[Amps] Heat Measurement in Amps

[Jim Thomson]

Date: Thu, 10 Jun 2010 11:07:37 -0700
From: Patrick Barthelow <apolloeme at 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 from 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