That '5106 is probably for Cable TV use and likely cuts off around 40 MHz
(on the low end!).
If I recall correctly, some of the general purpose units that go down to a
MHz use numbers from CA28XX group. They come in both single ended and
I've seen a few of the 350J's for sale on the web over the years. I don't
believe the demand is very high for those as they have a 26V heater and as such
can't be dropped into a 4CX250B socket. There is also the 4CX600J/JA/JB.
The 6146 shown on the Hughes schematic is run deep into Class A. Note the
low screen & plate voltages. I bet the numbers were just fine running all of a
For feed forward, an error amp with perhaps another 4CX350FJ would be
necessary. It is not a difficult scheme to implement but, it would double the
parts count for the project. If you read about the technique on the web, keep
in mind that "they" are typically working with transistor amps that start with
distortion numbers 20dB worse than tubes. Therefore, in this case, less
correction power will be required, the output combiner ratio will optimally be
a bit higher, and power lost from the main amp will be lower.
The subject line said you wanted "the Cleanest Linear". To avoid
degrading the system, the driver should exhibit distortion specs at least 10dB
better than the amplifier. Your FT-1K will still be useful for the receiver.
73 & Good morning,
-- "Tom Cathey" <K1JJ@comcast.net> wrote:
Now THAT'S the kind of info I've been looking for, OM.
OK on using the 'J' tube versions and the TRW class A chips. I imagine the
J's are harder to find used.
I went to a site that has a CA5106 TRW RF Broadband stick... is this the
Here's the link - they have lots of interesting low level RF chips:
Your website schemtic of the amplifier with negative feedback is quite
helpful. I can see where they neutralize each stage, grid driven, and see
the simple neg feedback from the final to the driver using a 20pf cap from
plate to the driver cathode. Though, I didn't see any feedback for the pre
driver, the 6146. I guess this amplifier was is just for an example since
the 6146 w/o feedback is not that clean, I understand. I don't think this
will be too hard to pull off using other tubes and these basic techniques.
I just did some reading about adaptive feed forward systems that you
mentioned can approach -80db 3rd order IMD. They talk about cancellors. I'm
not sure if I should persue that - might be too complex for the job. Then,
as you said, the FT-1000D even at the low level 10mW tap, would not be a
good driver for this super clean system.. The homebrew ssb generator is
intriguing. I do have experience constructing SS stuff, but wonder how much
of the FT-1000D I would retain as a unit with this outboard stuff. I think
the 10mW FT-1000D output with simple negative feedback in the linear might
be all I need to grab another -15 to-20db IMD over the 3-500Z amps. That's
what I'm looking for.
Thanks again, Marv.
Well, you have a certainly started a string here.
A couple of suggestions for you.
Use the 4CX350FJ. May as well start with the lowest distortion.
Don't try to employ RF feedback across more than two stages.
Use one of the old TRW - Motorola - M/ACom class A bricks for the first
Since you are operating narrowband, consider the feed forward
configuration. If you start with a -50dB distortion amp, you should be able
to slice another 30dB off that figure for a -80dB system.
I doubt if your exciter, at any level, is clean enough to drive the above
Fortunately, a clean 80M SSB generator is easy to construct compared to
the balance of this undertaking.
73 & Good afternoon,
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