--------- Begin forwarded message ----------
From: km1h
To: sm3mxr@swipnet.se
Subject: Re: [AMPS] Highly efficient 813:s // 3CX3000 ?
To: <amps@contesting.com>
Date: Sun, 20 Apr 1997 10:45:52 PST
Message-ID: <19970420.104826.9671.3.km1h@juno.com>
References: <Chameleon.970420123700.EINAR@ast-7302>
Hi Einar.
First let me apologize for the "moron" statement as I was not aware
anyone on this list was using 813's! My comments were referring to
discourses on another reflector about the poor IMD performance, in SSB
service, of tubes that were designed for AM Class C service.
>From the owner/users standpoint RF is RF and IMD performance is usually
not of personal concern. Heck, in an SSB pileup even an old Galaxy 2000
amp (-16db 3rd order) would not be noticeable. It is when poor performing
amps are used in general ragchews and the like that they become
objectionable to those on neighboring frequencies.
The 3CX3000A7 is popular since it is one of the cleanest tubes ever
produced. At rated output the 3rd order products are spec'd at -52dB. It
is also a cheap tube to buy since it is often available surplus and the
Svetlana version is cheaper than an Eimac 8877.
Many industrial and medical RF amps use this tube and surplus equipment
is often available very cheap...they make for very nice conversions to
ham bands.
Yes, it takes a lot of drive power for 8KW but 100W will produce 1500W
with ease. The FT1000D and other 150-200W transceivers make popular
drivers.
It also has a 225W grid structure making it almost indestructible.
Hams in the USA are still afraid of tubes with more than one grid. Chalk
it up to some bad experiences 20-30 years ago and also excellent
marketing propaganda by Eimac. As Svetlana products gain more prominence
I am sure that tetrodes will experience an upsurge. With todays
technology it is absolutely no problem to provide the extra voltages
required.
Svetlana has also announced at the NAB convention that they will be
producing the 8874 and 3CX800A7 along with a 3-500z (3-600), later this
year or early 1998.
Now, if some company could produce a tetrode that is capable of some real
RF, IMD in excess of -30dB and lack of fragility, they would have a
winner. Most of us cant destroy a 3CX3000 but it is easy to wipe out a
pair of 4CX1500's in the blink of an eye....just ask ON4UN! The
Svetlana 4CX1600B is just as fragile; I certainly wouldnt touch a tube
with a 100 milliwatt grid rating. Protection circuitry is either
excessively complicated or far from bullet-proof.
73....Carl KM1H
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