Re: [Amps] New Guy, Old 813 amp

["Tom W8JI" <w8ji@w8ji.com>]

> in swr mode and watch the amp input as I operate...Very 
> stable. BTW,I knew
> abt the filament hum problem Tom mentions....You can`t use 
> ct on the fil
> trans for neg return with a tube that has one side of fil 
> and cathode
> common..Found that out (& cured it)several years ago while 
> playing with a

You also very often cannot pass the dc through the filament 
choke winding that carries filament current.
It can cause hum even without a center tap connection simply 
because of the I*R drop of the copper.

In my amps with the cathode tied to one side of the filament 
I use an entirely different choke for the cathode path. Not 
the bifilar choke the filament uses.

73 Tom



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