Manfred,
I was told that some of the high power devices have such a small footprint
for their cooling that air cooling is not suitable. For the 100 watts per
device, air cooling should be OK. I wanted to be sure. The cold plate is made
by Lytron and they can be googled. The cold plate I ordered/recieved is
probably twice the size I need to get the job done so I have room for all the
modules, no problem. I want to be able to use this linear 100 percent duty
cycle in a room without air conditioning if necessary.
The IXZ2210N50L is suitable for HF linear service and is the device that I
would like to use due to the low cost and availability. I would like to
collaborate with you on this project and have purchased most items already
except the actual RF devices. I also have spent time on the bandpass filters
as well. Due to the high power expected at 1KW plus, I have purchased enough
Russian vacuum relays to cover all the filters. I suspect the IXZ2210N50L is
suitable for 6 meters as well and was considering using the 54mhz low pass
filter out of the QST article that uses copper plate inside the project box. I
have purchased/received some TELCOM switchers that are pretty high quality and
plan to use 100v power supply. Their website has changed since I started to get
all the parts but origionally had a schematic for an HF module with the
IXZ210N50L. It is no longer on the website and I have it saved to a different
computer that has some problems on it right now. When I
remove the hard drive and slave it I should be able to pull the info off it
and send it. I have less than a month here and will be gone again for another
6 months at sea again so have a few weeks to do a little work on this project.
http://www.ixysrf.com/pdf/briefs/Linear_Z-MOS_PB.pdf
http://www.ixysrf.com/pdf/switch_mode/IXZ210N50L.pdf
73,
Mike
Manfred Mornhinweg <mmornhin@gmx.net> wrote:
Hi Mike,
> I have already worked out details for my liquid cooling scheme. I
> found a good source for a cold plate and recieved it.
I would be interested in where I can buy such a cold plate! I googled
for them, and found hundreds of models for CPUs and video chips, but
nothing large enough for the power level I need, much less if all that
heat comes from a few small spots!
I do have some machining ability, and a small lathe which I can
configure as a milling machine, but copper isn't an easy material to
work with, so if at all possible, I would prefer buying this piece
ready-made.
> I had a guy
> help me in USA (I am overseas in Japan) with adaptors. The reason
> why I need adaptors is because the water cooling pump that I ordered
> has different connections.
That would be no problem for me, thanks to the lathe. I can make
whatever custom adapters I might need.
> If you need details, I can provide some
> but it sounds as if your water cooling scheme is figured out.
Any help is welcome! All I have worked out so far is the basic equations
for heat transfer from the silicon to the water. I have not started
designing the cool plate. I think with the information I have now I can
safely design the cool plate, but information about any practical
example would be most useful, even if it is only to check the validity
of my formulae!
> I used
> a radiator that is close to what you would find on a car but is for
> industrial applications and was found on Ebay. The fan is 12vdc but
> is so powerful that the stainless steel blades are flatted out on it
> when power is connected.
I imagine how noisy it must be! Beware! I couldn't hear the DX! :-)
No, for my amp I don't want any radiator nor a fan. Eliminating fan
noise is the whole point of water cooling! I intend to use a simple
bucket of water under the desk. That has enough heat capacity for a
pretty long operating session, and can cool off naturally during the
non-operating time. If I feel generous, I might actually buy a water
container that has a lid!
In the meantime, I ran some design exercises. One was about a class AB
linear amplifier using 4 modules having each a pair of IXZ210N50L
MOSFETs in push pull. With power combiners and all the stuff. Very
conventional technology. It turns out that assuming a pretty good water
cooling system, this approach still falls a bit short of delivering
1.5kW safely in high duty cycle modes. For SSB it would be OK.
It seems that using the dual version of this MOSFET, or using two in
parallel on each side, can easily lead to power distribution problems.
Then I calculated a situation with just one pair of DE475-501N44A
MOSFETs in push pull, in class AB/C with envelope restoration. Class E
or F seems quite hard to do, because I don't want to have to tune the
amplifer! That's a detail I had not realized before... those classes are
so critical in the proper resonance, that tuning to the specific
frequency and with the specific antenna impedance is mandatory. Well, in
class AB/C with a modulated power supply I can develop 1.5kW in 100%
duty cycle with a single pair of MOSFETs, but the cold plate design (and
specially its making!) become rather difficult. The same project, but
using ARF1500 MOSFETs, is easier, because they are much larger.
All the above is assuming that the whole mounting surface of each
transistor is thermally active! I don't know how far that's from the
truth. The farther it is, the more difficult cooling becomes. And the
more difficult cooling is, the more useful it is to run class C or above!
I also passed the information I have to a good friend, who is not a ham,
but is pretty good at mathematically solving problems. I asked him to
look into the differential delay issue, and into the phase modulation
caused by the MOSFETs. Let's see what he comes up with! I'm pretty
confident that the distortion from differential delay is acceptable for
ham SSB use, but I really have no idea now how big the phase modulation
effect is.
I was thinking about making a small scaled down model amplifier, using a
pair of cheap small MOSFETs at 80 meters or so, running at perhaps 30
Watt output, and measure distortion there!
I just need time.
Cheers,
Manfred.
----------------------------
Visit my hobby website!
http://ludens.cl
----------------------------
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