On 8/24/2011 3:18 PM, Manfred Mornhinweg wrote:
> Roger,
>
>> Agreed. I use Artic Silver when I can not solder.
> That's good. I would like to buy some Arctic Silver, but need to find a
> store that will sell me a small amount, and export it! Here in Chile, of
> course, that stuff is unobtainable from the local distributors. I can
Are you any where near Santiago?
Are there import duties on things like Artic Silver?
> easily get the usual white ceramic thermal compound, packaged in little
> jars with no label, so I don't know what's really inside!
it's more than likely the standard silicone heat sink compound. Probably
SiO2 (Silicone dioxide and a binder such as a high viscosity 200 fluid)
> And with
> ceramic thermal compound ranging from 0.7 to 3.8 W/mK in thermal
> conductivity, I would like to know what I have... So I guess that I will
> include a small jar of labeled, specified thermal compound in my next
> order from Digikey, but that's still only 3.something thermal
> conductivity, while Arctic Silver is rated at 8.something. Digikey has a
> silver loaded thermal compound too, but with no specs. Any advice, anyone?
Can you purchase from New Egg or some of the other computer parts
suppliers on the net?
>> The problem with solder is the temperature compared to the critical
>> temp for the device
> I used to believe the same, but since starting to build SMD equipment by
> reflow soldering in the kitchen oven, and never killing a component, my
> beliefs in this regard have changed! Nowadays I believe that it's pretty
> hard to fry a component by soldering.
At roughly 250C the doping starts to migrate. it normally doesn't cause
an immediate failure, but starts the process of gradual degradation.
>
> Normal 60/40 solder melts at 189 degrees Celsius. Silicon devices can
> operate continuously at 150 degrees junction temperature, and some
> manufacturers claim 175, 200 or even 225 degrees for some devices.
*Most* modern devices should be able to tolerate 200 to 250C for a short
time with out causing a failure. I definitely would not want to operate
one at those temps.
> And
> what they can survive for a few minutes is even higher. I have
> oven-soldered many devices so far, both to circuit boards and to heat
> sinks. I heat the oven to 200 degrees, wait for the solder to melt,
The resolder technique is a good one although it's best done with the
quick heat technique. Most devices will survive the over approach to
resoldering using 60/40. Marginal devices may not so I'd not expect to
see a 100% success but with good quality devices the success ration
should be pretty high. It's conter intuitive but the oven approach
probably end up with a lower temp than using normal solder techniques
with a gun or iron which is much hotter than required to melt the solder.
> wait
> a little more to make sure it really has molten well at every place, and
> then switch off the oven. That has worked great so far.
>
> > and the need to make sure the entire area between
>> the device and heat sink is wetted.
> As long as everything is clean, that's no problem. And even if you get
> some air bubbles trapped in, it's still better than 100% filling with
> thermal grease!
Agreed.
>
>> OTOH there
>> are "solder pastes" available that can be applied to the mating
>> surfaces
> That's what I use. I bought a 10 gram syringe of 63/37 no-clean solder
> paste, and it still lasts. A little of that stuff goes a long way,
> because the layer formed between the part and the PCB or heat sink is
> very thin. When you apply the proper amount, almost none of the solder
> flows out from under the part.
>
> > and then melted by a brief induction pulse
>
> I don't know about that technology. I would be scared to fry sensitive
> parts by inducing such a high current in teh metal as to melt the
> solder!
They also use a high intensity light...I don't remember the name but I'd
been guns using these tubes used to solder copper water pipes in just a
second or two.
> I prefer to use the kitchen oven. That takes about 5 minutes for
> a PCB, and half an hour to solder a large transistor to a thick copper
> plate, but is electrically safe!
>
>> A bucket under the desk would be a disaster for me the fist time I
>> put my feet under the desk.<:-))
> Either bolt down the bucket and put a lid on it, or tie down your feet! ;-)
>
>> What you need are two 1CM square plates, separated by 1 CM which
>> should give a close approximation of the resistivity in ohms per
>> CM^3.
> I just did that test, and got 280 kiloohms. But it seems that the
> resistance from the electrodes into the water is more important than the
> bulk resistivity of the water, because changing the distance between the
> electrodes only produced a small difference in the resistance, while
> inmersing more or less area of them changed the resistance in inverse
> proportion.
