Date: Thu, 10 Jun 2010 11:07:37 -0700
From: Patrick Barthelow <apolloeme@live.com>
Subject: [Amps] Heat Measurement in Amps
Has anyone found a decent cheap temperature sensor/guage (perhaps even at
harbor freight, etc) that you could place at a specified location in the
exhaust airstream of the tubes, of various amps to see and record what is
"normal" temp ranges? Maybe the brain trust here, could search out a standard,
cheap temp measurement sensor (some DVMs have them) and do some testing and
publishing of expected exhaust air temps of various amps in various modes, like
Low duty cycle (SSB), medium (CW) or high (RTTY)
If the sensor was IR optical you could also watch temps on transforer cores,
with use, and get a database going, on what is "normal". Or what Manufacturer
is really pushing the heat limits on their products.
## for safety... I use a fluke mini 62 point and shoot IR.... and got a real
surprise at how hot that tubing coil gets in the L4B [ I have 4 of em]. With
HV interlock defeated... and using the footswitch.. hit it with a 800 ma cxr...
then off... then put ur finger on the tank coil... yikes.... hot. [15m] Even
hotter on 10m. One would that when on 15m.... the UN-used portion of the
tank coil would heat sink the hot portion.... it doesn't. It's hottest
right at the tap on the coil. Move finger one turn over.. and it's just warm.
So much for my theory of the Un used portion heatsinking the hot parts. I
used the fluke 62 to measure heat of xfmr's, windings, taps, bandswitch's,
roller contacts, baluns, all sorts of dangerous stuff..esp with larger metal
tubes. Be careful when trying to correlate exhaust air temps with anode
temps. A tube with a more EFF anode cooler [metal tube] will have a hotter
exhaust air temp. It's extracting more heat fr
om the anode. [ it also may well require more pressure] . If the tube seal
is good for 250 deg C........[ and say at 225 C deg]... the exhaust air temp
will be way less. If it's say....150 deg F.... then use that as ur ref.
If u see it go > 150 deg F ... then u know the anode is > 225 deg C.
A muffin fan on the top (sucking, straight above the chimneys) of a Drake L-4B
in heavy duty contest mode REALLY cools the cabinet, and might do some
effective coolings of the critical innards.
## run the L4B [temp] with no lid on at all... and everything is just fine...
it's all cool [ except the chimney's ] The cab is the problem [top lid]
You can't get air through those small holes.
Same thing with a muffin fan on the perforated cover of the L-4B Power
supply....but I dont know if that really cools the transformer core very much.
### Toss those useless 50 w bleeder resistor's. The pwr supply cab will
run stone cold then. All that heat is coming from the pair of 50 w ww
bleeders. The amp already has 100 k EQ resistor's across each cap as
is. I expected the NO load B+ to soar.. and it doesn't budge... still 2650
vdc. Re wire the cut off bias with a 100 k 3 watt mof in the CT of the fil
xfmr [ yellow wire].. and short it out on TX... using the center contacts of
the 3PDT t/r relay. The original drake scheme used a 7k 5 watt resistor
in series with the pair of bleeders. The 90 vdc across the 7 k resistor was
the cut off bias. [ which is way less than 90 vdc.. when on lower B+.. CW
mode].
## I use 10 x 1N5408's in series for bias.. and put that in series with the
CT as well. Then the idle ZSAC is way down............ no more 230 ma of idle
= 600 watts = blast furnace. Then the whole thing runs cool.
later........ Jim VE7RF
Best Regards,
73, de Pat Barthelow AA6EG
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