Years ago, several ham friends of mine have made valve type
transmitters run in Class-D or E on 75 and 40 meters, 500kHz should be
no problem at all.
73 Warren K2ORS
On Tue, Jun 12, 2012 at 7:15 AM, M0FMT <[email protected]> wrote:
> Hi Ken
>
> I believe you can operate some thermionic devices in higher classes than
> C but they generally lack the frequency response of a modern FET. I won't go
> into figures but just think about it. The high efficiency output stage has
> to operate like a switch it is not actually an amplifier. The faster it
> changes state from fully on with ultra low resistance to fully off
> (which means a device that will operate well into the VHF) the higher the
> efficiency. If you have a device that is barely rated to say a couple of
> megs its not going to be much good (in terms of what we are talking
> about) at 500kc/s. Remember you are trying to get the magnetic field in the
> inductor to rise and collapse at a very fast rate in-order to generate a
> high electromagnetic field at the drive frequency. We are not talking sine
> waves here as a scope on the drain will show. Although a scope on the output
> side of the drain inductor will show quite a clean looking sine wave. Try
> it.
>
> That chart at the end of that PDF file is very clever and is the guide I use
> to bring a PA into optimum performance.
>
> What I was trying to say is that the math is all very well but if you are
> trying to make a practical and efficient CW TX for LF then there is enough
> empirical data from following the guide lines lines shown on the sites I
> have posted that will get you a good TX. If you want a doctorate in
> theoretical physics to bamboozle you colleagues then that will detract from
> the time it takes to build a very interesting high power, efficient TX
> design well within anybodies capabilities. The GW3UEP design being IMHO a
> very good (Scalable) example with no RadCom style unobtainium in the
> components listing.
>
> 73 es GL Pete M0FMT IO91UX
> From: Ken <[email protected]>
> To: [email protected]
> Sent: Monday, 11 June 2012, 22:09
> Subject: LF: RE: Class E etc
>
> Hi Pete.
> About 40 years ago my integration was quite good, liked doing 2nd order
> differential equations, partial integration and integration by parts, the
> one thing I had big problems with was 3 dimensional integration of a point
> in free space . Looking at some of the sites my Class C MOSFET PA is
> probably more like Class E by default. The reason I like valves is because
> they are very forgiving devices unlike semiconductors, also the keep the
> shack and the cat warm.
>
> 73s
>
> Ken
>
> M0KHW
>
> From: owner- [email protected] [mailto: owner-
> [email protected] ] On Behalf Of M0FMT
>
> Sent: 11 June 2012 19:16
> To: [email protected]
> Subject: LF: Class E etc
>
>
> Hi Ken
>
> Ha ha Stefan, how good is your Integration Ken?
>
> Here are a couple of sites that should answer your questions. You need a
> good dummy load and a good oscilloscope. Setting the conditions for the
> amplifier is to do with A/ the correct driver preferably using a FET drive
> chip (like TC4422 non and TC4421 inverting) that will turn the FET fully on
> and fully off on each cycle. Very fast rise time with accurate on off timing
> (mark / space). Ensuring the max permitted gate voltage for the FET is not
> exceeded otherwise they pop, look out for transients, a diode clamp helps.
> B/ Setting the shunt capacitance and inductance in the drain circuit can be
> done empirically See article below. Then follow it with a low pass filter,
> although the output wave will be surprisingly clean. Calculating the values
> is difficult as you don't necessarily know all the starting parameters and
> in any case the result is going to wide of the mark. The site below will
> gives some starting values. Best to use 'Scope measurements to set the
> output conditions. You are looking for fast, very fast On / Off rise times.
> Gate drive and understanding the drain circuit is the key.
> These amplifiers are capable of incredibly good efficiency well above a
> dodgy class C amp. This means the heat dissipation from the FET is very low
> at high power giving cool heat-sinks!
>
> The GW3UEP (do a web search) single ended design is capable good
> efficiency and high power depending upon the FET used and Drain supply
> voltage. I have modified one to run reliably at 140watts and is capable of
> almost twice that into a dummy load with a heat sink that is fairly cool.
> Adjusting L and C empirically using the 'scope to get the correct drain wave
> shape for max efficiency is the way to go. The article below shows you what
> you are looking for. I set my TX up into a 50 Ohm dummy load adjusting L and
> C to get the correct drain wave shape on the 'scope then measuring the peak
> voltage across the Dummy load. I then transfer my connector from the Dummy
> load to the input of the tuned transformer in the antenna up-lead. I adjust
> the coupling link to give the same peak voltage across the tuner link turns.
> You are not looking for maximum peak just the sames as across the dummy load
> indicating a 50ohm match. This is done by either adding or reducing the
> number of turns (about two turns) along with bringing the the transformer to
> resonance by measuring the peak up-lead current, here you are looking for
> the maximum peak.
>
> Oh yes and WIMA high voltage high value capacitors from Maplin work well.
>
> Read the articles and search info on class E amplifiers.
>
>
> For some bed time reading but ignor the math look at the Tuning Procedure
> and the pictures at the end which tell it all really.....
> http://www.cs.berkeley.edu/~culler/AIIT/papers/radio/Sokal%20AACD5-poweramps.pdf
>
> For design ideas
> http://www.classeradio.com/
>
> For a good practical circuit for a single ended amp that is a scalable
> surefire design, no need to reinvent the wheel.
> http://www.gw3uep.ukfsn.org/
>
> For antennas and antenna feed methods a "look no where else site"
> http://www.strobbe.eu/on7yd/136ant/
>
> 73 es GL Pete M0FMT IO91UX
>
>
>
--
73 Warren K2ORS
WD2XGJ
WD2XSH/23
WE2XEB/2
WE2XGR/1
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