I used a piece of solid plexiglass about 1" wide X 1/2" thick and 6
inches long.. ahhh about(25mm W X 12.5mm thick X 152mm long) and
machined a notch in the bottom. The plates wee epoxied in place with the
wired running up through the solid plexiglass. The holes were filled
with resin. The measurements wee consistent regardless of how deep
the probe was inserted.
> In any case it looks like the resistance from side to side of my
> amplifier will be on the order of tens of kiloohms, at least, and that
> should be fine. So I can use spring water!
At these voltages I'd think so.
>> I think the limit we set was on the order of 3000 ohms/CM^3.
> Well, what I got is nearly 100 times better!
>
> > Of
>> course that was with 6 to 8KV, but we used about 12 to 15 feet of
>> hose for isolation.
> I will only have 140V. In principle I would have only about 20cm of hose
> between the sides, but if necessary I can use a longer hose and coil it
> up, to increase the resistance.
>
>> IF you only have water running through, or in the device when it is
>> in operation (IOW it drains back into the bucket when not running)
>> eating metal ions will take a very long time to become a problem as
>> in many years..
> That's a good info!
>
>> Here's a thought...put the coolant exhaust 6" to a foot above the
>> device or higher (what ever is handy) with a quart container (or what
>> ever is handy) in the line. Take the return from the top of the
>> container. When power fails to the pump, you will have a quart (or
>> what ever size container you use) for a safety reserve that will
>> drain back through the device, giving plenty of time to shut down
>> before lack of cooling becomes a problem.
> I have a much better plan: I intend to build a flow sensor into the
> system. No flow, no power to the amp. Digikey has a flow sensor for 18
> dollars that seems to fill the bill for the flow level I expect to use.
> The output is simply a reed switch. I don't like the very wide
> hysteresis that sensor has,
If you are interested in a go/no go IE flow/no flow then the hysteresis
should not be a problem as long as it kicks out soon enough.
> and maybe I can find (or build) something
> better. But even this simple flow sensor should provide pretty good
> protection. Digikey also has better flow sensors, but at several hundred
> dollars apiece, they are out of all consideration.
>
> I plan to switch off the pump during prolonged RX, but keep the circuit
> primed. That doesn't play well with the safety reservoir system.
>
>> I'd really like to build a SS 160 through 6 meter amp capable of
>> 1.5KW CCS with enough overhead to comfortably run that legal limit.
> What for? I can see the need to run 1.5kW key down for a few minutes,
> such as for RTTY and SSTV. But CCS? Hardly. At least I don't see why a
> ham could ever need 1.5kW CCS! Maybe you can give me some example!
Currently I might run as long as 10 minutes on a data transmission, or 5
minutes on slow scan.
>> Many commercial tube amps advertised as a legal limit amp just don't
>> have the power supply or components for sustained operation at the
>> legal limit in SSB or CW let alone digital.
> Yes. They are aimed at hams who WANT CCS specs, but don't NEED them, and
> will never actually use the amp that way! ;-)
I've seen a number of these marginal amps cooked. Either the band
switch, power supply, or tubes. There are a number of amps running
811As and the hams keep turning up the drive. Carl would be a good one
to comment on how well he sees these amps standing up.
I like to see an amp capable of more power than it will be run. If an
amp is designed to run a maximum of 1500 watts which is the legal limit
here, then it is always running at its limits, be they the tube, band
switch, power transformer, or over all power supply. many of these amps
are designed for short duty cycle SSB at the legal limit. Run them on
digital and they don't hold up. Some (the 811's) are designed to run a
1000 or 1200 watts out, but this still is way beyond the ratings of the
tubes. The tubes will put out that much power but at a greatly reduced
life an IM products. Yes, I like the idea of being able to run the
legal limit class A meaning at 1500 hout at say 30% efficiency
I need to run between 5000 and 6000 watts input. at 5000 in - 1500 out
that is 3500 watts of plate dissipation figuring 30% efficiency. At 20%
that's 4500 watts dissipation although in SSB at a 20% duty cycle it is
considerably less. At 5KW PEP in that is only 1000W of dissipation.
Class A may only be 25% efficient which would be 6KW in, but at a 20%
duty cycle that is only 1200 W dissipation, but the tube needs the
emission capability to run 6 KW. So in essence I have an amp that is
capable of roughly 3600W PEP out to only run 1500 out, or will have once
it's finished.
