Hi Will,
I'm still not sure I understand fully. I'll try one last
time.
Will replied:
>>> Again, no tube manufacturer ever gave warranties for
>>> sweep tubes in amplifiers (except GE). Every OEM bought
>>> from CECO or Richardson at one time, and the only
>>> warranties were given by the amplifier manufacturers
>>> themselves. At that, most amp manufacturers gave no
>>> warranties on sweep tubes. The M-2057, and 8950 are an
>>> exception as long as they were ran under the maximum
>>> design limits (design-maximum values). Those limits are
>>> what I posted earlier. These two sweep type tubes were
>>> the only two that GE specified as RF amplifier output
>>> tubes. Those are the only two I used besides
>>> experimenting with the Svetlana EL509.
> Watch what is quoted as some here have saved the posts. I
> said "I would have been fired" for designing something
> outside the limits of a specification, not anyone else. I
> can tell you also that an inside engineer can tell you
> anything, and if you don't have it in writing, the
> manufacturer can surely back out on a warranty if they
> want to. The comparisons about someone losing a license
> concerned only myself (being fired) or an example about an
> engineer causing bodily harm or death of an end user
> because of faulty equipment. If a law suit begins, and
> something is designed past its stated maximums, the
> engineer can be held liable for it. Any engineer can tell
> you this. If they are the engineer in charge, they are
> responsible liability wise. The only out is to have a
> letter from the parts manufacturer giving a go-ahead for
> one particular use.
> 900 Vdc is the design-maximum by GE, I'm not quoting RCA.
> Read the GE sheets and you'll see the difference. Most
> sweep tube curves don't show the design-maximum anode
> voltage. They stop about 1/2 way or a little below.>>>
As I understand your answer, because the sweep tubes have no
warranty it doesn't really matter how you run them even for
long periods of time. If a tube has a warranty, momentarily
operating outside data sheet maximum CCS operating specs
during tuning and adjustments is very bad engineering. On
the other hand, if the tube has no warranty it is acceptable
engineering to operate outside specs.
This is despite the fact that thoriated tungsten directly
heated tubes like 3-500Z's are not life-sensitive to
excessive anode voltage or emission current.
As I also understand, in the case of sweep tubes, which have
metal oxide cathodes, there is no splatter or short term
problems when you operate outside published curves. With a
3-500Z, it just won't work to do the very same thing.
This is despite the fact metal oxide indirectly heated
cathode tubes are damaged by excessive anode voltage and
excessive emission even for short periods of time.
Is my understanding correct?
By the way, you might want to think about this. As Rich
says, for a given output power reducing HV generally does
not make an amplifier cleaner. The exception to this is when
reducing HV increases negative feedback. Since the output of
a GG amp is in series with the input, negative feedback (and
gain) is an almost direct function of anode load impedance.
There are two ways to increase negative feedback. One is to
reduce anode voltage, and optimize energy transfer to the
load at reduced voltage. The second way is to overtune the
amplifier and then reduce drive.
If we don't reduce HV and overload to the same load
impedance, the amplifier is generally cleaner.
This is important to know if we want to tune amplifiers for
the cleanest signal.
1.) Reducing anode impedance increases negative feedback in
a GG amplifier
2.) Running the highest possible voltage for a given output
generally increases both efficiency and IM performance, all
other things equal.
It isn't correct to assume less HV results in improved IM
performance.
73 Tom
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