[Amps] AL-80B questions

Sun Mar 2 23:50:23 EST 2003

Thanks Jon,

This will help a 68 years young pupil  to have a better understanding when
reading texts.

----- Original Message -----
From: "2" <2 at vc.net>
To: "on4kj" <on4kj at skynet.be>; " AMPS" <amps at contesting.com>
Sent: Sunday, March 02, 2003 10:40 PM
Subject: Re: [Amps] AL-80B questions

>
>
> >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
> >> _______________________________________________
> >> Amps mailing list
> >> Amps at contesting.com
> >> http://lists.contesting.com/mailman/listinfo/amps
> >>
> >>
> >
> >
> >_______________________________________________
> >Amps mailing list
> >Amps at contesting.com
> >http://lists.contesting.com/mailman/listinfo/amps
> >
>
>
> -  R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
> www.vcnet.com/measures.
> end
>
>
>