It is quite normal for an amplifier to show lower efficiency when it is run
at lower drive and output levels. As the drive is reduced, the class of
operation moves in the direction of class A and we know that class has low
efficiency.
The higher efficiency comes at high drive and plate/collector/drain
currents. These conditions move the class of operation in the direction of
class
B or C. These classes of operation are known for higher efficiency.
I have no input on the broken core other than it sounds like there must
have been a lot heating going on.
73,
Gerald K5GW
In a message dated 4/17/2010 8:56:26 A.M. Central Daylight Time,
tzitzikas_ee@yahoo.com writes:
i mesured the r.f power with digital power/swr meter and it was only 190 W
at 106VDC (6A current). The manufacter claims that at 500w output r.f
power, at 110vdc, the current is 13A. So, the efficiency is below 50%.
---------------------------------------------------------------------
http://tzitzikas.site90.net (tzitzikas site)
http://forum.tzitzikas.site90.net (tzitzikas forum)
---------------------------------------------------------------------
--- On Sat, 4/17/10, Ron Youvan <ka4inm@tampabay.rr.com> wrote:
From: Ron Youvan <ka4inm@tampabay.rr.com>
Subject: Re: [Amps] 160m mosfet linear amplifier problem with ferrite cores
To: "amps" <amps@contesting.com>
Date: Saturday, April 17, 2010, 6:24 AM
HI sasas asasas:
> Hi, I have constructed this linear amplifier 500w rms (2 kW pep) (50
Ohms) with 12 mosfet irfp360, http://tzitzikas.webs.com/linear500w.jpg for
160m band.
> When I gave 3 Watts of driving power, it gave to output only 190 W at
106VDC (6A current). Two radio amateurs who have construct this linear claim
tha it gives 500w
> r.f power at 110vdc.
I have been looking at this schematic all week. I don't get the "500w rms
- 2 kW PEP" thing,
that doesn't make sense to me. RMS isn't that different from average and
2 kW PEP is about the same
as average.
Also, 106 V. X 6 Amps. = 636 Watts at 50% efficiency TPO = 318 Watts is
all you should be looking
for. (at this drive level)
The device substitution has possibly reduced the amplifier's gain and
efficiency.
> But when I tried to give 4 watts of driving r.f power the ferrite Cores
(43 material)
> of transformer T3 broken! Which do you think is the problem??
First, type 43 is correct for the HF HAM bands, but I am not sure about
the top band.
You need to replace the broken core and test it "just for gain" (no more
than 2 Watts of drive) at 7
MHz then compare the gain on 160 m.
> http://tzitzikas.webs.com/linear20a.JPG
> http://tzitzikas.webs.com/ferrite_broken1.JPG
> http://tzitzikas.webs.com/ferrite_broken2.JPG
Yup, broke.
--
Ron KA4INM - The next election, I know what is going to happen, I'm going
to help.
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