[Amps] 12V IM3

[Roger (K8RI)]

I know, which is one of the reasons I used it.  The CPI (inflation) is a 
fictitious number just like unemployment.

Electronics except for specialty items has benefited from scale. That 
Collins station was nearly a half the average years wages and it only 
did two things, but it did them very well with an exceptionally clean 
signal.  My first computer if scaled to today's memory size and CPU 
speed would cost over 20 million dollars without resorting to the CPI 
and my house isn't large enough to house all the chips. Imagine 
recreating today's "super rigs" using tubes. The power it would take and 
the heat it would develop!

As several have pointed out, we try to get the most out of our rigs. As 
far as I recollect, it's almost alwys been that way, but the 
shortcomings of tubes being pushed is little compared to solid state 
being pushed. As Jim pointed out, there are commercial rigs with good IM 
because the run the finals (and other stages) conservatively.  I still 
believe the IM3 is important for adjacent signals.

When 2 devices are capable of 1500 watts (barely) we can run 4 that 
would be good for 3,000 watts at 1500 out for a much cleaner signal.  
There are additional complications, but the basic premise is valid. Yes 
they cost more, but the protective circuitry becomes much lless 
critical.  You can use more negative feedback while still getting the 
legal limit out. A much cleaner output as you are moving well away from 
compression.

The argument comes up that they are less efficient when run that way, 
but are they if the circuit is designed for 1500 out using devices 
capable of twice that?  But what if they are less efficient?  So what?  
I can get rid of heat a lot easier than fixing a crappy signal.  The 
biggest heat problem is "spreading" the heat from a small spot to one 
large enough that it can dissipate the heat into air with out losing 
your hearing.

Computers solved this problem nicely.  Remember those little 90 mm high 
speed, screaming fans of the early days? We now use a pair of side by 
side 140 mm fans coasting along as they blow air through a radiator.  
There are several things as hams we can learn from this even if those 
devices, in their current form are incapable of handling the heat load 
we are dumping.
One is using a medium to transfer the heat somewhere else where we can 
get rid of it. instead of a copper heat spreader connected directly to a 
fan cooled heatsink.  High powered CPUs which operate at temps only a 
bit less than power transistors use heat pipes to carry heat to the fan 
cooled heatsinks, or even water in a closed loop circuit..

We can also learn from industry and use chilled water in a closed loop.  
Like remoting a noisy 4CX3000 amp, all the noise making stuff is 
somewhere else. You embed copper tubing carrying chilled water directly 
in that copper plate heat spreader with or without a fan cooled heatsink 
for a safety in case the water flow stops. Of course, you can use plain 
old tap water because we don't care if it's conductive and automatically 
switch if the chilled water fails

The point with more devices is multifold.  Holding a temperature becomes 
less critical, protection circuits for drive and outout power become 
more tollerant. IOW that protective circuitry can become a bit more 
simple. HOWEVER  you do have to be careful about condensation.


73

Roger (K8RI)


On 5/22/2015 1:57 PM, Michael Clarson wrote:
> Roger: While many of the technical points are valid, using Consumer Price
> Index  (CPI) to compare "rig" prices is not realistic. Electronics,
> particularly consumer electronics is the outlier -- it does NOT follow the
> CPI..For example, a typical TV now is a 42", which goes for $450 in 2015. A
> 21" RCA color tabletop TV would cost $500 in 1960. Using the CPI, that
> would be almost $4000 in today's dollars, BUT, a $450 42" TV (Typical,
> today) would cost $56 in 1960 dollars. Its just not fair to use CPI to
> compare then and now electronics prices. Too much has changed. I used TVs.
> It becomes even more absurd when comparing digital computers!. --Mike,
> WV2ZOW
>
> On Fri, May 22, 2015 at 1:28 PM, Ken K6MR <k6mr at outlook.com> wrote:
>
<whole bunch of snip>

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