[Henry] Filament Transformers

Thu, 11 Dec 2003 12:15:44 -0800

Hi Gene,

Good questions.

Henry uses a very simple method to control inrush current of the filament
supply. They use a filament transformer properly rated for the filament
current of the tubes(s). So, when they are cold and the filament draws lots
of current during that first fraction of a second warm up, the voltage drop
is quite large and there transformer just "sags". The inrush current is
controlled by the transformers inability to supply more current than it is
rated for. This is where you definitely don't want a largely overrated
(current wise) filament transformer.
To measure filament voltage make sure HV is disconnected (for safety
reasons) and measure at the tube socket. I have put a 50 watt 25 ohm
variable resistor in series with the PRIMARY of the filament transformer and
adjust voltage down until power output starts to drop off, then back up
another .1 volt or so.  

73, Dan Magro W7RF
HENRY RF Power Amplifiers
BIRD power measuring, TOHTSU coaxial relays
SAMLEX power supply, RFI snap-on chokes
www.radiodan.com <http://www.radiodan.com>  [email protected]
<mailto:[email protected]>  

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Gene Bigham
Sent: Thursday, December 11, 2003 5:33 AM
To: [email protected]
Subject: [Henry] Filament Transformers

I have a Henry 2K Classic X, with the separate filament transformer and
heavy duty innards.  Question with all this concern about 3-500ZG tube
filament voltage and inrush current; how does the Henry limit inrush current
or does it?  And how is the voltage to the filaments controlled and with the
case being like it is how do you measure at the tube base this voltage
safely to see if it needs adjusted?
Thanks
Gene Bigham
KB0GU

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