I'll more than likely limit its use to the cooler months as my shop air
conditioner couldn't handle the extra load in the summer.
>> Some of them even push
>> the tubes way beyond their ratings to get the power they do and
>> that's at a greatly reduced tube life.
> That's usual practice in ICAS, and has a long tradition.
True but many tubes like the 811A just aren't up to it and end up with
short life. In the past I've run 1200 watts out of half a dozen sweep
tubes, but they are getting quite pricey if you can find them. When
sweep tubes were a couple dollars each at most and you could get a 1000
to 1200 out we didn't worry a whole lot about tube life, but with the
price of tubes now days hams complain about short life even if they
were running an 811 at twice its ratings. <:-))
>
>> IOW I'd want an amp capable
>> of at least 2KW continuous and preferably 2.5KW that should loaf
>> along at 1500 watts without breaking into a sweat.
> Not a good idea! A 2.5kW amp running at 1.5kW will necessarily be less
> efficient,
Not at all. The FU728F will run just as efficient at 1500 out as it will
running full tilt 2500 out. it just needs to be tuned up for that load
impedance.
> as it will be operating at part load. If you really want to
> broadcast in RTTY around the clock at 1.5kW, then you should build a
> 1.5kW amp with generous thermal capability, and not a 2.5kW amp! IOW,
> the electrical design should be optimized for 1.5kW, but using
> components, cooling, etc, designed to run significantly below the
> temperature limit of each part, at that power.
>
>> The current project is a 4CX3000A7 that I want to run class A.
> Don't allow promoters of energy efficiency to hear that. In this world
> where energy is getting ever more expensive, and energy wasting devices
> draw the scorn of many people, we should be looking at class D, class E,
> and class F, with envelope elimination and restoration. Not really at
> class C, much less class AB, let alone class A!
Class A gives by far the cleanest signal and that is what I'm aiming for.
The others give very poor Im products when used with tubes.
>
> > The
>> problem with the higher power tubes is their size. Plus they use more
>> filament power than the average ham station uses in total power.
> That filament power, even for a class AB amp, is one of the reasons why
> I want to replace my tube amp. I run my house on my own microhydro
> turbine, and in winter I have all the power I want, but in summer it can
> get really scarce. I use battery backup in summer, and drawing 2kW
That's not available here in the Northern flat lands. Wind power is
extremely limited due to the trees and we are far enough North the
efficiency and pay back for solar power isn't even listed on the
charts. I looked into Geo Thermal and our small house is so efficient
they were looking at a payback over between 45 and 50 years over our
present set up. Now I have a farm about 30 miles SW of here that is
part of a large wind farm collective with over 100 turbines and I
believe over 215 or 250 megawatt continuous capability. They only have
2 turbines per square mile so the wind farm is very large and they
figure they will have that listed capacity over 90% of the time.
> pulsed for high power SSB transmission is OK, for short transmissions,
> but running filaments and bleeder resistors and a blower even while in
> RX is unacceptable.
>
>> (Bout ~375 watts) One amp on HF and one for 6-meters. It' d be nice
>> to have one for 2-mters as well. I have the tubes and sockets but
>> not enough components to build complete amps.
> I got two 4CX1500B tubes some time ago, for free. Broadcast pulls. The
> guy said they were still in perfect shape, but I have no means to test
> their emission. Maybe some day I make a cavity amp for two meters
> moonbounce with one of them. But more likely not...
> I have no sockets for them, and would probably have to make them. But
> really a MOSFET amp for HF is a more attractive project to me!
Although still pricey you can use Chinese FU728F sockets. You do have to
turn down the center locating pin by about 0.003" to get it to fit or
carefully ream the hole in the 4CX1500B
I'll be glad to trade you a couple 1 oz tubes of Artic Silver for those
two 4CX1500Bs as they are my standby tubes for the FU728Fs. <:-))
I had a solid state amp on HF and it was a great amp, but the equipment
here stays hooked up 24 X 7 and it's rare to unhook it even during our
many thunderstorms. It just wasn't worth the risk considering my main
tower has been hit at least 17 times. (with no damage)
Here's a shot of the top of the main tower
http://www.rogerhalstead.com/ham_files/Tower29.htm
73
Roger (K8RI)
Manfred. ======================== Visit my hobby homepage!
http://ludens.cl ========================
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