Second Edition:
... ...
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>IMHO, thousands of good amps in daily use testify to Tom's credentials as
>a competent designer. I don't agree with everything he says and it makes
>me uncomfortable when exchanges get nasty ...snip...
Indeed, but you gotta admit that the helper who allegedly licks more than
envelopes story did liven things up a bit after the Rauchian camp ran low
on techno-ammo.
>On the other hand, IMHO...
Humble?
> RIch often gives the strong impression that he
>thinks no amplifier designer other than himself has any clue how to
>suppress/avoid VHF parasitics. He seems to imply, if not stating it
outright, that every
>commercial amp has parasitics and that they're killing tubes enmass.
Most of the ruckus has come from people who claim they only design
amplifiers that never ever have VHF parasitic oscillations.
- Suppressing VHF parasitics is neither esoteric or the exclusive
bailiwick of amplifier 'experts'. . The basics:
1. Place the tune-C close to the anode -- even if doing so messes up the
compliment-generating beauteous symmeticity of the front panel layout.
2. Reduce the VHF-Q / VHF-Rp of the anode resonant circuit -- even if it
adds 1% power loss on 10m.
There are two methods of accomplishing #2. Resistance-wire is not
superior to silver or copper, it only makes the job easier for Rs. {see
page 72 of the 1926 Edition of *The Radio Amateur Handbook* - - also, see
the {AMPS] archive}
My impression is that Mr. Rauch currently knows how to suppress VHF
parasitics. To his credit, Mr. Rauch has taken apart and inspected the
gold melt-balls in at least two tubes that failed from gold-sputtering.
My impression is that Mr. Erhorn sees things pretty-much in black and
white instead of shades of gray. Even though none of my articles
suggested that VHF parasitics are "killing tubes enmass", this is
apparently what he would like for those who have not read the articles to
accept as fact. .
>He seems to imply, if not stating it
>outright, that every commercial amp has parasitics and that they're
>killing tubes enmass. He might lead you to think it's the greatest issue
>in RF engineering. That just ain't so.
>
- The problem seems to be that Mr. Erhorn can not accept the evidence
that Mr. Murphy was right ("Things are more complicated than they
look."), that Forrest Gump was right ("Shit happens."), and that Richard
W. Erhorn is human -- just like most of the members of the [AMPS]
mailing-list.
- All but one of the HF amplifiers I ever built had marginal VHF
stability. The exception was the last amplifier I built -- a 4CX3000A,
in Class AB1 grid-driven service. . . And who knows, with the right
current transient, someday it could have a VHF parasitic oscillation at
its anode-resonance of 68MHz.
>Sure, some sloppily-designed amps have been produced by engineering-
>and/or ethics-challenged companies in the past. ...
Is it ethical to blame Eimac for tube failures that are due to
gold-sputtering?
> ... ... I know of no credible evidence of VHF parasitics in
>any Alpha ever built ...snip...
- I know that most Alphas do not oscillate. However, I have looked at
enough kaput 8874s, et cetera to know that some do. A photograph a tube
that was gold-sputtered in an Alpha amplifier appears in "Parasitics
Revisited" -- in the Sept 1990 issue of *QST*. However, QST decided not
to state which parasitic-damaged parts shown in the photographs came from
which model of amplifier. IMO, if George Grammer, W1DF, had been the
Technical Editor of QST in 1990, the manufacturers' names would have
appeared in the article -- Dick and Tom would have bounced off the
ceiling, and the matter would have probably been settled in a few months.
IMO, Grammer was the most technoblater-resistant person QST ever had on
it's staff. . Another such person was Rus Healy, who bailed out. .
. When I could smell trouble brewing over the VHF parasitics
controversy in early 1994, I wrote a letter to QST-Editor Mark Wilson,
suggesting that the ARRL Lab had the needed test equipment to make the
measurements that would settle the controversy. However, Mark Wilson did
not perform the needed measurements. Thanks to Wes, N7WS, the needed
measurements were finally made in December 1996.
Granted, more SB-220s, PT-2500s, 3K-As, and TL-922s oscillate than Alpha
77s, 78s and 264s and Ameritron-MFJ AL-80s -- but they all appear to
oscillate on occasion.
.........
"I know that most men, including those who are at ease with problems of
the greatest complexity, can seldom accept even the simplest and most
obvious truth if it be such as would oblige them to admit the falsity of
conclusions which they had delighted in explaining to colleagues, which
they had proudly taught to others, and which they had woven, thread by
thread, into the fabric of their lives." - Leo Tolstoy, UC1FAK
..................
Rich...
R. L. Measures, 805-386-3734, AG6K
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