[AMPS] follow-up: filament voltage questions

[Rich Measures]

>
>As a follow-up to my earlier post:
>
>I measure the L7 filament voltage at 5.14 VAC using the aforementioned
>Fluke 77 DVM.
>
>An oscilloscope across this same test point shows no power-on 'bang' - so
>the transformer is performing well in this manner, no inrush surge to worry
>about.
>
>So guys, should I bother with fiddling about 0.14 volt?  This is 2.7% high,
>per my calculator...
>
>
Steve:  3% high cuts the emissive life in half.  6% high cuts the 
emissive life by 3/4.  {see amplifier article in Jan. 1994 QST for 
details}  //  To measure the inrush current you need to measure the peak 
voltage drop across a known series resistance with the oscilloscope.  The 
fil choke can serve as the known series res.  To measure the resistance 
of the choke,  pass 1.00 ampere DC through the fil. choke and measure the 
potential dropped across the choke with a DMM.  A typ. value might be 
5.0mV - which means that the choke has 5.0 milliohms.  //  Connect the 
oscilloscope across the 5.0 milliohms.  Start the amp. and measure the 
peak v.   Current equals volts div. by 0.005 ohms.  
>
-  later


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm