [Amps] Tetrodes
>
>
> The operator had a bacon, eggs and beans burrito for breakfast?
> Consumption of such is known to be especially risky around RF
> amplifiers. One theory has it that the salt used to cure bacon somehow
> makes the methane gas produced by the beans in the lower GI tract
> slightly conductive - but only in the presence of strong RF fields -
> but especially so during contests!.
>
> cheerz, Larry
>
> On Jul 12, 2005, at 4:57 AM, Larry Carman wrote:
>
>> What causes the gas release that produces an internal arc?
>>
>> -----Original Message-----
>> From: amps-bounces@contesting.com
>> [mailto:amps-bounces@contesting.com]On
>> Behalf Of Ian White GM3SEK
>> Sent: Tuesday, July 12, 2005 4:14 AM
>> To: amps@contesting.com
>> Subject: Re: [Amps] Tetrodes
>>
>>
>> wrote:
>>>
>>> On Jul 11, 2005, at 11:36 PM, Ian White GM3SEK wrote:
>>>
>>>> wrote:
>>>>>>>
>>>>>>> ... by stopping the flow of current into the screen PS.
>>>>>>>
>>>>>> If the "glitch" is an arc from anode to screen, the mains fuse
>>>>>> won't
>>>>>> protect the screen at all.
>>>>>
>>>>> A tube that arcs from the anode to the screen is already a goner,
>>>>> Ian,
>>>>> so there is nothing of value to protect.
>>>>
>>>> That simply isn't true. Well designed power supplies can protect the
>>>> tube, the anode supply and the screen supply against a wide range of
>>>> faults, including arcs. Many of these faults are completely
>>>> recoverable.
>>>
>>> What condition would make the anode arc to the screen?
>>
>> As many folks will remember from previous repetitions of this topic,
>> reasons for anode-screen arcs include:
>>
>> 1. Loss of load at a phase angle that results in extremely high anode
>> voltages. With certain amps, you can make this happen anytime you
>> wish:
>> remove load, apply full drive - BANG.
>>
>> If the RF voltage is high enough, the anode flashes over to the next
>> lower-potential object within sight. For a tetrode, this is usually
>> the
>> screen, so the screen supply experiences a very large negative current
>> input from the tube.
>>
>> For a GG triode, the RF arc will hit either the chassis if the arc is
>> external, or the control grid if the arc is internal. An external arc
>> to
>> chassis probably won't harm the tube, but an interna arc to the grid
>> certainly can.
>>
>> The so-called "glitch resistor" in the B+ supply is a vital part of
>> every tube amplifier, because it limits the peak current: it's simply
>> Ipk=V/R. This resistor is not intended as any kind of fuse - it simply
>> limits the maximum possible current for a few vital milliseconds,
>> until
>> something *else* has time to switch off. Eimac Bulletin 17 covers this
>> very adequately.
>>
>> If the power supply provides adequate over-current protection for the
>> screen and anode supplies, and adequate over-voltage protection for
>> the
>> screen bypass capacitor, then arc faults due to loss of load can be
>> completely recoverable. Re-connect the load, press the RESET button
>> and
>> the amp will come back online.
>>
>> 2. Bugs in the tube chimney. Don't ask me how they got in there, but
>> in
>> FD situations I have sometimes found an earwig or a moth bridging the
>> anode and the screen. Again there's an arc and the amp trips out, but
>> this time it won't come back online until the charred corpse has been
>> removed.
>>
>> 3. Internal arcs due to gas release. I know that Rich doesn't like to
>> accept this; but I go along with the vast majority of tube
>> manufacturers
>> and professional RF engineers who have seen enough evidence to know
>> that
>> it happens - so we protect against it. Again, these faults are usually
>> self-clearing, and the amp will come back online when the RESET button
>> is pressed.
>>
>> 4. Any other reason the amp may choose! The most important practical
>> point is to accept that amplifiers occasionally DO arc, so they need
>> some protection.
>>
>>
>>
>> --
>> 73 from Ian G/GM3SEK
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>
>
>
> Rich Measures, 805.386.3734, AG6K, www.somis.org
>
>
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>
Rich Measures, 805.386.3734, AG6K, www.somis.org
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