RE: [TCML] 7.5V 52A Filament Transformer for 3CX3000 Needed

["S&JY" <youngs@xxxxxxxxx>]

Cameron,

Regarding in-rush current control, hams have long controlled the inrush
current on their larger transmitter plate power supplies, when first turned
on and charging their filter caps.  Typically, they use a relay activated by
a timer to add a big power resistor in series with the plate transformer
primary.  This allows the filter caps to charge for a few seconds, then the
power resistor is switched out by the relay.

You could provide a similar "soft start" circuit with your filament supply.
For example, let the filaments warm up at half-voltage for a minute or two,
then the timer-relay would activate to apply the full filament voltage.  The
relay-timer circuit ought to be in the primary of your filament transformer
where the current being switched is much lower than in your filament
circuit.  I believe such an arrangement would contribute to significantly
longer tube life, as well as eliminating the need for a variac.

Steve Y.

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Quarkster
Sent: Sunday, June 14, 2009 1:20 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] 7.5V 52A Filament Transformer for 3CX3000 Needed

Cameron -

Another option (regardless of what transformer you use) is to use a variac 
on the primary side of a filament transformer. This allows you to have 
superior control over inrush current as well as being able to precisely 
adjust filament voltage at the tube socket.

I appreciate your desire to use a commercially-made, appropriately-rated 
transformer as it just makes a "professional" appearing setup, better than 
any "home-brewed" transformer could.

Regards,
Herr Zapp


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