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.
Here is the real world side of the story. Several years ago I resurrected an
old 30L1, a typical 2KV '"4-holer". 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. 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
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