[Amps] AL-80B questions

[on4kj]

Hello,

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