[Boatanchors] Long-term AC voltage monitor

[Jim Wilhite]

Let me see if I understand the logic here.  I am supposed to measure the 
filament voltage of the tubes in my equipment and if it exceeds 6.3 volts I 
must take steps to alter it to that level?  Am I right?   By doing that, I 
will extend the life of the tube.  Guys, I probably won't live that long.

I just replaced three rectifier tubes in my GK 500A last week that I have 
owned since 1994, so after this discussion I went to look at the date codes 
on the bad ones.  Two were so old that they didn't have date codes and one 
was a 67 code, all supplied with the equipment when sold.  I also know the 
transmitter specification is for 115 volts +/- 10% 50/60 cycles which should 
mean the filament voltages are over 6.3 volts.  My line voltage, the last 
time it was measured about a year back was 125 volts.  The lineman used an 
analog voltmeter that is about (maybe) 10% accurate but who knows since it 
has bounced around in his truck for the past N of years.

Now whose voltmeter should I used to be certain that the voltage is above 
115 or whatever?  You may use a meter traceable to NIST standards, but will 
your electric company lineman?  And since all meters are manufactured to 
certain specifications, what is yours?  Have you sent it to a metrology lab 
to be calibrated?  Does it meet specs as published with the manual 
accompanying the equipment?  I have three meters, A fluke 77, a fluke (some 
other number) and a Cen-tec and all give different readings.  Which should I 
use?  All are manufactured to NIST standards.

Ok I stated earlier that the line voltage is +/- 10%.    Given the tubes we 
use were manufactured before 1970, what tolerance do you think the 
manufacturer used to make the filament for them?  I would bet on +/- 10%. 
You do the math on the filament voltage.

The point in all this is that we can obsess about these things like the 
wife's tale about rotating your power tubes to keep gas out of them.

Jim
W5JO