>Thanks to everyone who responded to my original request. As I suspected,
>most
>of the information received was not very useful, because it was too general.
>However, John K5PRO was kind enought o send me a FAX copy of the SV572 data
>sheet, which (as I requested) is REAL data. Unfortunately, the Svetlana
>website is currently not open (at least from my QTH) . With a valid data
>sheet in hand was able to study the tube in detail. It confirmed my
>suspicions about this tube.
>
>Despite its higher voltage and dissipation rating, this tube is identical to
>an 811A when operated in the 1-2KV plate voltage range. Many of the
>applications for this tube fall into this range - the familiar 1500-2000V
>4x811A desktop KW. My old 30L1 is exactly such a beast, and is what started
>this whole thing. Anyway, within that range the operating characteristics
>and
>interelectrode capacitances are virtually identical. Also, it is not
>possible
>to drive the tube hard enough to require that higher (160W) dissipation.
>Above about 600ma. the Gm starts to drop like a rock . Hence, my original
>statement that it quacks just like an 811A.
>
? As it should, the filament/cathode is the same, and so is the peak
emission.
>Here is the real world side of the story. Several years ago I resurrected
>an old 30L1, a typical 2KV '"4-holer".
? The 30L-1 is not typical in that it does not use a separate VHF
parasitic suppressor for each bottle. With new tubes, there have been
reports of fireworks.
>When I got it I immediately launched a
>series of serious modifications, including a brand shiny new set of SV572's.
>I remember how slick they looked with their shiny new glass,red printing and
>slim waists. I pulled the 811A's but could not bear to throw them away, so I
>filed tham away in the back of a drawer. They looked so "old world" that I
>actually felt sorry for them!
>
>It is now about 1.5yrs since the slim-jims went into action, and in that
>time
>50% of them (that sounds more serious than just saying 2 tubes) have died -
>both of open filaments.
? The prototype AL-811 amp that I saw had a problem with broken
filaments. With a VHF parasitic osc., there is usually much peak grid
current and a proportional EMF that is perpindicular to the filament.
This Force can apparently break the tungsten wire. Old tubes that are
low on emission and amplification seldom have surprises.
>In each case, guess who got their old jobs back.
>That's right, folks. The old brown beauties went back into the sockets and
>the plate current/output RF amps never dropped an iota.
>
>In all of this technical discussion, there is only one point that calls out
>to me for serious comment. That is, the published spec for max. DC plate
>voltage is 1500V (possibly 1800 if you want to invoke the old ICAS regime)
>In either case, those geniuses at Collins who designed this amplifier
>blatantly violated the mfrs published spec on this key component of the
>design. Typically, this is not done by engineers and companies with
>integrity, which I believe Collins has always had oodles of. This fact,
>along
>with the poor job they did with the power supply design, makes me wonder if
>maybe the drug era started a little earlier and at a different place than we
>have all been led to believe.
>
>Eric von Valtier K8LV
>
? 2 millennia ago, the drug of choice was ethanol.
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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