[Amps] Liquid cooling

Wed Aug 24 14:21:18 PDT 2011

Find out where the gamers and overclockers get their compounds; Chile is no 
exception.

Carl
KM1H

----- Original Message ----- 
From: <TexasRF at aol.com>
To: <manfred at ludens.cl>; <amps at contesting.com>
Sent: Wednesday, August 24, 2011 3:24 PM
Subject: Re: [Amps] Liquid cooling

> Manfred, are there computer repair shops there? Many of the thermal grease
> products are targeted for CPU cooling applications.
>
> 73,
> Gerald K5GW
>
>
>
>
> In a message dated 8/24/2011 2:19:19 P.M. Central Daylight Time,
> manfred at ludens.cl writes:
>
> 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
> easily get the usual white ceramic thermal compound, packaged in  little
> jars with no label, so I don't know what's really inside! 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?
>
>> 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.
>
> 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.  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, 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!
>
>> 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! 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.
>
> 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!
>
>> 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, 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!
>
>> 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! ;-)
>
>> 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.
>
>> 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, 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!
>
>>  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
> 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!
>
> Manfred.
>
> ========================
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> http://ludens.cl
> ========================
>
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