Hi Gerald,
I could use K1FO's design, but I already have a "nice" working unit. The K1FO
won't physically fit in my RF chamber ( well it might with a hammer), and I
just wanted to do something quick to get perhaps a few extra watts and a bit
more headroom for JT65B, and know that I have a replacement tube.
I've got a 2x3cpx800 started, but if I could get a new stripline shoehorned
into the existing amp, that would be great. It does sound like I have lots of
options.
Maybe I should just build a new strip and fire it up to see what happens?
Paul
----- Original Message -----
From: TexasRF@aol.com
To: kg7hf@comcast.net, amps@contesting.com
Sent: Fri, 06 Jan 2012 02:41:11 -0000 (UTC)
Subject: Re: [Amps] Stripline design
Hi Paul, the single tube design has less capacitance at the tube than the
dual tube design. The lower the capacitance at the tube anode, the more
inductance required to resonate. More inductance equates to a longer
stripline.
If you need more inductance, a narrower stripline will have a higher
impedance and that will cause more inductance for a given length.
Added C at the tuning flapper will also lower the resonant frequency just
as increased inductance does. But, that comes with a price of higher loaded Q
that translates to higher losses. More tuning C will involve closer spacing
between the stripline and tuning flapper. Closer spacing means more likely to
flashover. You can increase the width of the flapper to increase the C and
retain the wider spacing.
Lot's of design trade offs here!
73,
Gerald K5GW
In a message dated 1/5/2012 9:51:16 A.M. Central Standard Time,
kg7hf@comcast.net writes:
Hi
group,
NHY to all! I am working on an amplifier mod and
need some advice. I have a currently working 70cm stripline amp based on
the 3cx400A7 tube. As everyone knows, that tube is getting rare and
expensive. Since I have a few 3cpx800A7's around here, I thought it
might be a good fit to change to that tube, especially for the eme contest at
the end of the month.
Besides the obvious physical size and heater
voltage, there is a slight difference in cin and cpk, I'm not sure what that
will do. I've never found any design plans, but this stripline is 3.5" x
8.625" long. and the tube is 0.25" (tube center is 1.05" from end) from one
end.
To fit the 3cpx800, I would have to extend the
stripline 0.375" so the tube would still be connected making it 9.0"
long. You can see what I mean
here:
http://a4.sphotos.ak.fbcdn.net/hphotos-ak-ash4/388232_2684319340428_1029693354_32301613_317232212_n.jpg
Does
extending the "null" end of the stripline make any difference? What
effect would this have?
I dug up the K1FO single 3cx800A7 70cm stipline
documentation and it shows the stripline as being 3.5 x 9.6875",
unfortunately
I don't think that will fit in my deck without extra work. On the other
hand though, I looked at K1FO's 2x3cx800 stripline and it is 9.0" long, just
like mine would be. Any speculation on why K1FO single has a much longer
stripline than I do and why his two hole has the shorter one? My guess
is the tune flappers might be in different locations and that makes the
difference.
Thanks for the insight on this and 73,
Paul,
kg7hf
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