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Ok P
Well I just looked at a pic of the amp
, tubes are 811a replacements , good tube ,
in grounded grid ? , 813 has similar anode
dissipation 120 watts , but more gain +
neutralisation problems : ( ....... 4cx250 in free fall
must of been a spectacular event , touch wideband ! I
lost x 3 807 when the bias failed ,
looked like snow storms inside the tubes before
they burst , funny non of the fuses popped , only
the main one in the the house ......introduction to transients
.. 1 MW Klystron , yes , most think they are
little things like local oscillators hihi, what
no noise , 'scope-dope' seems to ring a bell ....
New radar systems , data processing, digital processing
of radar data has been in place for
a very long time... after H2S , not very much is
published about AI ....
Good luck with the build projects , Im just slowly
acquiring a shack full of broken equipment as things
start to fail due to age , , the racal syncal-30 is
the latest to develop a sense of humour, with
distorted tx audio , first time it was
used /P in the Isle of Man last week ..
G..
Don't see any problem with the BS reflector, any
attempt to define what is 'topic' is
in these advancing days is perhaps a little
blinkered ,
Sent: Thursday, June 14, 2012 10:24 AM
Subject: Re: LF: RE: Class E etc
Hi Again Graham
The FL2000b has 2 x 572B triodes in parallel grounded grid. These are
directly heated tubes and have carbon anodes. 1/ they give a good light display
and 2/ you can tune up by observing the "blush" on the anodes (if you wanted
to). I have had it years hardly use it got after the original owner had had it
retubed and serviced. Makes a bit of difference on 80m when the going gets
difficult.
As with your hipower thyratron all you need is a good multi Kw PSU.
Oh and some x-ray protection?
I spent a bit of time in the MoD back in the 90s and one radar I used
to visit was on Scotland's east coast it was very old
but nothing to replace it. The whole transmitter cabin rotated with the antenna.
God knows what the power O/P was. The power pickup was via a pair of circular
channels of mercury and the bottles in the cabin where a sight to see probably
kicked out as much x-ray as they did microwave.
We were running a mobile radar fairly modern still thermionic had a
massive single Klystron 1MW pulse! On site was a new solid state phased array
unit there to replace the old rotary cabin Joby but wasn't having a happy time. A major
complaint was the ops couldn't turn the
rx gain up to see the sparkles to be confident it was working..... hee! The new
systems have a lot of software processing before the display reaches the scopie.
Hasen to add I am not a radar expert in any way. When you work for that outfit
you get thrown into jobs you know nothing about. I was mainly on comms
infrastructure and didn't know much about that either.... ;-0.
Oh and yes used 4cx250s and 4cx150 in 2m and 70cms PAs the one for 70
took off and recked my transverter. They were designs out of the old RSGB VHF
handbook when I were a Jaite!
I am not going back to Hi power Tube rigs again its not necessary when hi
power FETs are so cheap.
Any way this all a bit off topic. Its bit like the last day at school
before the summer break on this reflector doing what you like before it gets
turned off.... hee! And not much to do with Class d/e or any other letter of the
alphabet.. What I have to sort out is my RX for MF/LF it is not good, need some
ideas?
73 es GL Pete M0FMT IO91UX
This is what you need (with a bit of re-work)
.....
VK or Bust !!
FL2000 , with 2 x 813 ? nice
amp, my skanti trp5000 has
2 x 4cx250-b in the PA runs well
1.8/30 Mhz , I use 2
combined skanti 250 watt solid state 50v linear amps
with the ma1723 for LF>Hf , wide band ,
just change the ATU hi ..... could do
with a simple class e/d for 500 as the
ab1 amps are a little power hungry ..
G..
Sent: Wednesday, June 13, 2012 11:59 PM
Subject: Re: LF: RE: Class E etc
Hi Stefan and Graham
Thanks for the comments. None of my MF/LF tx.s run more that 160watts although by seriesing a couple of
PSUs one with a
floating ground I can run about 280Watts o/p from the TX. I don't like seriesing the PSUs so only do it during
experimenting not on the air. Need to build a new high voltage PSU 100V at a good current
rating. The rigs are FET PA IRF840 etc mostly xtal controlled or xtal mixer type master
oscillator (but do have DDS), into a FET driver chip. And set them as described
earlier.
I have played with High power Audio amps on 136kc/s transforming the
Low impedance to 50 ohms+/- using Ferrite cored transformer to drive the antenna
tuner. Front end currently popped!! Using it for QRSS overnight.Will get
it back on soon.
