[AMPS] CW amplifier progress (well, daydream progress) -- long

[Radiodan W7RF]

Michael J. Baker wrote:

> The 3CX800A7 and 3CX1200A7 are expensive and not instant-on.  Also they
have
> somewhat low grid dissipation ratings and I'm afraid of damaging them.
>

The 3CX800A7 is NOT instant on and has a 4 watt grid dissipation. $435ea.
from Radiodan.
I share your concerns about the above tube. The low grid dissipation rating
is one reason why amplifiers using them near maximum ratings are SO
sensitive to SWR. Better be flat or cut the power back.

However, the 3CX1200A7 IS instant on and has a rugged 50 watt grid. $625ea.
from Radiodan.
Everyday I very comfortably load my Henry 3K Premier (using a 3CX1200A7)
into my Force 12 C4XL antenna which has poor SWR on a portion of 40M (hi on
fone, tuned for CW) and 12M & 17M (these bands are throw in "freebies" with
3.5:1 SWR). I don't bother with a tuner here. Just load it right up, no
resetting "protection" circuits or backing off the power or duty cycle.

(I mention prices here for relative comparison)
Expense is relative. Probably the best pure dollar value tubes for 2000
watts or less are the 3-500C tubes of today ($250/pair from Radiodan).
Quality varies widely, buy from a trusted source. I would not pay extra for
NOS Eimac.

We sell the same 3-500C tubes as used in the Henry amps. We know this brand
works well.


73, Dan Magro W7RF, (President WARC 1999, member SCDXC, SCCC)
Manufacturers Rep & Distributor for HENRY RF Power Amplifiers.
www.radiodan.com <http://www.radiodan.com>     RFpower@radiodan.com
<mailto:RFpower@radiodan.com> A trip to our web site is worth the click!




> -----Original Message-----
> From: owner-amps@contesting.com [mailto:owner-amps@contesting.com]On
> Behalf Of Michael J. Baker
> Sent: Monday, March 15, 1999 3:28 PM
> To: <rakefet@rakefet.com>
> Subject: Re: [AMPS] CW amplifier progress (well, daydream progress) --
> long
>
>
>
> Vic Rosenthal wrote:
> >
> > Goal: 1200-1500 watts CW output, 160-10m.  Reliability under CW contest
> > conditions is the first priority.  Low cost is the second.
> >
> > Tubes:  I like the 8877, but pulls are getting hard to find and
> more expensive,
> > and I feel (wrongly?) more comfortable with new tubes.  New 8877's are
> > outrageously expensive.  I am thinking about a pair of
> 3-500Z's: they are
> > available, not too costly, rugged, and instant-on.  NOS Eimacs
> are available for
> > $330/pr and RF Parts has their own brand of Chinese tubes for
> $250/pr.  Any
> > comments on the RF Parts tubes?
> >
> > The 3CX800A7 and 3CX1200A7 are expensive and not instant-on.
> Also they have
> > somewhat low grid dissipation ratings and I'm afraid of damaging them.
> >
> 	Just a passing thought from a new guy to the reflector, but
> not new to
> homebrew amps.
> 	Why not consider either one or two 4CX800 by Svetlana?  Cost is
> reasonable at $190 each and the sockets are only $22 each.  Two tubes
> would loaf along at 1500 watts output and the design is nothing new.
> Both DownEast Microwave and, I think his name is Andy from England who
> posts to this reflector, have the boards for the necessary voltages and
> lots of protection for the tetrodes.  Nice stuff.  You could drive the
> pair with (a guess here, ok, please dont flame me, ask andy) about 40 to
> 50 watts and get full output reducing the load on the exciter so
> contesting should be no problem.
> 	I am looking seriously at doing just what I have suggested
> myself and
> making a good, solid, reliable amp with thoes bias boards and using the
> methods described by Rich Measures on his home pages about the QSK
> system.  For us CW guys, what could be better?  New tubes with a
> warranty, guys who have already done most of the homework for us, and a
> proven design that won't cost you $2500.  I figure with what I have
> already collected and spent, even with the new tubes I should be able to
> get it built for under a grand.  Not bad when you consider what you get
> used for that money.  NO QSK, NO warc bands, and older ageing
> componenets.  BUILD IT, IT WILL BE FUN AND A LEARNING EXPERIANCE, AND IT
> WILL SAVE YOU ABOUT HALF THE COST OF A NEW ONE.
> 	(Just my 2 cents worth.  Your mileage may vary.  Title, tax
> and dealer
> prep not included.)
> 	Good luck with the project and keep us folks on the
> reflector posted as
> to your progress.
> 	Nothing smells as good as sucess..
> 	Best 73,
> 	Mike Baker K0QZ, Phoenix (proof God does have a sense of humor.)
> >
> > --
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>
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>


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