[Amps] AL-80B questions

[2]

>Hello,
>
>a.k.a., NIH syndrome...
>What kind of a illness is it?

**  Not Invented Here Syndrome is mostly a corporate disease.  No 
manufacturer likes to admit error, so there's a tendency to blame others. 
 For example, ETO used to build MRI amplifiers for GE Medical .  
Eventually, GE discovered that there was a high rate of 8877 tube 
failure.  GE reportedly told ETO to fix the problem.  ETO blamed Eimac.  
GE cancelled ETO's contract.  As I see it, improving 8877 stability would 
have cost c. $4 in parts and about 2% in P output.  [note - Eimac was 
easy to blame since their warranty replaces All kaput tubes except those 
that were obviously dropped on  a concrete floor]

cheers, Jon

>There is still something to learn, even if it is not Amp. related. You never
>know.........
>Thanks.
>Jos ON4KJ
>
>
>
>----- Original Message -----
>From: "2" <2 at vc.net>
>To: "Tom Rauch" <w8ji at contesting.com>; " AMPS" <amps at contesting.com>
>Sent: Sunday, March 02, 2003 6:37 PM
>Subject: Re: [Amps] AL-80B questions
>
>
>>
>>
>> >> >Rich, maybe you can put aside all the innuendo and diversion and
>explain
>> >how
>> >> >a parasitic can mechanically displace a filament, while thermal
>cycling
>> >or
>> >> >material problems are not likely to do so.
>> >>
>> >> Both apparently can.  Eimac cautions against having more than c,
>29A-rms
>> >> of filament inrush current - presumably to avoid distorting the
>filament
>> >> helices.
>> >
>> >Eimac states that as a general rule, and it is very conservative.
>> >
>> **  The Eimac 3-500Z spec sheet says neither.
>>
>> >The problem arises when the tube has poor materials, or is improperly
>> >manufactured.
>>
>> **  a.k.a., NIH syndrome.
>>
>> >The AL80 series has a very long history with good tube life.
>> >This filament-grid issue really just started when Amperex tubes were
>used.
>>
>> **  I sell parasitic suppressor retrofit-kits to AL-80 owners who tell me
>> they had an Eimac 3-500Z short.
>>
>> >It appears even in amplifers that have a LONG field history of no
>failures,
>> >when Amperex tubes are used as a replacement.
>> >
>> **  Passing the buck.
>>
>> >For example, I have an AL80A that was used with an Eimac tube since 1983.
>I
>> >changed that tube last year to an Amperex, and it failed G-K within a
>week!
>> >A replacement lasted about six months, and failed the same way again. A
>> >change to one more Amperex tube and the amp has run even since.
>> >
>> **  not all 3-500Zs have the same vhf gain.
>>
>> >> I have autopsied a number of grid-fil shorted 3-500Zs that were
>> >> funtioning normally before their grid choke imploded, and/or the grid-I
>> >> meter and/or shunt exoloded, and/or the vhf parasitic suppressor
>resistor
>> >> more than doubled in resistance without showing external signs of
>> >> heating.  (tubes removed from amplifiers that had c. 60% of 29A of
>> >> inrush).
>> >
>> >Carbon resistors age with time and heat. They are notorious for that. But
>> >then I'm sure you know (and choose to ignore) that fact, so I won't
>rehash
>> >the same old facts of life you choose to reject.
>> >
>> **  I agree that carbon comp resistors age, but I have not seen a change
>> of more than 30% in either 5% or 10% tolerance units c. 20-years old.
>> With what seem to be vhf parasitics, I see 400% changes in newly replaced
>> units.
>>
>> >> -  A friend took his SB-220 to work, coupled the anodes to a spectrum
>> >> analyzer, and found there was damped-wave ringing at c. 110MHz at the
>> >> anodes when sending 50wpm dits, even though grid current was normal -
>> >> thus, no vhf oscillation was present.
>> >
>> >I doubt it.
>>
>> **  He told me he put a probe near the anodes and had a look with a
>> spectrum analyzer.
>>
>> >In order to have damped wave "ringing", there must be a
>> >transient with a response slope much more rapid than the frequency of
>> >ringing,
>>
>> **  So you are suggesting that a spark transmitter could not produce RF
>> at a higher frequency than that of it's rotary spark ?  Give us a break,
>> Tom.
>> >
>> >Even if there were ringing, which I doubt,
>>
>> **  The long excursion on the wide river in the Land of the Pharoahs
>> continues.
>>
>> >it goes nowhere towards proving
>> >anything except the amplifer is stable. If it were  not stable, it would
>> >oscillate.
>>
>> **  On occasion it apparently had - which is why he took the SB-220 to
>> work and took a  look with a spectrum analyzer.
>> >
>> >Many or most people don't know how to use spectrum analyzers properly,
>and
>> >that could 9or could not) be the root of what he thought he saw. If you
>> >collect enough data and disgard what you don't like, you will eventually
>> >have something to support your wild theories Rich!
>>
>> **  Except for those in denial, spark transmitters are an undeniable part
>> of history.
>> >
>> >> was a feedback path between the SB-220's anode output and cathode
>input.
>> >> Unfortunately, there is 0.3pF of feedback C.  At 110MHz, 0.3pf = c.
>> >> 4800-ohms of XC.  This doesn't seem like much until one discovers that
>> >> the length of RG-58/U coax used at the cathode input of the SB-220 is
>> >> resonant c. 110MHz.
>> >
>> >First, the .3pF was taken as an equivalent at 30MHz, not 110MHz.
>>
>> **  Not the case.  Eimac describes the method used.
>>
>> >The peak in
>> >effective feed through occurs around 200MHz, when grids are grounded
>> >properly.
>> >
>> **  Tom does not believe inductively-coupled dipmeters.
>>
>> >Second, the length of cables mean little or nothing by themselves. It is
>a
>> >complex circuit, with stray capacitances and inductances as well as the
>> >input circuit itself part of the system. If you sweep the input of the
>tube
>> >you will find the VHF impedance at the cathode is low.
>> >
>> ** The problem is that the RG-58's resonance isolates the cathode from
>> the low-pass (110MHz attenuating) tuned input.
>>
>> >The length of cable between by dummy load and amplifer is 1/4 wl at 21
>MHz
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>
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-  R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K, 
www.vcnet.com/measures.  
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