Re: [Amps] Measuring filament voltage

[Steve <g8gsq72@gmail.com>]

Good additional and practical points from John. Higher value resistors 
might suit in some situations - don't forget to allow for the error 
introduced by the 'pot down' of the resistors against the DVM input 
resistance. With 2 x 10k and 10Mohms it's 0.2%.
Steve G8GSQ

> Steve's approach is an acceptable method to read the filament on a common grid 
> HF amplifier. The 10 K resistors would optimally be carbon film or comp and not 
> wirewound, so that they are non inductive and have lowest capacitance from end 
> to end. There will be RF voltage across it!  I would probably put a 10 nF cap 
> to ground on each cold lead to the meter as well, keeping all of that close to 
> the resistors in an enclosure in the amplifier. The capacitors should be mica 
> with short leads or quality ceramic. The resistors should be bigger than 1/2 
> watt just for the RF voltage. Not for dissipation. Just remember to test it 
> with and without RF drive applied to see if there is RF affecting the reading 
> or not. An analog rms meter will likely ignore it.
>
>
> 73
>
> John
>
> K5PRO
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