My interest in Valve or Tube TX is a side issue and am not advocating
them for serious modern MF/LF work. However there is no reason why
not.
I have made a couple of TUBE QRP rigs one for 160/80 about 4/5 watts out Choke
modulated AM and CW and FSK. Worked most of UK on AM on 3.615megs. The
second is a copy for 500kc/s was originally VFO controlled but now is again xtal mixer vxo. They use 6CL6 video
tubes in the PA. The 500kc/s tube tx only runs a watt o/p yet to figure out why, it
should be about 5watts. How ever on my new found Opera4 have been
reported in PA0 land (on the limit).
I have built and still got one or two 807 PAed rigs for 80m
knocking about. Plus a Louis Varney design made by an unknown amateur in the
1950s and a Codar
T5 and a push pull 807 rig on the stocks.... but probably won't get finished.
Plus an FL2000B. This to show my thermionic credentials.... hee!
For shear interest I would like to try and make a high efficiency
TUBE PA but probably won't get around to it. But that 1960s RCA AM BC TX design
looks interesting but probably very dodgy to set up, stability and all. Graham
your arc tubes is all very well but what I have read is that they have a
tendency to blow up...... and so do FETs ok so no change there then.
My current limitation to power Stefan is lack of a single stable
PSU with a couple
of KW output. The antenna is now reduce to 35ft up and 128ft top.
I don't have a good RX for MF/LF what I have are deaf by others standards and
this is my main area of interest at the moment. I have used a TS50 and a TS690s
full filters plus a couple of direct conversion HB RX with
active filers and notch.
Front ends have gone from dual gate mosfet to straight into the mixer but S/N is still
poor evidenced by WSPR and Opera reports I
give to other station who are being received much better elsewhere. If
any one can help me with that then it would make life here on MF/LF a lot better.
Keep the bands
open and may get to work you Stefan now you have 472/9....... why the delay in the UK????
73 es GL Pete
M0FMT IO91 UX
Hi Pete, LF, On 137 kHz or 500 kHz you can quite easy achieve 95%
efficiency with a class E PA. BTW a ferrite transformer is not needed! So if
your antenna provides stable resonance and impdedance and if you like to play arround a bit to obtain
the best efficiency (not the highes output power), a well designed class E PA is
definitifely a good
choice! 1 kW RF (CW, key down!) is possible with a single IRFP MOSFET. I hardly
expect that you will get such an efficiency with a tube amp but i can understand
the fascination of a glowing tube in a dark shack, although i'm not from the tube
generation ;-) The first power amplifier i heard of was a 2N3055 in the late 80s
as i was 12 year old or so :-) 73, Stefan/ DK7 FCAm 13.06.2012 16:51, schrieb M0FMT:
Well shoot me down with my
britches on fire!
Mal
I have just found an article on an enhanced Class C in Tube
amplifiers By RCA.
I have heard of higher efficiency
Valve amps but never gave them any time because I thought they used special
valves to achieve the fast response. But apparently not, it relies on a tuned
circuit in the anode and cathode. The cathode LC being set at the third
harmonic of the anode one. By combining the drive wave with the third hamonic you get a very
fast rising pulse type wave at the drive frequency in the PA tuned
circuit as with a class D/E solid state amp. URL is ........ http://nrcdxas.org/articles/bta5t/
I think the point about this is
that it works OK for fixed frequency TX's like broadcast transmitters and the like.
And probably will work OK for us on LF with such narrow allocations where we
may get away with one set up.
Now to see if it is scalable to
lower power video tubes.
73 es GL Pete M0FMT IO91 UX
Pete es Co
The class C tube amplifer is the nearest you can get to class D or
E and well designed would produce 70% efficiency.
The class D or E is not really an amplifier in the convential sense it is
merely an RF switch at the frequency of interest and the voltage generated is
increased by a step up transformer with probably 80% to 90% efficiency if you
are lucky.
Like some have said a tube amp is more robust and
tolerant of mismatch to antenna without smoke. Fets are good but can go bang if one is not
careful about matching to load.
I have some Dentron amps for the HF bands and they have been
going for years.
Fets are probably more manageable, compact
and safer regarding voltages, beware of tubes with voltages of a few
K/volts at high current, like an electric chair!!
73 de mal/g3kev
----- Original Message -----
Sent: Tuesday, June 12, 2012 11:15
AM
Subject: Re: LF: RE: Class E etc
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
IO91 UX
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
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 a good practical circuit for a single ended
amp that is a scalable surefire
design, no need to reinvent the wheel.
For antennas and antenna feed methods a "look no
where else site"
73 es GL Pete M0FMT IO91UX
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