[AMPS] Filament circuit design

[Rich Measures]

>
>Hello all
>
>I'm constructing a tetrode amp. and the filament transformer
>I have has no centre-tap.    I do not want to 'earth' one side
>of the filament.,
>
>Any suggestions as to how I can monitor the cathode current ?
>(The HV- would normally be connected to the centre-tap of the
>filament xfmr. and the cathode current metering between this
>point and 'earth')   One idea I had was to make an 'artificial'
>centre-tap by connecting a low-value wirewound resistor to 
>each side of the filament, and take the HV- to where they join.
>(checking that not too much filament AC current flows through
>these 2 resistors)   

The 2-res. artificial CT works ok.  Typically, 5-10% of the rated 
filament current flows through the artificial CT.   Another method is to 
wind a 7.5vac or so 60Hz CT autotransformer.  The wire size can be quite 
small since the current in each wire is half the cathode current.   
-  later, Chris.


Rich...

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


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