Date: Sun, 10 Apr 2011 04:49:23 -0400
From: "Roger (sub1)" <sub1@rogerhalstead.com>
Subject: Re: [Amps] Alpha vs Henry
The imaging systems will show the temp variations in the rising air.
OTOH as John says, the question is immaterial because (paraphrased) the
tube will be hotter than the air leaving it.
### whoa. Exhaust air temp from a metal tube VS anode temp is apples and
oranges.
The more efficient the anode cooler is, the more heat it will extract, and the
exhaust air temp
will be HOTTER. A fluke IR gun, like a mini 62 will tell you the temp of
the upper fins..and that's
about it. The SEAL temp is what you have to worry about...where the lower fins
meet the ceramic stem !
And you can't point an IR gun at the seal, since in normal operation, the
chimney is covering it up! The
real test is those temp sensitive crayons that John mentioned, and also in the
Eimac literature.
## Eimac sez a 3CX-3000A7 requires 67 cfm @ 1.2" ... IF the intake air temp is
40 deg C [104 deg F]. Now, I'm
not about to fire up any amp, when it's 104 deg F in the shack. That being
the case, if the room temp is
a more normal say 20-25 deg C ....[it's 15 deg C in my basement shop where the
amp is] you can then
get away with LESS cfm and LESS pressure on any blower...and still get the job
done. That 67 cfm is for
4 kw CCS anode diss + 225 w CCS grid diss...and 375 w CCS for the cathode.
[ 4.6 kw CCS total]
Now the fil is on all the time, but with cw/ssb, the average anode and grid
diss is very low, even with 2-5
kw pep out. OK, now we can reduce the airflow even more.
## The 3CX6000A7, per Eimac, wants to see 204 cfm @ .4".....again IF the
intake air temp is 40 deg C. That
assumes 6 kw CCs anode diss, 225 w CCs grid diss... and 560 w CCS fil diss ...[
6785 w CCS total]
### 6785/4600 = 1.475 more total diss for the bigger tube. 1.475 x 67
cfm = 99cfm.
Now the 3CX-6000A7 wants to see 204 cfm..and not 99 cfm. When I ram 204 cfm
through a 3CX-6000A7,
the exhaust air temp is cooler than the exhaust air temp from a 3CX-3000A7.
The anode cooler on the
3X6 tube is not as efficient at extracting heat, and the result is a lower
exhaust air temp ! The bigger
tube is dissipating 47.5% more power.... but requires 300% more cfm /
airflow.......[and not 47.5 %]
## Bottom line is.... be real careful about trying to correlate exhaust air
temp VS anode temp. Those temp sensitive
crayons are the real deal..and the only reliable way to obtain meaningful data.
One other point, I've seen the question raised about how much pressure
was a fan generating. For a given tube and existing system you can
treat air flow and pressure the same as voltage and current. IF you are
getting the required air flow you MUST have the required air pressure.
Insufficient pressure and you will have insufficient flow. Get the
proper flow and you will have the proper pressure.
IF the radiator is plugged or partially clogged you will have high
pressure and low flow. But again, it the flow if proper then so is the
pressure.
### Not quite. When Eimac specifies a pressure, like in the above case, they
assume a few things,
like the correct mating Eimac socket is being used, and also the mating chimney
and anode connector. Eimac
also assumes a relatively Un-cluttered area below the chassis, around the
socket. They also assume the manometer
is NOT being installed is such a fashion that the airflow is screwed
up....affecting results. Eimac also assumes that folks
are positioning the outlet of the blower correctly. Now if joe ham wants
to install the blower on the rear panel..and the
blower is pointed directly across the base of the tube socket, it will create a
venturi effect, and screw up the airflow.
You will get a similar result if say the blower is mounted on top of the
chassis..and pointing down though a hole. The air in
that case goes straight down a few inch's, hits the bottom chassis cover, then
has to do a 90 deg bend asap. It then flows
along the chassis, then has to do yet another 90 deg bend..and go up through
the socket.
## Now contrast that with mounting the blower a 3rd way... bolted to bottom of
chassis cover... with exhaust pointed straight up..
and directly into the socket... and NO 90 bends at all. You also have to
factor in stuff like bifilar rods, tuned inputs, relays, and what ever
other junk is below the chassis, that can slow down air flow. [ lets call it
resistance]
## Roger's analogy is correct..except he left out the resistance..and assumed
it was zero. voltage = pressure current = cfm
and resistance = cluttered below chassis area and/ or too many 90 deg bends
in the airflow.
## Toss in some resistance, then add even more.... and you will see that
you need more PRESSURE to get the same cfm.
I use these Dwyer magnehelic gauges, and they are very sensitive. The hb
water in a bent tube type work good too.
But you will get an eye opener when you move the manometer/magnehelic about
the chassis. Eimac does not specify or
make, nor sell, a socket or chimney for either a 3x3 or a 3x6 tube. Henry
radio really restricted the airflow on their 3x3 tube,
in their 8-K ultra. Other's have restricted the airflow to the base of the
3x6 tube. The holes/slots/etc you put into the chassis,
should at least be equal.......or greater, VS the under-fin area of the tube.
For folks who opt to use straight up and down chimney's
on 3x3, 3x6 and YC-156's... you will be severely bottle necking the airflow,
resulting in a huge increase in pressure requirements.
later........ Jim VE7RF
73
Roger (K8RI)
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